HUME, DAVID
(1711–1776)

David Hume, considered by many the finest Anglophone philosopher, one of the first fully modern secular minds, and, along with Adam Smith, the leading light of the Scottish Enlightenment, was the author of four major philosophical works and many essays.

Born on April 26, 1711, in Edinburgh, Scotland, Hume spent his childhood mostly at Ninewells, the family estate near Berwick. Though his family was of good social standing, they were not rich, and, as the second son, he had to be prepared to earn a living to supplement an inadequate inherited income. He attended Edinburgh University from the ages of eleven to fifteen, in which city he remained to study law. Finding this not to his taste, Hume returned to Ninewells and threw himself into an intensive program of intellectual self-development. He read widely in ancient and modern literature, improved his knowledge of science and languages, and devoted himself above all to philosophy. In this way, sometime before he turned eighteen, Hume achieved the breakthrough that, he reported, "open'd up to me a new Scene of thought, which transported me beyond Measure, & made me, with an Ardor natural to young men, throw up every other Pleasure or Business to apply entirely to it" (The Letters of David Hume 1932, vol. 1, pp. 13–14).

However, the strain eventually told on Hume's health, and he was obliged to curtail his studies and pursue a more active life. To this end, he secured employment with a Bristol merchant in 1734. Though this venture into the world of commerce was brief, his health was sufficiently restored to enable him to undertake the composition of the systematic philosophical treatise by which he hoped to make his literary mark. To stretch his meager income further than was possible in Britain, Hume relocated to France—first to Reims, then to La Flèche in Anjou—where he was able to benefit from the outstanding library of the Jesuit college.

Hume returned to England in 1737 with the intention of publishing the first two books, Of the Understanding and Of the Passions, of the work he decided to call A Treatise of Human Nature: Being an Attempt to Introduce the Experimental Method of Reasoning into Moral Subjects. After publishing them as volume 1 in 1739, he went home to Scotland to revise the third book, Of Morals, which he published as volume 2 the following year. Never before or since has anyone so young published a philosophical work so comprehensive, ambitious, original, or accomplished. Still, Hume's obvious aspiration to be acknowledged the Isaac Newton of philosophy did not sit well with contemporaries. Reviewers were mostly hostile and uncomprehending, so that the Treatise "fell dead-born from the Press ; without reaching such distinction as even to excite a Murmur among the Zealots" (1987, p. xxxiv).

Having wisely taken the precaution to publish anonymously, Hume soon recovered from his failure and decided to apply his immense literary gifts to the more widely accessible medium of the essay. His Essays, Moral and Political of 1741 and 1742 duly succeeded where the Treatise failed. With a public won, together with a keen sense of its tastes, Hume presented a selection of the doctrines of the Treatise with some previously unpublished material in the form of Philosophical Essays concerning Human Understanding in 1748 (retitled An Enquiry concerning Human Understanding in 1758). With its companion published three years later, An Enquiry concerning the Principles of Morals, Hume firmly established his reputation as one of the leading philosophical thinkers of his day. Around the same time Hume composed his Dialogues concerning Natural Religion, but was prevailed on not to publish it during his lifetime. From that point on, Hume devoted himself to essays and wrote his most popularly successful work of all: the six-volume History of England: From the Invasion of Julius Caesar to the Revolution of 1688 (1754–1762).

Hume held a number of posts during his life, though he never succeeded in securing an academic position. In 1745 he served as tutor to the mentally unbalanced Marquess of Annandale. From 1746 to 1749 he was secretary to Lieutenant-General James St. Clair (1720–1806), whom he accompanied on a military expedition to Brittany. He was keeper of the Advocates Library in Edinburgh from 1752 to 1757. In 1763 Hume became private secretary to Lord Hertford (1718–1794), the British ambassador to France, where he spent the next three years being continually fêted and forming friendships with several leading figures of the French Enlightenment, including Denis Diderot, Jean Le Rond d'Alembert, and Jean-Jacques Rousseau (though this last connection was to end in conflict). The last position he held was that of secretary of state in the Northern Department, from 1767 to 1768.

Physically, Hume was tall, somewhat ungainly, and, by the mid-1740s, corpulent. He never married, initially for lack of means to support a family, and afterward from a preference for bachelor life. Hume's most extraordinary quality was his personality. Warm, generous, eventempered, and honorable in all matters, he gained and kept an enormous number of close, devoted friends. This included many prominent clergymen who time and again staunchly defended him against his persecutors. Hume was thus able to spend his final years in Scotland in tranquillity, surrounded by well-wishing friends and family. When death came on August 25, 1776, he took it in the best spirit imaginable, while also making sure that no tales could be spread that his religious skepticism had weakened in the end.

Hume's influence on philosophy during his lifetime was nothing like what it later became. His moral theory undoubtedly made an impact on Smith's Theory of Moral Sentiments (1759), while his theory of the understanding provided Thomas Reid with his principal foil in Inquiry into the Human Mind, on the Principles of Common Sense (1764). Reid and other less respectful philosophers of the Scottish "commonsense" school focused many of their severest criticisms on the Treatise. Their misunderstandings and misrepresentations of that work so infuriated Hume that he published an advertisement with the final edition of the Enquiries produced under his supervision (1777), desiring that these maturer efforts would "alone be regarded as containing his philosophical sentiments and principles."

A sea change in the reception of Hume's theory of understanding occurred in 1783, when Immanuel Kant declared that Hume's treatment of cause and effect was responsible for awakening him from his dogmatic slumber. Kant's own transcendent importance in the history of philosophy, and the scholarly attention devoted to almost his every word, led to a reappraisal of the worth and importance of the philosopher Kant credited with making his achievements possible, and it was not long till the Treatise came to be recognized as Hume's masterpiece.

Being cast as Kant's John the Baptist did, however, have its downside, and many have labored to bring Hume's legacy out from under the shadow of Kant. Influenced by the latter, philosophers in the nineteenth century, and for much of the twentieth as well, tended to esteem Hume almost exclusively for the power of his skeptical arguments regarding reason, the natural world, and religion. Since then, the positive, constructivist aspects of his theory of understanding have come to be equally prized, as have his theories of passion, actions, morality, and aesthetics. Today, interest in Hume's philosophy is greater than ever and the wave shows no sign of cresting.

The Treatise and the Enquiries

Most scholars accept the essential correctness of Hume's assertion that there are few substantive differences between the Treatise and the Enquiries, and none of great consequence. Instead, the earlier and later works differ primarily in inclusiveness and style. The Treatise was pitched at the highest level, to pass muster with the most learned, exigent readers. Questions left unraised in the Enquiries were pursued at considerable length, whole batteries of arguments were assembled in support of major theses, and every effort was made to be both systematic and comprehensive.

By contrast, the Enquiries were aimed at the same readers who enjoyed Hume's more philosophical essays. This seems to have been the principal reason for his decision to omit from the first Enquiry almost everything in parts 2, "Of the Ideas of Space and Time," and 4, "Of the Skeptical and Other Systems of Philosophy," of book 1 of the Treatise. Much of parts 1, "Of Ideas," and 3, "Of Knowledge and Probability," were also sacrificed, so that what remains seems less like a condensation of the Treatise than a greatly expanded and improved version of the abstract of the Treatise that Hume published in 1740. The second Enquiry drew on the moral philosophy of book 3 of the Treatise, while eschewing the theoretical framework of the latter in favor of a more strictly literary approach (which both explains why Hume thought it his finest work and why so few today agree). Neither Enquiry contains any considerable trace of book 2 of the Treatise, on the passions, and though occasional echoes of it are to be found in Hume's essays, they give no idea of the impressive, highly sophisticated theoretical framework one finds in book 2 of the Treatise (and the same is true of Hume's A Dissertation on the Passions [1757]). Thus, despite Hume's wish not to be judged by the Treatise, its unity, scope, and rigor make it the work that best represents what is most important and enduring in his philosophy.

Hume's Science of Human Nature

Hume believed human nature to be the proper focus of the philosopher because its first principles necessarily carry over to every human endeavor, cognitive and conative alike. A science of human nature affords fundamental insight not only into such domains as morals, aesthetics, and politics but "even Mathematics, Natural Philosophy, and Natural Religion," which "are in some measure dependent on the science of MAN; since they lie under the cognizance of men, and are judged of by their powers and faculties" (1978, p. xv). Situating himself in the line of British empiricist thinkers extending from Francis Bacon and John Locke, Hume restricted the investigation of human nature to evidence gleaned from "careful and exact experiments, and the observation of those particular effects, which result from its different circumstances and situations" (p. xvii). It constitutes a science insofar as one "must endeavour to render all our principles as universal as possible, by tracing up our experiments to the utmost, and explaining all effects from the simplest and fewest causes." This may require one to revise initial determinations in the light of new experiments (Hume's evolving characterization of the difference between memory and imagination is a prime example), and obliges one to determine whether the fundamental principles of human nature have even wider scope (thus, Hume considered it a plus that much of his account of human nature extends to animals as well). Finally, the mandate for maximal simplicity means that the science of man should take the form of a system, deriving its principal authority from "the agreement of [its] parts, and the necessity of one to explain another" (p. 154).

The Elements of Hume's Science of Human Nature

objects

Hume considered human nature always and only in terms of perceptions. Perception is Hume's substitute for Locke's term idea, and it refers to all objects insofar as they are immediately present to one by consciousness, be it in sensation, reflexion, or thought (reflexion is Hume's catch-all term for the objects present to internal sense or inward sentiment, including passions, emotions, desires, volitions, and mental operations generally). For Hume, just as for Locke with idea, the indeterminacy of perception —the impossibility of contrasting it with anything that is not a perception because "[t]he mind never has anything present to it but the perceptions"—is its principal virtue. If things other than perceptions exist, then, as what never "can be present to the mind, whether we employ our senses, or are actuated with passion, or exercise our thought and reflection" (1999, p. 202), they are no different from perfect nonentities so far as one's thoughts and actions are concerned. By contrast, even objects as fanciful as a billiard ball that transforms itself into wedding cake on being struck, though never present to the senses, are still objects of one's thought, and so too perceptions.

Perceptions come in two kinds: impressions and ideas. Impressions comprise sensations and reflexions, and ideas thoughts (the mental contents of thought, considered in themselves rather than in the capacity of signs used to signify other perceptions, whether by resemblance, linguistically, or in any other significative capacity). According to Hume, the difference between impressions and ideas consists in the greater "force and vivacity" of the former. This does not mean that impressions always make a forceful impression, for they can be so gentle as altogether to escape notice. Nor does it mean that they are vivid in the usual sense, since seeing a gray blur on an otherwise black night (visual sensation) is still more vivid than a brilliantly lit, detailed image in a daydream (visual idea).

The best indication of what Hume had in mind by "force and vivacity" is his subsequent equation of it with belief in the real existence of a content present to one in sensation, reflexion, or thought, all perceptions. According to Hume one believes in the reality of something that one merely thinks if one's conception of it exhibits force and vivacity, as when, on seeing smoke coming into the room, one not only thinks of a fire somewhere outside the room but believes that a fire really exists. Similarly, "the belief or assent, which always attends the … senses, is nothing but the vivacity of those perceptions they present" (1978, p. 86). More particularly, the vivacity of a perception seems to consist in a feeling distinctive of the manner in which an object in sensation or reflexion is apprehended, or an object in thought is conceived, in virtue of which it is regarded as really existent—actual rather than merely possible, fact rather than fiction.

If this reading is correct, then one needs to distinguish two senses of exists in Hume: an object, even if it is a mere fiction, exists simply in being present to consciousness (p. 66–67), but it is taken to be really existent if, in addition, it is perceived or conceived in a lively manner (pp. 84–123). Sensations and reflexions are impressions because human (and animal) nature is so constituted that these objects have only to appear to be believed really existent, whereas objects present to one only in thought are not believed really to exist unless circumstances intervene to induce one to conceive them with a high enough degree of force and vivacity. One of the principal occupations of Hume's theory of understanding was to determine what those circumstances are and to identify the underlying principles.

Finally, Hume distinguished perceptions according to whether they are complex or simple. In general, an impression or idea counts as simple if it cannot be distinguished into two or more components (different significative uses to which the same simple perception may be put do not compromise its intrinsic simplicity). But Hume also seems to allow that perceptions distinguishable in this way may still be simple if it is impossible for them to be derived by the combination or blending of perceptions already in one's possession (e.g., "The impressions of touch are simple impressions, except when consider'd with regard to their extension" [1978, pp. 230–231]).

the copy principle and hume's theory of origins

The "full examination" of the question of how impressions and ideas "stand with regard to their existence, and which of the impressions and ideas are causes and which effects" is "the subject of the present treatise" (1978, p. 4). To this end, Hume notes that one's simplest perceptions all seem to come in duplicate impressions and nearly exactly resembling ideas, and asks if there is any causal significance to this relation. He then formulates perhaps the most important principle of his science of human nature: because experience shows that simple impressions invariably precede their resembling ideas, "all our simple ideas in their first appearance are deriv'd from simple impressions, which are correspondent to them, and which they exactly represent" (p. 4). The causal dependence of ideas on impressions expressed in Hume's copy principle owes its importance to his preeminent methodological concern to find a better method of clarifying the ideas at the heart of traditional metaphysical disputes than definition can provide:

Complex ideas may, perhaps, be well known by definition, which is nothing but an enumeration of those parts or simple ideas, that compose them. But when we have pushed up definitions to the most simple ideas, and find still some ambiguity and obscurity; what resource are we then possessed of? By what invention can we throw light upon these ideas, and render them altogether precise and determinate to our intellectual view? Produce the impressions or original sentiments, from which the ideas are copied. These impressions are all strong and sensible. They admit not of ambiguity. They are not only placed in a full light themselves, but may throw light on their correspondent ideas, which lie in obscurity. And by this means, we may perhaps attain a new microscope or species of optics, by which, in the moral sciences, the most minute, and most simple ideas may be so enlarged as to fall readily under our apprehension, and be equally known with the grossest and most sensible ideas, that can be the object of our enquiry.
(1999, pp. 135–136)

Hume's science of human nature is, in the first instance, a critique of traditional philosophical definitions whereby they are supplemented or, more usually, supplanted, by psychological accounts tracing ideas to their originating impressions. These accounts inform everything else in the science, and it is often impossible to understand the positions Hume takes without returning to his explications of the relevant ideas in terms of their originating impressions.

relations

To understand the nature of relation for Hume, one first needs to consider the two ways in which relations may be affirmed. If one can affirm a relation independently of the senses, and so of all matters of fact and real existence, one's affirmation is a case of knowledge and the relation affirmed is a necessary one. For "the necessity, which makes two times two equal to four, or three angles of a triangle equal to two right ones, lies only in the act of the understanding, by which we consider and compare these ideas" (1978, p. 166). When immediate, the knowledge of a relation is intuition, when it consists of a continuous sequence of intuitions, it is a demonstration.

Knowledge of a relation of ideas is attainable (1) when one is sensible of the impossibility of forming one idea without including another as a constituent, as, for example, one cannot form the idea of a valley without incorporating into one's conception the idea of mountains (p. 32), or, (2) even if the ideas can be conceived separately, one is sensible of the impossibility of conceiving a change in their relation without conceiving a change in the ideas themselves (p. 69), as "the shortest distance between two points is sa straight line" is known to be necessary even though shortness (a quantity) and straightness (a quality) are conceivable independently (pp. 49–50). (The first type coincides with Kant's notion of an analytic judgment, the second with that of a synthetic a priori judgment; Hume did not, however, see fit to subdivide intuitive knowledge this way, that is, he either did not recognize or did not attribute to the question of the possibility of synthetic a priori judgments the same importance Kant would afterward accord it.) Either way, one's affirmation of a relation amounts to knowledge if and only if one is sensible of the impossibility of conceiving the ideas concerned in any other relation (pp. 652–653).

Where knowledge is lacking, and other relations between the ideas (or none at all) are conceivable, one can still affirm a relation between distinct perceptions with probability, that is, with a certainty extending anywhere from just above logical possibility all the way to a certainty so great as to be immune to doubt (termed proofs by Hume, e.g. "the sun will rise tomorrow" and "all men must die"). Such relations consist essentially in transitions of thought characterized by a quality Hume termed facility (1978, pp. 99, 204, 220, 260). There is considerable evidence that Hume conceived of facility as affective; that is, like the vivacity of impressions or ideas in virtue of which one believes them really to exist, the facility constitutive of probable relations is a content the mind does not conceive but feels. Facility and vivacity tend to go together in Hume's theorizing. When a relation between ideas is known, facility and vivacity affect are redundant to the relation and its affirmation since one is "necessarily determin'd to conceive them in that manner" (p. 95). Only when one remains free to conceive both sides of the question can assent be supposed to be a matter of feeling rather than an act of thought. In this regard, one of the most important principles of Hume's theory of understanding is that the more facile the transition from a lively perception to an idea in thought (= the stronger the relation), the more nearly the vivacity of one's conception of it (= belief in its real existence) approaches that of the lively perception itself (pp. 98–99).

Association

The effect of a facile transition between perceptions is to associate them in reflexion or thought, and it is in this association that their relation consists. With the precedent of Newtonian gravitation in mind, Hume saw fit to characterize association as "a kind of ATTRACTION, which in the mental world will be found to have as extraordinary effects as in the natural, and to shew itself in as many and as various forms" (1978, pp. 12–13). In the absence of the real connections falsely imputed to perceptions by the sophisticated and simple alike, the associative ties felt between perceptions are the source of all order and unity among them. Finally, in accordance with his scientific ideal of maximal generality and simplicity, Hume resolved all species of association into expressions of three fundamental associative principles: the contiguity of perceptions in space or time, their resemblance, and their connection as cause and effect—as "these are the only ties of our thoughts, they are really to us the cement of the universe, and all the operations of the mind must, in great measure, depend on them" (p. 662).

Natural and philosophical relations

Not all relations are constituted by facile transitions of thought. Hume designated those that are natural and those that are not philosophical relations. Since one can arbitrarily compare anything with anything else, and since no two objects admit comparison unless they have some degree of resemblance, resemblance counts not only as a natural but also as a philosophical relation; and philosophical resemblance is, in turn, the condition for other natural relations to assume a nonassociative philosophical dimension: identity, space and time, quantity (in number), quality (in degree), cause and effect, and contrariety. The crucial thing to remark here is that, except in cases of intuitive or demonstrative knowledge, philosophical relations seem to have no independent power to generate belief (vivacity), and so are parasitic on natural relations for their power to influence one's thoughts and actions. Hume made this explicit in the case of the cognitively preeminent relation, causation, for "tho' causation be a philosophical relation, as implying contiguity, succession, and constant conjunction, yet 'tis only so far as it is a natural relation, and produces an union among our ideas, that we are able to reason upon it, or draw any inference from it" (1978, p. 94).

hume's rejection of abstract ideas

Hume expressed complete agreement with George Berkeley's exclusion of abstract ideas from the explanation of general ideas and terms. The keystone of this critique of abstraction is the separability principle that Hume, like Berkeley before him, made a centerpiece of his philosophizing. According to this principle, whatever objects (perceptions) are different are distinguishable, and so separable in thought; and vice versa (1978, p. 18). So far as abstraction is concerned, this means that one cannot abstract any X from any Y unless X can be perceived and conceived even in the absence of Y. For example, because the distinction between the shape and color of a visible object fails to satisfy the separability principle, the notion that these are distinct perceptions (different abstract ideas, as Locke supposed) has to be rejected as an illusion cast by language. For while there is indeed a significative distinction to be drawn in the use of the idea of a visible object to designate, on the one hand, things resembling it in shape and, on the other hand, things resembling it in color, when the idea is considered in itself, apart from any significative use to which it may be put, its shape and color are ineluctably one.

Accordingly, differences of aspect—that is, distinctions that fail to conform to the separability principle (sometimes called distinctions of reason)—are never intrinsic to the object to which they are ascribed, but are instead always the by-product of the relations in which it stands to other objects. Thus, a globe of white marble may be found to resemble a black globe of papier-mâché, a white cube of sugar, or an oblong piece of red marble; and since resemblance is an associative relation, the facile transition from a white globe to a black globe will set up an relational dynamic in which it becomes easier to make a transition next to the idea of a blue globe, red globe, or yellow globe, than to any nonspherical white or red object. In the same way, a transition from the white globe to a white cube will make it easier to transition next to the idea of a white oblong or any other white shape than to a black globe or red oblong. It is in these divergent axes of resemblance relations, ramifying in various directions from the same object, as it were, that aspects have their basis.

Resemblance association alone does not, however, suffice to explicate general representation. Custom is equally indispensable, "If ideas be particular in their nature, and at the same time finite in their number, 'tis only by custom they can become general in their representation, and contain an infinite number of other ideas under them" (1978, p. 24). The habits instilled by frequently encountered axes of resemblance association lie in readiness to be triggered by any of the infinitely many possible stimuli (determinate, nonabstract impressions or ideas) capable of triggering it (= representational generality); and which of the many habits it happens to trigger will determine to which species a given stimulus will be recognized as belonging (i.e., under which general sort it will be subsumed or classified). For example, a single, fully determinate (nonabstract) perception of an equilateral triangle one inch in circumference can serve as a general representation of figures, rectilinear figures, regular figures, triangles, or equilateral triangles, according to which custom one uses it to represent or which custom it triggers in a particular context (pp. 21–22). Finally, with the addition of words to overcome the confusion that would otherwise result either from the capacity of the same idea to trigger any of various customs, or from the same custom to be triggered by dissimilar ideas, one arrives at Berkeley's principle "that all general ideas are nothing but particular ones, annexed to a certain term, which gives them a more extensive signification, and makes them recall upon occasion other individuals, which are similar to them" (p. 17).

space and time

Hume's treatment of abstract ideas exemplifies his general method of tracing ideas to their originating impressions; only here, where association and custom are indispensable, the experience of the operations of one's own mind (transitions of thought, the facility affect essential to associative relation, and the triggering of customs) proves to be the source of contents essential to these ideas. The abstract ideas of space and time are a case in point. Just as the shape and color of a visible object are one and indistinguishable, so, too, are extension and color. That is, the only idea one can derive from an impression of, say, uniform purple is the idea of uniform purple. To distinguish the extension from the color, one must compare the impression to others, associate them according to their resemblances, and, from the different axes of resemblances thus formed, arrive at last at an ineluctably relational conception of their difference.

Even so, to form a visual idea of space it is not enough simply to find what is resembling between purple, green, yellow, and other uniformly colored expanses, or between these and nonuniformly colored expanses. Visual space is the idea of something in which visible objects do or can appear and disappear, change their color and contour, grow, shrink, and alter their relative visible positions and situations inside, outside, alongside, adjacent, separated, above, below, right, left, in front, or behind one another. An idea with such limitless determinability is impossible except when visual perceptions are conceived of as an ordered manifold, or nexus, formed of coexistent loci (points) that preserve their relative positions to one another (their situation and relations) through any and all changes in respect of light and color ("co-existent parts dispos'd in a certain order, and capable of being at once present to the sight" [1978, p. 429]). That is, for Hume, the visual idea of space is the outcome of comparing visible objects, associating them according to their various resemblances, and forming habits when these associations are continuously reinforced, whether by frequent recurrence or some other cause. The key, as with aspects and distinctions of reason generally, is that visible space is never anything present to our eyes, prior to and independently of experience and habit, but rather something that exists only in and through the actions and affects of associative imagination (imagination in its associative capacity).

Unless this is appreciated, one cannot hope to understand how, on Hume's view, it is possible to form an idea of space common to vision and touch alike, notwithstanding the qualitative incommensurability of the objects of the two senses. For, lacking the ability to discriminate aspects immediately (nonrelationally), one can no more distinguish the extension of a tangible object from its other distinctively tactual qualities (hard or soft, smooth or rough, and wet or dry) than one can distinguish the extension of a visible object from its color. Consequently, to find visible and tangible space in any way resembling in appearance (sensible quality), one would have to find wet to be "like" yellow, red "like" softness, and so on, which of course is impossible. The locus of resemblance in virtue of which tangible and visible objects alike are supposed to instantiate the same general idea of space must instead lie in the operations the mind performs on these otherwise incommensurable appearances.

In particular, by contrast with data of the other senses, one is able to discern, and keep track of, distinctions of the finest, subtlest kind among visible and tangible appearances—distinctions sufficient in each case for association and custom to yield the abstract idea of an ordered manifold of coexistent loci (points) that preserve their relative positions to one another (their situation and relations) through any and all changes. To the imagination, then, producing and operating with two such similar manifolds feels so similar that, notwithstanding their radical qualitative disparity as appearances, it ranks them under a single, highly general idea of space. Moreover, thanks to the innumerable correlations (constant conjunctions) disclosed by experience between the objects situated in the respective imaginary spaces of each sense, one fancies that one is dealing not with distinct instances of the same general idea, but with a single, mulitsensory space, with its own, sense-divide transcending objects.

Hume's account of the origin of the idea of time differs from that of space in two principal regards: (1) whereas ideas of spatial features originate only in vision and touch, temporal ideas can be "deriv'd from the succession of our perceptions of every kind, ideas as well as impressions, and impressions of reflection as well as of sensation" (1978, pp. 34–35); and (2) whereas the manner of appearance of the spatial is defined by "that quality of the co-existence of parts," the temporal "is compos'd of parts that are not co-existent … and consequently that idea must be deriv'd from a succession of changeable objects" (p. 36). These differences aside, the psychological processes whereby ideas of the temporal are acquired are identical to those that give rise to ideas of the spatial.

From an unchanging object no idea of time can be derived "since it produces none but co-existent impressions"; only "a succession of changeable objects" can yield the idea of something composed of noncoexistent parts. But since the successiveness of, say, five notes played on the flute cannot be perceived or conceived independently of the sounds—"The ideas of some objects it [the mind] certainly must have, nor is it possible for it without these ideas ever to arrive at any conception of time" (p. 37)—any supposition that the former, as the manner of appearance of these auditory objects, is something really distinct from these objects themselves falls foul of Hume's antiabstractionist separability principle. So, just like the idea of space, that of time can only be formed by comparing distinct perceptions and associating them in resemblance relations, until a custom is produced that stands in readiness to be triggered by all and only those stimuli to which ideas of succession and duration are applied. Time, understood as an ordered manifold of determinable positions composed of indivisible, noncoexistent instants, is thus, on Hume's account, as much an amalgam of the senses and associative imagination as space.

It is in connection with time that Hume formulated another of his principles, restricting the application of ideas according to the copy principle, "Ideas always represent the objects or impressions, from which they are deriv'd, and can never without a fiction represent or be apply'd to any other" (1978, p. 37). Like the copy, separability, and other principles of concern to Hume, this principle governs only one's perception of objects in sensation, reflexion, and thought, and does not imply any restriction on one's talk of objects. Nevertheless, since perceptions are the only objects that can ever be present to one's mind, the principle restricting the application of ideas according to the copy principle restricts one's discourse to the extent that objective meaning can attach to what one says only insofar as it cashes out ideationally. And temporal ideas are a case in point: While one is free to speak of unchanging objects, no objective meaning can attach to one's discourse since one has no ideas other than those copied from fleetingly existent perceptions.

Denial of infinite divisibility

Because one's abstract ideas of space and time "are really nothing but particular ones, consider'd in a certain light" (1978, p. 34), Hume concluded that infinitely divisible space and time are impossible even to conceive. For since particular ideas are one and all copied from particular impressions, and since experience shows that one's impressions admit being divided to the point where an indivisible temporal and/or spatial minimum is reached, it follows that the ideas one derives from these impressions can never serve to conceive an infinitely divisible spatial or temporal object. (For similar reasons, Hume denied the conceivability of a vacuum in space or time.) Thus, whatever mathematicians may pretend to the contrary, the first principles of mathematics "are founded on the imagination and senses: The conclusions, therefore, can never go beyond, much less contradict these faculties" (p. 638).

Hume's Theory of Understanding

Causal relations are the centerpiece of Hume's theory of understanding. Without them, "[i]nference and reasoning concerning the operations of nature would, from that moment, be at an end; and the memory and senses remain the only canals, by which the knowledge of any real existence could possibly have access to the mind" (1999, p. 149). This is because, of all relations linking ideas to impressions, none approaches cause and effect in its power to produce belief (enliven ideas). If I see smoke coming into the room, my belief in the reality of the unseen fire causing it is as great as in the smoke itself. If the hearing of voices on the other side of the fence brings persons to mind as their cause, I not only think there are people there, I believe them really to be there. Thus, whenever I infer a cause for a given effect or an effect for a given cause, I thereby expand the scope of what for me constitutes reality beyond the immediate evidence of my senses and memory.

Although the other principles of association, contiguity and resemblance, also have power to enliven the ideas they associate with impressions, without the support of causal relations "their influence is very feeble and uncertain" (1978, p. 109). For while I can think constant relations of time and place exist beyond the scope of my senses and memory, or think an identity based on the resemblance between nonsimultaneous resembling objects, it is only insofar as causal relations underlie them that I am able to believe these relations really to exist (pp. 73–74). Thus, when it comes to explaining reasoning in matters of fact and real existence, one has no choice but to focus on the relation of cause and effect, as "the only one, that can be trac'd beyond our senses, and informs us of existence and objects, which we do not see or feel" (p. 74).

analysis of cause and effect

Hume identified four constituents crucial to the idea of cause and effect: objects relatable as cause and effect must be distinct in the sense specified in the separability principle; they must be contiguous in time and (where the objects concerned are spatial) in place; the cause must precede the effect; and there must be a necessary connection between them. Since the first three are fairly straightforward, Hume focused on necessary connection, with an eye to clarifying the idea by tracing it to its originating impression.

To understand why Hume proceeded as he did in this matter, the inherently paradoxical character of the idea of a necessary connection between distinct existents must first be taken into account. It stipulates a necessary connection between the existence of items presupposed as distinct. For example, one does not consider valleys and mountains candidates for terms of a causal relation because their necessary connection is merely conceptual, incorporated into the ideas themselves: Valleys cannot be conceived to exist in the absence of mountains and vice versa. By contrast, fire and smoke qualify as candidates for terms of a causal relation precisely because each can be conceived to exist without necessitating one to conceive the existence of the other. But there lies the rub: If to conceive them as distinct is to conceive the existence of the one to be possible even in the absence of the other, and to conceive them as necessarily connected is to conceive the existence of the one to be impossible in the absence of the other, then their combination in a single concept seems self-contradictory.

The general causal maxim

By far the most important illustration of the unintelligibility of the notion of necessary connection is Hume's analysis of the general causal maxim that everything that begins to exist must have a cause of its existence (1978, pp. 78–82). While recognition of the contingency of any determination in accordance with the maxim was a commonplace among pre-Humeans—that this specific thing causes that one—the truth of the maxim itself—that everything that comes into existence must have some cause—was taken to be an intuitively certain necessary truth, and so "one of those maxims, which tho' they may be deny'd with the lips, 'tis impossible for men in their hearts really to doubt of" (p. 79). Still, for Hume, the notion that the general maxim is a matter of knowledge rather than probability is easily refuted by a simple consideration of the concept of necessary connection itself. Its presupposition that the objects to be related in it are distinct already of itself implies the possibility that each of the objects can be conceived to exist in the absence of the other (pp. 79–80). Since even so much as a single conceivable exception is sufficient to show that a general proposition is not knowable intuitively or demonstrably, Hume concluded that the certainty of the general causal maxim is of a completely different nature, consisting not in any necessity of thought (relation of ideas) but in irresistible feeling (great force and vivacity), founded on experience and rooted in the nature of human (and much nonhuman-animal) associative psychology (pp. 82 and 172; Kant rightly recognized in this result a challenge to the possibility of metaphysics itself).

the origin of the idea of necessary connection

A source of the idea of necessary connection in the objects present to one in sensation or reflexion is precluded by the fact that all perceptions as such conform to the separability principle, and so are "distinct" in the sense implying that it is always possible to conceive any one to exist in the absence of any other, or all others. Accordingly, Hume sought the origin of the idea in the experiencing subject and the ways it regards its objects, and, in particular, in the acts and affects incident to customary transitions from impressions to ideas (1978, pp. 165–166). When one object is found by experience to constantly succeed another, a habit is formed so that when one of them is present in sensation or reflexion, it straightaway brings to mind its constant concomitant, and one not only conceives it but believes it really to exist. The facility of this transition, with the force and vivacity felt in the conception of the idea when the transition to it is from an impression, constitutes the sole and entire content of the impression-of-reflexion original of the idea of necessary connection (1999, p. 145). To be sure, a projective illusion induces one to ascribe the impression of reflexion immanent to associative imagination to the objects it considers (1978, p. 167). Nevertheless, the necessity of causes is never anything but a subjective necessity felt in the mind that considers objects, and it is in this sense that the "necessary connexion betwixt causes and effects," and "the transition arising from the accustom'd union … are, therefore, the same" (p. 165).

Since Hume defined causal necessity both as a philosophical relation, in terms of constant precedence, and as a natural relation, in terms of customary association, many interpreters have supposed that the former has a meaning and scope of application unrestricted to associative imagination. Against this, one should note that, for Hume, (1) the idea of necessary connection is an essential element in all ideas of causal relations, (2) constant precedence as such does not include an idea of necessary connection, (3) the only source from which the idea of a necessary connection can be derived is customary association, and (4) ideas can never represent any objects other than those from which they are derived.

Accordingly, the only thing that can distinguish philosophical causation from constant precedence is the addition of the idea of necessity derived from customary association, so that the necessity that "makes an essential part" of both definitions of causality is "at bottom the same" (1999, p. 160). This means that philosophical causation owes its influence on one's thoughts and actions entirely to its inclusion of a content no less bound up with conscious mind than pleasure, fear, or love; and to forget this by attempting to apply causal concepts directly to objects, apart from "that determination of the mind, which is acquir'd by custom," is to "either contradict ourselves, or talk without a meaning" (1978, p. 267).

empirical rationality

In matters of fact and real existence, reasoning, as Hume understood it, is a transition in thought from a more vivid impression or idea to a less vivid idea in which the latter is conceived with more vivacity because of the relation the transition effects between them (where facility feeling is the essence of the relation). Since, in Hume's view, the enlivening of ideas primarily depends on their association with impressions, and since causal relations far exceed any other in their ability to enliven ideas to the point where they approach the vivacity of impressions, customary transitions from impressions to ideas are at once the source of the impression originals of ideas of necessary connection and the template of all empirical reasoning. This is just to say that the one indispensable item of evidence in any inferential matter of fact or real existence is an impression of necessary connection. For, in the absence of such an impression (maximally vivid perception), there could be no belief that an idea is connected to an impression in the manner requisite to enliven it, with the consequence that the impression would not then be regarded as a reason to affirm the idea. Thus, to explicate the nature of empirical reasoning, and to distinguish reasonable (factually justified) cases of reasoning from unreasonable ones, Hume undertook an investigation into the causes of such impressions.

The nonrational basis of empirical reasoning

The principal, and the most efficacious cause, of impressions of necessary connection is frequent experience of the items connected in them in an unvarying sequence—termed constant conjunction by Hume. As the evidence for this causal connection is itself a remembered constant conjunction (between relations of constant conjunction and subsequently felt impressions of necessary connection), Hume queried whether one infers the necessary connection from experience "by means of the understanding or of the imagination; whether we are determin'd by reason to make the transition, or by a certain association and relation of perceptions" (1978, pp. 88–89).

Nothing in Hume's philosophy has received more attention than his solution to this question (usually called the problem of induction). He began by premising that if reason were responsible for the conclusion that a necessary connection exists whenever a relation of constant conjunction is found, then the inference would be grounded on the "principle, that instances, of which we have had no experience, must resemble those, of which we have had experience, and that the course of nature continues always uniformly the same " (1978, p. 89). The question thus becomes whether one's belief in this uniformity principle is itself a product of rational argument, demonstrative or probable, or whether the implicit confidence one places in it derives from a different, nonrational source (associative imagination). Demonstrative reasoning (knowledge) is easily ruled out, since "[w]e can at least conceive a change in the course of nature" and "[t]o form a clear idea of any thing, is an undeniable argument for its possibility, and is alone a refutation of any pretended demonstration against it" (p. 89). Hume next excluded probable reasoning on the ground that it cannot be the source of a belief it presupposes:

We have said, that all arguments concerning existence are founded on the relation of cause and effect; that our knowledge of that relation is derived entirely from experience; and that all our experimental conclusions proceed upon the supposition, that the future will be conformable to the past. To endeavour, therefore, the proof of this last supposition by probable arguments, or arguments regarding existence, must be evidently going in a circle, and taking that for granted, which is the very point in question.
(1999, p. 115)

Since the past can only matter to one in forming of beliefs about the present or future in probable reasoning if one already believes the future is conformable to the past, one's belief in this uniformity must have a basis other than probable reasoning. According to Hume its basis is none other than customary association, which instills in one a belief in the uniformity of nature long before one has left one's cradle and determines the reasoning of brute beasts in the same way it does humans (1999, p. 118 and 1978, p. 178).

Philosophical and unphilosophical probability

When conjunctions of perceptions are remembered to be less than constant, one's evidence of necessary connection falls short of the certainty of proof. How much credence should one accord each of the competing causes and/or effects? That is, what constitutes reasonable belief here? According to Hume the natural procedure is also the rational one: the accumulated belief (vivacity feeling) is distributed among the contrary causes or effects according to their relative constancy in past experience, subtract the lesser from the greater, and accord only so much credence (vivacity) to the latter as remains (1978, pp. 132–140). In other words, experience shows that one proportions belief in causal connections according to the constancy of the conjunction of the items concerned in them in the past and that this experience is so natural and universal that such proportioning has in all times and places been regarded as the hallmark, if not indeed the essence, of reasonable belief, or philosophical probability.

Of course, Hume was well aware that experience shows there to be many other causes of impressions of necessary connection than experienced conjunction and that these causes sometimes prevail over the evidence of experience: the ebb and flow of passions, calculations of interest and gain, laziness, hastiness, credulity, the persistence of tenets in education that have ceased to be proportioned to experience, and so on. One may be tempted to object that Hume's distinction between such unphilosophical (unreasonable or even irrational) reasoning and reasonable inferences proportioned to experience is arbitrary, since both alike are functions of feeling (vivacity transference effected by facile transitions of thought). Was he simply endeavoring to reflect linguistic practice? More likely, Hume's distinction derives from the account of the origin of impressions of necessary connection on which all causal inference depends. Experience is the natural and original cause of ideas of causal relations: It operates most constantly and steadily on the imagination and is most inseparable from the nature of that faculty (compare to 1978, p. 280). So, even in the absence of any objective or normative paradigm of rationality, nature itself, on Hume's account, sets experience at the foundation of empirical rationality.

a world in imagination

In denying that one has intuitive or demonstrative knowledge of the truth of the general causal maxim, Hume at the same time affirmed that one has another kind of certainty that everything must have a cause of its existence, arising from observation and experience (1978, p. 82) and consisting in the great vivacity of one's idea of the relation of any beginning of existence (thing, action, or state) to something precedent from which its existence follows by necessity (p. 172). The consequence is an unquestioning assumption, in any particular instance, that a cause inferred for a given effect is itself the effect of some other cause. For example, if the sight of smoke makes me think and believe that there is a fire in the hall outside, I at the same time take for granted a cause of this fire, a cause of this cause, and so on. If I reflect on this regress, I might attribute the fire to the frayed wiring I saw earlier, this to the gnawing of mice, the presence of mice in the building to the construction going on next door, the construction to the renovation plans of the new owner, the purchase of the building to the death of the old owner and the greed of the new one, and so on. But even if my theory should turn out to be mistaken (it was arson), I still remain absolutely certain of the existence of some chain of causes leading to the fire.

Since similar causal chains, with fewer or more of the blanks filled in, are taken for granted in respect of every beginning of existence, the space and time of real things demarcated by the purview of one's senses and memory comes to be dwarfed by the sphere comprised of the realities one infers to exist by means of customary association in relations of cause and effect:

'Tis this latter principle, which peoples the world, and brings us acquainted with such existences, as by their removal in time and place, lie beyond the reach of the senses and memory. By means of it I paint the universe in my imagination, and fix my attention on any part of it I please. I form an idea of ROME, which I neither see nor remember; but which is connected with such impressions as I remember to have received from the conversation and books of travellers and historians. This idea of Rome I place in a certain situation on the idea of an object, which I call the globe. I join to it the conception of a particular government, and religion, and manners. I look backward and consider its first foundation; its several revolutions, successes, and misfortunes. All this, and every thing else, which I believe, are nothing but ideas; tho' by their force and settled order, arising from custom and the relation of cause and effect, they distinguish themselves from the other ideas, which are merely the offspring of the imagination.
(p. 108)

Individuals

Hume explicated one's ideas of complex individuals (bodies and minds), both at a time (which he called simplicity) and over time (identity), as fictions resulting from failures to distinguish relations of genuine individuals from these individuals themselves. While granting that, in appearance, these fictitious individuals do not resemble genuine ones, he insisted that their feeling to the imagination in contemplating its objects is so similar in the two cases, and the associative influence of the resemblance relation so strong, that one affirms their simplicity or identity even in the face of contrary appearances (1978, pp. 202–204 and 253–254).

Hume opted for associationist explications of these ideas because he could find no way to make sense of complex individuals objectively. The only kind of simplicity one is capable of conceiving in objects (impressions and ideas) is incompatible with complexity and manifestly different from it: Perceptions may be simple, in which case there must be only one, or complex, in which case there must be more than one, but since they cannot be both one and more than one at once, the notion of a complex individual is, strictly speaking, unintelligible. The predicament is even worse when it comes to the identity of an object over time. Since "all impressions are internal and perishing existences, and appear as such" (1978, p. 194), no idea can be copied from them that is not of existents "interrupted, and perishing, and different at every different return" (p. 211). Hume took this so far as to insist that duration is inconceivable apart from succession, and so can never be represented otherwise than as a multiplicity (p. 37). To be sure, one can represent something as the same as itself at one and the same time; but this is unity, not identity (pp. 200–201). Thus, unlike simplicity, the notion of identity seems to premise a combination of unity with number that, objectively at any rate, seems unintelligible.

perfect identity

While there may be nothing objectively to distinguish the presence to consciousness of a single continuing existent from a succession of distinct qualitatively identical fleeting existents, on the subjective side there is a feeling that suffices to mark a difference:

The faculties of the mind repose themselves in a manner, and take no more exercise, than what is necessary to continue that idea, of which we were formerly possest, and which subsists without variation or interruption. The passage from one moment to another is scarce felt, and distinguishes not itself by a different perception or idea, which may require a different direction of the spirits, in order to its conception.
(1978, p. 203)

Presumably, one's mind might have been so constituted that, instead of being all but effortless, the act of successively repeating the same idea might have required great exertion and a continuous redirection of the spirits to effect it. In that case, however, the change (succession of the distinct) would be as unmistakable here as with a kaleidoscopically varying flux. Alternatively, instead of being "scarce felt," contemplating a qualitatively invariant succession might involve no feeling at all. Still, in that case, there would be nothing to induce the imagination to confuse the observation of a continued, invariant sequence of perceptions with interrupted or variable ones and Hume's account of complex individuals could not even get off the ground. Thus, the original of the idea of what Hume called perfect identity lies not merely in the objects contemplated but also in the sustained affective disposition of the imagination in successively reproducing the same idea.

the imperfect identity of body (continued and distinct existence)

Perfect identity is terminated by the first interruption or variation sufficient to necessitate a new direction of the spirits. However, "a succession of related objects places the mind in this disposition, and is consider'd with the same smooth and uninterrupted progress of the imagination, as attends the view of the same invariable object" (1978, p. 204). Since the very nature or essence of relation is facility, a succession of a single relation of ideas (facility feelings) produces the same continuity of affective disposition distinctive of a successive repetition of the same idea, and so leads one to confound them (= imperfect identity). In the case of bodies (continued and distinct existents) the principal relation is resemblance:

We find by experience, that there is such a constancy in almost all the impressions of the senses, that their interruption produces no alteration on them, and hinders them not from returning the same in appearance and situation as at their first appearance. … This resemblance is observ'd in a thousand instances, and naturally connects together our ideas of these interrupted perceptions by the strongest relation, and conveys the mind with an easy transition from one to another. An easy transition or passage of the imagination, along the ideas of these different and interrupted perceptions, is almost the same disposition of mind with that in which we consider one constant and uninterrupted perception. 'Tis therefore very natural for us to mistake the one for the other.
(p. 204)

To be sure, the identity the imagination wishes to ascribe to these appearances directly conflicts with the new direction of the spirits necessitated by their interrupted appearances. Since these interruptions "are so long and frequent, that 'tis impossible to overlook them; and as the appearance of a perception in the mind and its existence seem at first sight entirely the same, it may be doubted, whether we can ever assent to so palpable a contradiction, and suppose a perception to exist without being present to the mind" (1978, p. 206). Given that one does so virtually every moment of one's life, the question for Hume was not whether but how one reckons with the contradiction. He found the answer in the associative nature of the idea of the mind to which perceptions appear. If the mind is not, as most of Hume's predecessors believed, a real substantial unity on which perceptions essentially depend, but something conceivable only associatively, as a "connected mass of perceptions," then "there is no absurdity in separating any particular perception from the mind" (p. 207). That is, if, in accordance with the separability principle, one can conceive any perception to exist in the absence of any other or even all others, then one can conceive any perception to exist in the absence of the mind if the mind is, indeed, just another perception (namely, a complex idea produced in associative imagination).

By calling such absences interruptions in its appearance, one can attribute to the perception a reality independent of the mind. Of course, since the separability principle holds of all perceptions without exception, this is something one is capable of doing with any perception whatsoever—smells, pains, fears, desires, volitions, and thoughts no less than spatial (visible and tangible) objects. That one only exercises this conceptual capacity in the case of spatial objects is due solely to the fact that they alone exhibit the constancy requisite to produce resemblances sufficiently strong between interrupted perceptions to generate an affective disposition liable to be mistaken for perfect identity.

Even so, the distinction between the appearance and reality of spatial objects employed here is merely external (relative). Consequently, it can only disguise, not eliminate, the feature that sets up the palpable contradiction in the first place: the appearance and reality of perceptions are one and indistinguishable. Given that "all impressions are internal and perishing existences, and appear as such," the distinct, continued existence one accords to visual and tactual impressions has nothing whatsoever to do with either the reality or the appearance of these perceptions, and everything to do with operations of the imagination that considers them. That is, the only idea one is capable of forming of the identity of bodies is inseparably bound up by content with the subjective acts and affects of association imagination, and so is fictitious through and through.

In designating body a fiction, it was by no means Hume's intent to imply that one does or even can doubt its reality. For not only is the fiction rooted in fundamental principles of human nature, it is in effect self-confirming. The memories whereof ideas of bodies consist are, in general, one's most vivid ideas. Since the effect of the fiction of a continued existence is to unite the scattered memories of resembling appearances in a single idea, their vivacity feelings are pooled together in that idea, thereby producing the strongest conviction in the real existence of the continued existent thereby conceived (1978, pp. 208–209). For this reason, "[w]e may well ask, What causes induce us to believe in the existence of body?, but 'tis vain to ask, Whether there be body or not? That is a point, which we must take for granted in all our reasonings" (p. 187).

the simplicity of body: the idea of substance

Hume explicated the idea of simplicity of bodies (their individuality at a time) by means of an associative fiction closely analogous to that responsible for one's idea of their identity. The appearance and reality of one's perceptions are ignored because of the powerful influence on the imagination of its own affective disposition when it contemplates coexistent perceptions bound together by customary associations of contiguity and causality:

The connexion of parts in the compound object has almost the same effect, and so unites the object within itself, that the fancy feels not the transition in passing from one part to another. Hence the colour, taste, figure, solidity, and other qualities, combin'd in a peach or melon, are conceiv'd to form one thing ; and on account of their close relation, which makes them affect the thought in the same manner, as if perfectly uncompounded.
(1978, p. 221)

Here, too, the contradiction between one's feelings and the manifest difference in appearance between a genuinely simple object and a body—that is, the distinctness in the latter, according to the separability principle, of the color from the taste, these from the visible figure, these in turn from its tangible solidity, and so on—is too pronounced to ignore, and so must be palliated by some fiction, even if the contradiction can only be disguised thereby, not eliminated. Accordingly, we "feign an unknown something, or original substance and matter, as a principle of union or cohesion among the qualities, as what may give the compound object a title to be call'd one thing, notwithstanding its diversity and composition" (p. 221).

the imperfect identity of the mind (self and person)

In the case of the mind, one is induced to attribute identity in the face of recalcitrant appearances more by causal relations than by resemblance:

As to causation ; we may observe, that the true idea of the human mind, is to consider it as a system of different perceptions or different existences, which are link'd together by the relation of cause and effect, and mutually produce, destroy, influence, and modify each other. Our impressions give rise to their correspondent ideas; and these in turn produce other impressions. One thought chaces another, and draws after it a third, by which it is expell'd in its turn.
(1978, p. 261)

One is a witness continuously, almost from the beginning of conscious life, to impressions causing idea copies of themselves to be formed, of these ideas being the occasion of further thoughts, passions, desires, and/or volitions, these in turn causing copies of them to be formed, and so on. One's perceptions may be subject to constant change, but never, even for a moment, is a causal relation between them of some kind absent from one's purview. Since "the very essence of these relations consists in their producing an easy transition of ideas" (1978, p. 260), the facility feelings incident to contemplating an unvarying, uninterrupted series of causal relations signify the presence in one of an unvarying, uninterrupted affective disposition. The strength of this disposition, with the strength of the feeling of its resemblance to the affective disposition incident to perfect identity, leads one to attribute an identity to this system of causal relations (pp. 253–254), notwithstanding that, on the side of the appearances, one's perceptions are "a perpetual flux and movement" and nothing "remains unalterably the same, perhaps for one moment" (pp. 252–253). (Hume's account of the simplicity of the self is essentially the same as that of body [p. 263].)

Second thoughts

Hume's explication of the idea one has of oneself thus shows it to be no less fictitious than that of the idea of external objects: nothing "really binds our several perceptions together," it merely "associates their ideas in the imagination"; one never observes any "real bond" among them, one "only feel one among the ideas we form of them" (1978, p. 259). Still, by excluding all real relations from the account of the self, Hume eventually came to realize that he had no way to "explain the principles, that unite our successive perceptions in our thought or consciousness" (appendix published with the second volume [book 3 1978, p. 636] of the Treatise ). Hume saw no way out of this quandary, nor did he ever return to this topic in any subsequent work.

Skepticism

Was Hume a skeptic? Though generally reputed to be among the most extreme of skeptics, the question is not so absurd as it may seem. If a skeptic is one who doubts or even rejects the use of reason as a means of arriving at truth, then Hume was no skeptic. So long as one is guided by intuition in one's inferences in mathematics and by experience in matters of fact, "Our reason must be consider'd as a kind of cause, of which truth is the natural effect" (1978, p. 180). Furthermore, Hume recognized that many beliefs are pointless to doubt because one is literally incapable of disbelieving them or not taking them for granted in all one's reasoning, including such philosophically contentious topics as the existence of external objects and the self, space and time, and the necessity of a cause to every beginning of existence.

Consequently, many commentators have come to regard Hume's skepticism as considerably more moderate and narrowly focused than traditionally supposed. For them, what makes Hume a skeptic is that he supposed one's ineliminable beliefs skeptically unassailable not because they are founded on reasons too strong to be undermined by skeptical argument but because they are not founded on reasons at all. It is nature, not reason, that has determined one to believe certain things. Nor is reason, when understood as Hume would have one do, capable of supplying these beliefs with a rational basis immune to skeptical assault.

The problem with this view is that it focuses almost exclusively on beliefs to the neglect of their ideational contents. If Hume did indeed deem belief in the existence of body skeptically unassailable, it must also be remembered that psychological processes—the actions and affects of associative imagination—are not merely essential to the formation of the idea in which this belief is reposed but also contribute elements essential to its content (i.e., apart from which bodies are inconceivable), and limit its application accordingly. Indeed, what is perhaps most distinctive of Humean skepticism is the conceptual dimension, in which association supplies subjective-psychological surrogates, as the only way around the "contradictions which adhere to the very ideas of matter, cause and effect, extension, space, time, motion; and, in a word, quantity of all kinds" (1992, pp. 189–190).

For Hume, it is impossible even so much as to conceive these things without incorporating into one's ideas of them contents copied from impressions as irreducibly subjective as pain or disgust. What does it matter that the belief (vivacity) conferred on these ideas renders them skeptically unassailable if the ideas themselves are of such a nature that no skeptic would think to contend against them? One's reliance on associative imagination for the content of one's ideas comes at a price. If, for example, "we suppose necessity and power to lie in the objects we consider, not in our mind, that considers them," then, apart from this, "it is not possible for us to form the most distant idea of that quality" (1978, p. 167). This restriction on the scope of application of concepts so fundamental to human understanding as causation and body to the purview of a suitably constitutive experiencing mind unquestionably qualifies as a form of extreme skepticism.

varieties of hume's skepticism

When Hume himself characterized his philosophy as skeptical, he meant that it abounds with "discoveries concerning the weakness and narrow limits of human reason and capacity" (1999, p. 145). Although virtually everything in Hume's philosophy is directed to this end, among the arguments, analyses, and approaches to which he explicitly appended the term skeptical, three seem most deserving of being singled out.

Skepticism with regard to reason

After explicating empirical rationality as inferential belief proportioned to the evidence of past experience in Treatise I.iii, Hume advanced an argument in I.iv.1 to show that the result of adhering always and only to the canons of empirical rationality leads inexorably to the conclusion that "all is uncertain, and that our judgment is not in any thing possest of any measures of truth and falsity," so that "the understanding, when it acts alone, and according to its most general principles, entirely subverts itself, and leaves not the lowest degree of evidence in any proposition, either in philosophy or common life" (pp. 183 and 267–268). While most commentators consider his reasoning fallacious, Hume himself clearly deemed it impeccable and irresistible on any conception of empirical rationality, his own included (pp. 184–185). What interested him was why the argument nevertheless fails to convince. The reason he offered is that "[n]ature, by an absolute and uncontroulable necessity has determin'd us to judge as well as to breathe and feel" (p. 183).

More particularly, the argument lacks the affective force on which all relation (facility) and belief (vivacity) depend, "Where the mind reaches not its object with easiness and facility, the same principles have not the same effect as in a more natural conception of the ideas; nor does the imagination feel a sensation, which holds any proportion with that which arises from its common judgments and opinions" (p. 185). Vivacity (belief) follows facility (relation); so even if experience and custom support a certain inference, if for some reason, however trivial, facility feeling fails, vivacity will as well. And the circumstance in which understanding would subvert itself is a case in point:

We save ourselves from this total scepticism only by means of that singular and seemingly trivial property of the fancy, by which we enter with difficulty into remote views of things, and are not able to accompany them with so sensible an impression, as we do those, which are more easy and natural.… We have, therefore, no choice left but betwixt a false reason and none at all.
(p. 268)

Skepticism with regard to the senses

However impossible it may be for one in ordinary life not to believe in the distinct, continued existence of the bodies one sees and touches, only "a very little reflection and philosophy is sufficient for us to perceive the fallacy of that opinion" (1978, p. 210). Still, even if the more philosophical part of humankind recognizes this, they typically attempt to salvage the common opinion by arguing that unperceived objects correspond to perceptions that resemble them in various particulars but not their internal perishing existence. Many interpreters believe that Hume judged the philosophical view capable of sustaining skeptical scrutiny. This, however, is hard to credit in the face of his assertion that the philosophical view "contains all the difficulties of the vulgar system, with some others, that are peculiar to itself" (p. 211). If it contains all the difficulties, how can it withstand skeptical scrutiny any better? Hume's skepticism regarding the vulgar view centered on the content of the idea of a distinct, continued existence: the indispensability to it of something of the nature of an affective disposition (as is true of the idea of identity itself, this being the only means whereby the manifest differences between an interrupted or varying existence and a genuine identity can be overlooked and the two confounded).

Since the idea carries this content with it into all its applications, Hume cannot have exempted its philosophical employment from the same skeptical arguments to which he subjected its vulgar. Indeed, because the philosophical view was erected in express opposition to the verdict of the most powerful, deep-seated natural human psychological propensity to believe in the distinct, continued existence of immediately perceived visible and tangible objects (sensations), only the weakest, most ephemeral conviction can be accorded to the philosophers' objects (p. 213). Finally, Hume contended that philosophers, having no means of conceiving their would-be objects except their own perceptions, in effect do no more than "arbitrarily invent a new set of perceptions" (p. 218). If, to avoid this implication, they suppose their objects to be specifically different from everything one can conceive, the result will be an "unknown, inexplicable something … a notion so imperfect, that no sceptic will think it worth while to contend against it" (1999, p. 203).

Academic, or mitigated, skepticism

Despite the extremity of the skepticism resulting from the "deficiency of our ideas" (1978, p. 267), Hume saw fit to describe his philosophy as an exercise in "mitigated scepticism" (1999, pp. 207–211). A skepticism qualifies as such if, instead of advocating the rejection of reason in all its forms, it counsels one to reject all abstract reasoning other than mathematics, and all reasoning regarding matters of fact and experience that is not carefully and precisely calibrated to accord with the deliverances of experience.

Does Hume's own philosophical reasoning meet these criteria? It was because the empirical investigation of human understanding turns up no evidence of any other faculties besides sense and imagination that he endeavored to account for all the phenomena of perception, judgment, and reasoning (mathematics included) in terms of their operations. And it was because the only empirical source to which ideas of causal connection, substance, real existence, space, time, and the mind could plausibly be ascribed as associative imagination that he was compelled to conclude that even one's most basic, indispensable concepts of objects incorporate an ineliminably subjective element of feeling into their content (facility and vivacity). To be sure, with the understanding thus transformed (in part) into an organ of feeling, Hume's philosophy became the first to set reason on a par with pleasure and pain, passions, desires, and everything else previous philosophers had denigrated as belonging to the baser, animal part of human nature; and this may seem skeptical indeed. But since his conclusions are fully consonant with the strictures of a mitigated skepticism, he could at least be confident that his books would not be incinerated by anyone answering his call to "commit to the flames" any volume that fails to respect them.

The Will

Will is "the internal impression we feel and are conscious of, when we knowingly give rise to any new motion of our body, or new perception of our mind" (1978, p. 399). There is no implicit proposition the affirmation of which constitutes the act of volition. Volitions, for Hume, are not ideas or manners of conceiving, but feelings, felt excitations to mental or physical action. They are full-fledged perceptions (impressions of reflexion) in their own right, distinct from all others under the separability principle, capable of existing in complete isolation (p. 625). As such, they are completely indefinable: like flavors, to know volitions—to be able to form (copy) clear ideas of them—it is necessary to have the corresponding impressions; to lack the impressions is to be completely ignorant of will, to be unable to form even the most obscure idea of it.

With nothing more to be said of the will per se, Hume focused on the causes of its actuation. Nothing precludes reason from doing so since here, as always, "to consider the matter a priori, any thing may produce any thing" (1978, p. 247). Still, as a matter of fact, one finds "that reason alone can never be a motive to any action of the will" (p. 413). Convinced by reason that I am about to be devoured by a ravenous beast, for example, I would be completely indifferent to the fact, and not be provoked by this belief to any exercise of will, without the mediation of some passion in response to (caused by) the belief. Indeed, if human nature was such that being devoured by the beast was one of our fondest desires—because, say, passing through the digestive tract of a beast of that species was indispensable to reproduction—then this belief, with the passion, would excite actions to facilitate our capture. Alternately, our passionate response to the belief might be as tepid as that of a fifth grader to his or her belief regarding the result of the fifteenth of a series of long-division homework problems, so that we merely yawn at the imminent prospect of being devoured. Only passions actuate the will. Reason, according to Hume, is neither a necessary nor sufficient to do so.

For similar reasons, Hume argued that reason can never directly oppose, curb, or in any way act as a counterweight to the actuation of the will by passions. It can do so only indirectly, by giving rise to some new passion, as when it informs one that the object of one's desire is unattainable, or attainable only by a different course of action, whereupon it will produce an aversion to counter, or a desire to override, the existing passion. Consequently, when one speaks of "sweet reason" prevailing over "brute passion," it is not passionless, volitionally impotent, reason that is being invoked, but other, calmer passions. Their gentleness should not, however, be confused with weakness:

'Tis evident passions influence not the will in proportion to their violence, or the disorder they occasion in the temper; but on the contrary, that when a passion has once become a settled principle of action, and is the predominant inclination of the soul, it commonly produces no longer any sensible agitation. … We must, therefore, distinguish betwixt a calm and a weak passion; betwixt a violent and a strong one.
(1978, pp. 418–419)

Is there such a thing as a rational passion? According to Hume, no. For even though a belief can be the invariable cause of a certain passion, passions are one and all original existences: none of their features are copied from the ideas that cause them or in any way derivable from them (1978, p. 415); and even when a passion has an object—as pride takes the idea of oneself for its object and love the idea of someone else—the object remains distinct (by the separability principle) from the passion itself, and only becomes an object to it by the mediation of some feeling of pleasure, such as that given by the beauty of the beloved or the opulence of a house that has passed into one's ownership (p. 279). Passions are therefore never rational in and of themselves; and since experience shows that only passions can actuate the will, reason

is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them. … 'Tis not contrary to reason to prefer the destruction of the whole world to the scratching of my finger. 'Tis not contrary to reason for me to chuse my total ruin, to prevent the least uneasiness of an Indian or person wholly unknown to me. 'Tis as little contrary to reason to prefer even my own acknowledg'd lesser good to my greater, and have a more ardent affection for the former than the latter.
(pp. 415–416)

good/bad and pleasant/unpleasant are indistinguishable

Since reason, considered apart from whichever passions its deliverances may provoke, leaves the will indifferent, it cannot be the source of any of one's ideas of good and bad. This means that nothing propositional in character (rule, maxim, principle) can be intrinsically good or bad: carnally, spiritually, aesthetically, or in any other way. Since the only place left to look for the impression originals of ideas of good and bad are pleasant and unpleasant feelings (sensations and passions), goods and ills must all be pleasures and pains of one sort or another (1978, p. 439). Thus, for Hume, the standards one applies in all one's value judgments have their origin exclusively in pleasant and unpleasant sensations or reflexions, and neither the goals of one's actions, the deeds themselves, one's volitions to perform them, nor the character of the person who wills can be supposed good or bad either intrinsically or in relation to any rule of conduct (maxim and principle) under which they fall; they are good or bad solely by virtue of the feelings that caused them and/or the feelings they arouse.

denial of free will

The question of freedom of the will takes on a different aspect according to how a philosopher analyzes volition. If one deems will and reason inseparable, as Berkeley did, and conceives of volition as the affirmation or denial of a proposition, like René Descartes, then any external cause that necessitates one to affirm or deny will be construed as a constraint on the freedom of one's will. But if, like Hume, one distinguishes reason from will and equates volition with a nonintellectual feeling of excitation to action (impression of reflexion), then a free will, unrestrained by any necessitating cause, would be one that acted blindly and randomly, unresponsive to one's desires and heedless of one's beliefs, and so is something rather to be dreaded. Thus, from his standpoint, it is fortunate that experience shows one will not to be free, but instead to act only when necessitated to do so by some passion, be it calm or violent, beneficial or destructive, responsive or unresponsive to the deliverances of reason.

Complementing Hume's denial of free will is his analysis of causal necessity in the operations of bodies as consisting of nothing more than facile transitions of thought from one perception to its customary conjunct. For this means that there is nothing "the mind can perceive, in the operations of matter, some farther connexion between cause and effect … that has not place in the voluntary actions of intelligent beings" (1999, p. 157). All there is to causal necessity is what one experiences in every facile transition from an impression to the idea of its usual antecedent or successor. Thus, Hume's necessitarianism does "not ascribe to the will that unintelligible necessity, which is suppos'd to lie in matter," but "ascribe[s] to matter, that intelligible quality, call it necessity or not, which does or must allow to belong to the will" (1978, p. 410).

Consequently, to prove that one is in practice a necessitarian, protestations to the contrary notwithstanding, he had only to assemble reminders that one naturally and inevitably draws on one's past experience of regularities in human voluntary behavior to predict the actions of minds in precisely the same way one does to predict the actions of physical objects (1999, p. 150). To object that one encounters contrariety in the human sphere and often finds the actions of minds puzzling and unpredictable is futile since the same is true in the physical sphere as well, nor does one infer the freedom of bodies from causal necessitation because of the contrariety one finds there.

Illusions of freedom

Hume identified several reasons why one nonetheless insists on supposing oneself to be free. First, by not distinguishing the will as effect from the will as cause, one confuses two different notions of freedom. The will is free as a cause to the extent the actions of one's body and mind are subject to its control, that is, causally necessitated by it. This is the freedom one would lose if one's body or mind became unresponsive to the will or responded only to some external control. By contrast, the will is free as an effect only if its action is not necessitated by any cause, including one's own passions and beliefs, and so acts at random. The latter is the kind of freedom no one wants and, on the evidence of experience, no one has. But it is precisely this sort that matters philosophically, since the other is not only compatible with universal causal necessitation but would not be worth having otherwise.

There is also a psychological illusion of freedom implicit in the idea of necessity itself. When one perceives two objects, one does not feel a causal connection between them unless and until one observes their similarity to past constantly conjoined objects between which such a connection is felt, and then transfer the idea copied from this feeling (the reflexive impression of necessary connection) to the objects presently before one. By contrast, when one is not an observer but a performer of actions, no such reflection occurs, and consequently no connection is felt between one's perceptions (1978, pp. 408–409). For example, if I believe someone has betrayed me, and I become enraged and smash a vase against the wall, I feel no causative forces necessitating my actions; it is only afterward, when I reflect on what happened, that I recognize the necessitation of my action by the passion and the passion by my belief. Even so, I am still apt to resist the claim that in so doing my will and action were no less necessitated than a body released from a height is necessitated to fall. But apart from the fact that "there is no known circumstance, that enters into the connexion and production of the actions of matter, that is not to be found in all the operations of the mind" (p. 404), this is simply to say I can reimagine the situation so that, instead of the vase, I hurled something else or nothing at all, or that I somehow stopped myself from becoming enraged in the first place. That is not the same as supposing my volition to have been unnecessitated. It only means that, given different antecedents, different causes would have necessitated something other than the action I performed under the circumstances that actually prevailed.

The Passions

Though Hume devoted as much of the Treatise to developing a theory of the passions as he did to the understanding, the former has never attracted as much attention as the latter has. This is regrettable. Hume's theory of the passions is the mirror image of his theory of understanding: just as he was able to show the understanding to be as much an organ of feeling as of thought by explaining its most basic and important operations in terms of principles of association, so, too, by showing how surprisingly far these same principles go toward explaining the operations of the passions, he was able to reveal a deeper, underlying affinity between reason and feeling that otherwise, apart from his associationist doctrine, must remain concealed. This fundamental unity of perceptions that, to all appearances, seem disparate, or even opposed, was surely prominent in Hume's mind when he compared the place of association in the science of man to that of universal gravitation in Newtonian science of nature. One may therefore hope that Hume's theory of passions will someday receive the same amount of careful study and attention that has hitherto been reserved for other topics in his philosophy.

direct passions

Hume distinguished passions into two basic types: direct and indirect. Direct passions such as grief, joy, hope, fear, despair, and security arise immediately from some good or ill (pleasure or pain), or are themselves productive of good or ill (natural impulses such as punishing enemies and rewarding friends, as well as natural instincts such as hunger, lust, and other bodily appetites). Because their immediate cause or effect is some impression or idea of pleasure or pain, Hume could identify no role for the association of ideas in explaining their origin and only an occasional, incidental role for the association of impressions (where there is only association by resemblance). Nevertheless, he found a number of cases in which associative imagination proves crucial to enable passions already present in the mind either to commingle (or not) or to oppose one another (or not).

indirect passions

The passions of principal interest for Hume's associationist science are those he classified as indirect ideas and their associative relations are found to be causally essential to their production. The most fundamental indirect passions are pride/humility and love/hatred, but they also include ambition, vanity, envy, pity, and malice. These share a causation that takes the form of a "double relation of ideas and impressions" (1978, p. 286). Thus, an object causes a pleasure of some kind; if the object happens to be related to me by a strong enough relation, this relation of ideas (of the object to me), together with the pleasurable quality (impression) of the object, causes me to feel the resembling (because also pleasing) passion of pride (impression), whereas that same object, if productive of something unpleasant, will, given the same relation to me, cause the resembling (displeasing) passion of humility. Take away that object's relation to me, and I will feel neither pride nor humility in response to its pleasing or displeasing quality; take away its pleasing or displeasing quality and again I will feel neither passion. Consequently, pride and humility are found by experience to exist only in conjunction with an idea of myself, another object strongly related to (associated with) me, and some pleasing or displeasing quality related to (associated with) that object.

What differentiates love and hate from pride and humility is simply the object of the passion. For just as I take pride in my body or mind, or some object, insofar as it possesses some pleasing quality and has a strong relation to me—my looks, my brilliance, the imposing house I own, the beautiful painting I created, the coveted office to which I have been elected, and so on—so, too, I love or esteem someone else from precisely the same causes. Otherwise, these passions exhibit the same double relational structure.

Hume was well aware of the profusion of seeming counterexamples to this structure and spared no effort to rebut or deflect them. Still, to many, these efforts have something ad hoc about them, and Hume tends to be condemned for too rigid an adherence to theory in the face of recalcitrant phenomena. But much of this criticism may be due to a failure to appreciate the significance that double relations in question are associative in character, that is, their essence consists in facile transitions felt between impressions and ideas (1978, pp. 289, 309, 335–336, 378). This is never clearer than when, in the last three of Hume's "Experiments to Confirm This System" (pp. 332–347), he shows what seem to be counterexamples are really cases in which something interferes not with the relation considered abstractly (philosophically) but with the degree of facility felt in it, so that one or both of the relations requisite to produce an indirect passion are deprived of their associating quality, either by losing facility or because some opposing, even more facile transition prevails. Thus, when one factors in the affective dimension of Humean associationism, one can begin to appreciate Hume's evident excitement at the prospect of an explanatory principle that, for the first time, permits a systematic exposition of the human conative mind (pp. 346–347).

sympathy

The compass of one's passions would be narrowly confined to those with whom one has close personal relations if sympathy did not overcome one's indifference by communicating to one the feelings of others and enabling these to arouse one's own feelings, whether they be strangers, those known to one only by reputation, persons long dead, members of far away societies, even characters in myth. Thus, sympathy plays a key role in the operation of the passions in the wider context of human society. Regarded from Hume's perspective, however, sympathy is simply an extension of the associationist principle into the societal sphere. For, in and of itself, it is just one among species of the general associationist operation of enlivening ideas related to impressions to the point where they approach or equal the vivacity of the impressions themselves; one can call it sympathy when it increases the vivacity of an idea related to the passion felt by another to the point where it equals or approaches the original impression (1978, p. 319).

Morality

Hume's approach to morality is of a piece with the rest of his philosophy. Are there specifically moral ideas, or does moral discourse have nothing in the only object ever present to one—one's perceptions—to confer objective meaning on its pronouncements? If there are ideas, then their content must be determined by tracing them back to their originating impressions: whether they have their source in the perception of some object in sensation or reflexion (impression) or in acts of associating ideas of these objects. With the origin of moral ideas determined, enough would become evident about their place in the cognitive and/or conative economy of the human mind to permit the discovery of the fundamental principles governing moral judgment and action.

The question whether causal discourse has a basis in the objects present to one's mind came down to the question whether one experiences nothing but constant conjunctions or whether there is something more—even if that something should turn out not to be the objectively real necessary connections one's discourse might lead one to expect. In the case of moral discourse the question that was decisive for Hume regarding its objective significance is whether one's experience of good and ill is limited to passions and desires, or whether there is, in addition, a source of distinctively moral ideas.

Hume's confidence that there is more to causal discourse than experienced constant conjunction stemmed from a conviction that, given only this, reality, for one, would be restricted to the narrow compass of the senses and memory. Where morality is concerned, his confidence in its ideational foundations seems to have derived from the abundant evidence of morally motivated actions: action undertaken not for selfish reasons, from partiality for those one loves, from dread of the consequences of not performing them, or for any identifiable purpose other than the sheer morality of it. Accordingly, in tracing ideas of moral good and ill to their origin, Hume's first task was to determine whether they derive from the features or relations of the objects immediately present to one in perception or, like ideas of necessary connection, from something felt in their contemplation.

moral ideas are copied neither from objects nor their relations

For Hume, morality would count as objective if actions or things were moral or immoral prior to and independently of any course of reflection on them and, a fortiori, any feeling that arises only in the course of such reflection. For example, if willful murder were objectively immoral, then some impression embodying its immorality must exist to be copied in an idea. But what does one find when one considers such crimes objectively but a sequence of thoughts, passions, motives, volitions, and actions? The action itself is not immoral or else an avalanche would be immoral for taking the lives of skiers. That the action is voluntary does not of itself make it immoral or else lions would be guilty of immorality every time they killed. Nor does its immorality consist in the anger, greed, or other passion that determined the will, since these feelings are in themselves neither moral nor immoral. Finally, even if the course of reasoning that eventuated in the resolve to murder included an awareness that murder is wrong, its immorality, if objective, would derive not from this thought as such, but from the preexisting objective state of affairs recognized in it.

If not in the objects whereof willful murder consists, does its immorality reside in some relation of these objects discoverable by reason? Reason, as explicated by Hume, consists either in (intuitive or demonstrative) knowledge of the relations of ideas derived from objects or in belief (a vivid idea) regarding a matter of fact inferred from some other matter of fact. Against the former supposition, Hume argued that none of the knowable relations into which ideas can enter—resemblance, contrariety, degrees in quality, and proportions in quantity and number—seem capable even of distinguishing the moral from the nonmoral, much less the moral from the immoral.

If there is some other kind of knowable relation in which objective morality consists, Hume confessed to being ignorant of it. But even if there were, it would have to satisfy two conditions that seem impossible to meet. In the first place, to be a knowable yet genuinely moral relation, it could only relate two species of objects to the exclusion of all others: internal actions of the mind to external objects. Otherwise, internal actions of the mind that never eventuate in any deed could be moral or immoral, as could deeds with no mental components (thoughts and volitions). Still, so selective a relation of ideas seemed to Hume beyond the scope of what is intuitable or demonstrable by mere human minds. Second, even if such a relation did exist and were known, it would still remain for one actually to intuit or demonstrate its power to determine the will of every being possessed of a knowledge of it, divine no less than human. Since the components of the relation—knowledge and volition—are distinct perceptions, such determination could only take place via causal necessitation. Still, if Hume's analysis of causal connections shows anything at all, it is that no connection is ever intuitable or demonstrable "by the simple consideration of the objects," since "[a]ll beings in the universe, consider'd in themselves, appear entirely loose and independent of each other. 'Tis only by experience we learn their influence and connexion; and this influence we ought never to extend beyond experience" (1978, p. 466). Therefore, it seems that no moral relation can ever be knowable and vice versa.

Objective morality is also not discoverable by probable reason. Deeds objectively comprise thoughts, passions, volitions, and bodily actions. In which relation of these does its morality consist? Even if experiment revealed the existence of some hidden object, a neurochemical perhaps, that reliably tracked the distinctions one makes between the moral and nonmoral, and the moral and immoral, one's ideas of the moral and immoral could still not be originally derived from such a source since, in and of itself, neurochemicals are just as nonmoral as any of the more obvious objects concerned in moral and immoral deeds. Thus, there is nothing rationally discoverable in the objects, and expressible by an "is" or "is not," that can lead one simply by reasoning to any properly moral recognition, expressible by an "ought" or "ought not" (1978, pp. 469–470).

the subjective origin of moral ideas in internal sentiment

With objects excluded as the source of moral ideas, Hume saw no alternative but to conclude that, like ideas of cause connections, they have their origin in something one feels in the act of contemplating objects. However, the exclusion of empirical reason as their source ipso facto precludes the facility and vivacity affects immanent to associative imagination. Instead, moral ideas originate in a species of impression of reflexion that is entirely independent of imagination. This, for Hume, is not to deny that experience shows that certain processes of thought are causally essential to moral impressions; it is only to say that these processes—by contrast with the impression originals of ideas of necessary connection and identity—contribute nothing to their content. As such, moral sentiments are distinct from these processes, and from every other perception, under the separability principle, and so might conceivably have arisen in total isolation from processes of thought, as hunger and sexual appetites do, or from causes different from those experience in fact reveals. The special status of the impression of reflexion source of moral ideas therefore derives not from any special authority intrinsic to these feelings themselves—they are simply one among many other varieties of pleasure and pain—but from the unique circumstances of their causation and the special place in one's life they derive therefrom.

the causation of moral sentiments

Experience reveals that moral sentiments are aroused only in the course of reflecting on the doings of human beings, specifically the mental characteristics responsible for their voluntary actions, and of these only those most firmly rooted in a person's character: the most efficacious and enduring characteristics of the identity that constitutes an individual human mind. This causation explains why moral feeling weakens or vanishes altogether when one contemplates actions not considered to be tests of character, because, say, their performance was prompted by an uncharacteristic whim, an excusable misjudgment regarding the facts, fever, disease, medicinal side effects, or involuntarily through some unavoidable external cause.

The causal structure of moral feeling resembles that of the indirect passions of pride/humility and love/hate in that it involves a double relation of impressions and ideas: an object (idea) related to a person (another idea) is the subject of some pleasant or unpleasant feeling (impression) that, because of the relation between the objects, gives rise to its resembling (pleasing or displeasing) moral feeling (another impression). Indeed, with the proviso that the causes of moral feelings are restricted to mental characteristics strongly related to the person, the pleasures and pains that arouse moral feelings prove to be precisely the same ones that arouse feelings of pride/humility in oneself and to love/hate toward others (1978, pp. 574–575), so that moral feelings may be regarded as "nothing but a fainter or more imperceptible" (p. 614) variety of these passions themselves.

There are, however, two further features of the causation of moral sentiments that distinguish them from indirect passions:

Moral feeling requires a general point of view

The indirect passions are invariably partial for or against their particular object (oneself or another). Moral sentiments, by contrast, tend to be felt only when "we fix on some steady and general point of view" in which one abstracts from "our situation of nearness or remoteness, with regard to the person blam'd or prais'd, and … the present disposition of our mind" (1978, pp. 581–582). Moral feelings are at their strongest (remembering that, for Hume, the strength of a sentiment is often inversely proportional to its violence) when the character of the person is viewed from the standpoint where it

appears the same to every spectator. … And tho' such interests and pleasures touch us more faintly than our own, yet being more constant and universal, they counter-ballance the latter even in practice, and are alone admitted in speculation as the standard of virtue and morality. They alone produce that particular feeling or sentiment, on which moral distinctions depend.
(p. 591)

From a personal perspective, one may be far more moved by the moral perfections of a best friend than by those of some moral giant of the past like Gandhi. Still, this delight is not moral sentiment. That feeling can arise only when one brackets out one's personal feelings for the person, whereon one cannot help feeling a far stronger feeling in contemplating Gandhi than one's friend (though this is no guarantee that, when it comes to determining the will, one's moral sentiments will be strong enough to prevail over nonmoral ones).

Moral feeling requires sympathy

Since reason is impotent to determine the will and useless by itself to distinguish moral right from wrong, moral action is wholly at the mercy of moral sentiment. But if moral sentiments can arise only through their association with other pleasures or pains (in the context of a double relation of impressions and ideas), how is it possible for moral feeling to arise if it requires one to regard persons from a general point of view in which abstraction is made from everything determinative of one's present affective disposition? Hume's answer is that the capacity to remain affectively engaged depends on one's ability to sympathize with the persons one considers from a general point of view. Thanks to this societal variety of association, one continues to feel pleasure or displeasure from the consideration of the mental qualities rooted in the characters of persons one considers impartially. Since this permits the condition for the double relation of impressions and ideas requisite to produce moral sentiment is met, one then has only to contemplate the character from the general point of view requisite for moral sentiment for the pleasant or unpleasant feelings produced by sympathy to cause a corresponding pleasant or unpleasant moral sentiment.

virtue and vice

Another way in which the impression of reflexion originals of moral ideas and those of ideas of necessary connection are alike is that, despite being subjective (felt only in contemplating objects), they are illusorily projected onto the objects contemplated and treated as though they were properties of the objects themselves (1978, pp. 167, 224–225). In the case of moral feelings, the objects that take on moral attributes are the mental characteristics whose agreeableness or disagreeableness cause moral feelings, whereon they count as virtues or vices: "taste … gives the sentiment of … vice and virtue … [and] has a productive faculty, and gilding or staining all natural objects with the colours, borrowed from internal sentiment, raises, in a manner, a new creation" (1998, p. 163).

Hume's typology of virtue of and vice

Hume distinguished four (nonexclusive) types of virtue:

(1) Mental qualities immediately agreeable to their possessors, such as skill, greatness of mind, cheer, equanimity in the face of adversity, and courage

(2) Qualities immediately agreeable to others, such as tact, delicacy, wit, and good manners

(3) Qualities useful to their possessors, such as intelligence, industriousness, skill, patience, and perseverance

(4) Qualities useful to others, such as gratitude, faithfulness, reliability, and charity

The pleasure one takes in these mental qualities in and of themselves is enhanced by the moral pleasure with which one responds to them, thereby adding a moral beauty to their original, nonmoral beauty. Similarly, the displeasure occasioned by their contraries is augmented by moral displeasure, and to their natural ugliness moral repugnancy is added. This, in turn, increases the effects these qualities have on other passions, above all the pride or love and humility or hatred felt on their account. Indeed, as mental qualities capable of stirring moral sentiments in one when considered with sympathy from a general point of view, pride/humility and love/hate now take on a moral value in their own right. Thus, if the pride another takes in his or her character is the effect of real virtues and proportionate to them, our contemplation of his or her pride (a pleasing quality) can only add to the pleasure we derive from contemplating the pleasing qualities in which he or she takes pride, whereas if his or her pride is a perverse pleasure deriving from morally repugnant mental qualities, his or her feelings about him- or herself can only increase the contempt we feel in contemplating those qualities.

Hume seems convinced that many of the qualities commonly deemed virtuous in his and other societies would not be considered virtues, or even be deemed vices, if people could overcome the distorting influences that prevent them from attaining a truly impartial, sympathetic perspective on human characters. Religious education, for example, can condition one to regard as virtuous the asceticism of monks, the fanaticism of zealots, or the credulity of the faithful—qualities of mind that would otherwise be certain to strike one as both repellant in themselves and harmful (1998, pp. 146–147). But, for Hume, the fact that miseducation, harsh conditions of life, and other factors can lead people to mistake virtues for vices and vices for virtues no more makes the one really the other than the fact that people are often influenced to discount or ignore past experience in their reasoning means that there is no real difference, rooted in human nature, between good and bad empirical reasoning. Nothing—interest, expediency, or serendipity—can make disagreeable or harmful mental qualities be, or appear to be, anything other than they really are. Nevertheless, outside influences may intervene to prevent one from attaining the constancy and universality of perspective, and/or the sympathetic engagement, requisite to bring one's moral sense to bear on such disagreeable or harmful qualities and respond to them with the contempt they would otherwise naturally and universally inspire.

Of course, even if human nature ensures that universal agreement regarding virtue and vice is possible in the abstract, things are different when it comes to judging, in any particular instance, whether an action issued mainly from moral, immoral, or amoral motives, and in which proportions. Hume was keenly aware, in his capacity as philosopher no less than that of essayist or historian, that motives for particular actions can be complex and obscure, even to the agent, and that agreement in one's judgments regarding the morality may be impossible owing to differences in experience, education, access to information, and individual mental abilities. Matters are further complicated by the fact that moral sentiments must compete with other passions for influence on the wills of agents and the hearts of judges. Nonetheless, even if human nature cannot always reveal what one ought to do in each particular instance, Hume still deemed moral sentiment a universally valid standard accessible to anyone concerned to know what kind of person he or she ought to be; and, in this regard, moral sentiment serves as a dependable guide in moral decision making and judgment.

artificial virtues

Institutions such as property, contracts, government, intergovernmental relations, and marriage must exist before the virtues of justice (the rightful possession of property), promise-keeping, allegiance, treaty-keeping, and chastity are even possible. A first precondition is that everyone, or nearly everyone, realize that they stand to benefit when every member of society, selves included, adheres to the rules requisite for these institutions to exist and flourish. Second, each person's recognition of their interest in everything that promotes universal adherence to these rules leads them to take pleasure in those mental qualities of persons that contribute most to making them just, faithful keepers of promises, loyal subjects, good treaty-makers and -keepers, and good husbands or wives. Only then, when reflecting on these pleasing qualities of persons from a general point of view, will each person's moral sense respond to these qualities with its own distinctive feeling, whereupon qualities originally prized only from self-interest at last come to elicit one's admiration as virtues.

What prompted Hume to classify these and other virtues as artificial rather than as natural, even though their origin in a recognition of the utility of certain mental qualities is no different from many natural virtues? Justice, for example, presupposes property, which, as an institution founded on a tacit convention, is, in Hume's view, thoroughly artificial, and in that sense unnatural. Although there is possession, property in the strict sense (as carrying an obligation not to hinder possession) does not yet exist in a state of nature, where something is mine if, by strength or wit, I can get it and keep anyone else who wants it from taking it. When goods are either too plentiful or too scarce, and generosity is confined to one's closest relations, there is no interest or intrinsic virtue to inhibit one from taking anything one wants from anyone else, even if one's need for it is not desperate. But when goods are neither too plentiful nor too scarce, a condition in which everyone takes whatever they want whenever they can prevents anyone from enjoying the benefit of secure possession of the goods they want or need for future use. The resulting dissatisfaction with the existing state of things thus creates an openness to change.

The problem is that it is not in my interest to leave anyone else in secure possession of my goods if I cannot be assured that the other person will do the same for me. This impasse is broken only with the establishment of a tacit convention, based on self-interest, of leaving others in possession of their goods provided they are prepared to leave one in possession of oneself. Moreover, since it is in the interest of all to be able to exchange some of the goods one has for others one needs or desires more, the convention of secure possession must also provide means whereby the goods of another can become one's own and vice versa, so that secure possession is transferred with them. Thus, through the artifice of tacit conventions, property in goods, over and above their mere possession, first comes into existence.

The reason that Hume classified justice in matters of property as an artificial virtue is that there is nothing about any good one desires to possess or retain, considered in and of itself, that can convey to one an idea of it as property. Property is unintelligible apart from established conventions, and conventions, however universal, tacit, and informal, are always artificial. For this reason, Hume denied that there is any natural interest or virtue in justice. Only after one has been inducted into the mysteries of the institution of property can one arrive at a recognition of one's interest in universal adherence to the rules requisite to maintaining it and so, a fortiori, come to prize as virtues the mental qualities most conducive to that interest. The same is true of every other virtue that presupposes human institutions founded on tacit conventions secured by a recognition of self-interest: contracts, laws, public offices, government, and so on. So, even though artificial virtues are no less genuine or powerful expressions of moral sentiment than natural ones, Hume deemed them as unnatural to one's species as speaking English or paying in British currency.

Religion

One cannot be certain what Hume's actual views were with regard to belief in God. He was quite clear that he was not a Christian, and he seems to have regarded all religions as expressions of superstition, vestiges from less enlightened times that might (or might not) someday be superseded or wither away. However, Hume was also somewhat skeptical concerning contemporary atheistic conceptions. Matters are further complicated by the times in which he lived. Apart from legal sanctions (after a period of relative openness, new censorship laws began appearing in the late 1730s), a person's career prospects, social position, and tranquillity would be put in jeopardy by too open an expression of views liable to be construed as impious. For anyone unconcerned with mundane matters, zealous in the cause of atheism and enlightenment, desirous of being the focus of controversy, or sufficiently naive, these impediments might not matter. But Hume was not such a person. He was too worldly wise and fond of his place in society to bring down on himself the consequences of a frontal assault on the religious beliefs and institutions dear to the overwhelming majority of humankind. So, while many would agree with contemporary charges that his views on such matters as the general causal maxim and freedom of the will are implicative of atheism, Hume himself always professed the contrary (1978, pp. 409–10, 633n; 1999, pp. 160–164 1745/1967). And though his writings on religion seem to lead inexorably to the conclusion that a rational faith in God or revealed religion is an impossibility, he never ceased to proclaim that "the existence of a DEITY is plainly ascertained by reason" (1992, p. 280).

What is one to make of Hume's claims that his philosophy is consistent with, even supportive of, a rational belief in God? If these pretensions had been sincere, he would have had every reason to advertise the opinion, as other philosophers did who employed skepticism to humble reason to elevate faith. But one finds no evidence of this in his philosophizing beyond occasional brief asides, which seem too casually thrown out for one not to suspect that they are there merely to provide cover for his skeptical forays. It seems unquestionable that Philo, rightly regarded as Hume's principal mouthpiece in the Dialogues concerning Natural Religion, was not serving in that capacity when he declared that "[t]o be a philosophical skeptic is, in a man of letters, the first and most essential step towards being a sound, believing Christian" (1992, p. 292). Hume's actual skepticism points in a different direction, as a close examination of the arguments in his writings on religion reveals.

the idea of god

Hume professed agreement with Locke and other anti-innatists that the idea of "an infinitely intelligent, wise, and good Being" has its origin in one's "reflecting on the operations of our own mind, and augmenting, without limit, those qualities of goodness and wisdom" (1999, pp. 97–98). Nevertheless, he also maintained that the attempt to realize this definition in an idea is fraught with difficulty. Not only is "the capacity of the mind … limited, and can never attain a full and adequate conception of infinity" (1978, p. 26), even large numbers are representable only by means of the power of multiplying ideas, and, like all powers, rests ultimately on custom (pp. 22–23). The case of qualitative superlatives such as wisdom and goodness is even more problematic, for, finite or infinite, they "are not, like quantity or number, susceptible of any exact mensuration, which may be the standard" (1992, p. 281). In addition, Hume devoted the greater part of the Dialogues to showing that the empiricist definition of the divine founded on qualities of the human mind can never provide one with an idea remotely adequate to underwriting the conception of God featured in the discourse of philosophical theologians. Had he been bolder, he might also have applied to the case of God the implications of his associationist explications of the ideas of power and efficacy (necessary connection), substance, identity over time, the simplicity of complex beings, personhood, and reason. For their result is to show that these ideas are all inseparably bound up by content with the actions and affects of associative imagination, and so cannot be used to comprehend anything that exists prior to and independently of idea-enlivening, transition-facilitating. Therefore, it is ironic (no doubt intentionally so) that Hume ended up on the same side as the most pious monotheists (represented by Demea in the Dialogues ) in insisting on the incomprehensibility of the nature of the divine.

a priori arguments for the existence of god

The ontological argument for the existence of God advanced by many philosophers before Hume depends on treating existence as a property of God in the same sense in which goodness, wisdom, power, and other attributes are ascribed to the nature of divinity, and, moreover, like them, a necessary property. Hume argued against the first part of the thesis by denying that existence can ever be conceived of as a property, be it of God or any other being. For to be able to do so, existence would have to be a distinct idea in its own right, capable of being combined with other ideas to form a complex idea, and there is no such idea in one's possession. Nor is the real existence attributed to God when, instead of merely conceiving him to exist, one believes him actually to exist, any new addition to the idea either, "When I think of God, when I think of him as existent, and when I believe him to be existent, my idea of him neither encreases nor diminishes" (1978, p. 94).

Even if there was an idea of real existence one could conjoin with one's idea of God, one still could not suppose it to apply necessarily, "Nothing that is distinctly conceivable implies a contradiction. Whatever we conceive as existent, we can also conceive as non-existent. There is no being, therefore, whose non-existence implies a contradiction. … The words, therefore, 'necessary existence' have no meaning; or, which is the same thing, none that is consistent" (1992, p. 251). If it is objected that God might in fact be a necessary existent even if existence does not attach to God of necessity in the idea one's feeble mind is able to form of divinity, the reply is that the same may be true of the unknown nature of any object, sensible objects included. The point is that one can never have reason to include existence in one's idea of God as a necessary attribute.

a posteriori arguments for the existence of god

Insofar as Hume's explications of ideas such as cause and effect show them to be bound up by content with the actions and affects of associative imagination, the scope of their application is limited to the purview of appropriately constituted conscious minds. Consequently, in order to even to raise the question whether experience provides any justification for inferring the existence of God, Hume had first to set aside these explications. This should not be forgotten when trying to assess the true nature and scope of his critique of a posteriori theistic reasoning.

cosmological arguments for the existence of god

Many philosophical theists employ the general causal maxim to argue from the fact that something exists that some first cause must exist as well, since the supposition of an infinite regress of causes implies that the whole chain of causes and effects would lack a cause or reason for existing, and this is inconsistent with the maxim. Hume regarded such reasoning as fallacious:

[T]he uniting of these parts into a whole, like the uniting of several distinct countries into one kingdom, or several distinct members into one body, is performed merely by an arbitrary act of the mind, and has no influence on the nature of things. Did I show you the particular causes of each individual in a collection of twenty particles of matter, I should think it very unreasonable should you afterwards ask me what was the cause of the whole twenty. This is sufficiently explained in explaining the cause of these parts.
(1992, pp. 252–253)

arguments from design

Though given a pass in the Treatise and elsewhere in Hume's corpus, Hume subjected the design argument for the existence of God to critical scrutiny in section 11 of Enquiry concerning Human Understanding, "Of a Particular Providence and of a Future State." The discussion takes the form of a dialogue between Hume and a paradox-loving skeptical friend who imagines what Epicurus might have said in his defense if brought before a tribunal on charges of impiety and endangering the state because of his denial that religion (the existence of God and of a providence and future) can be established "upon principles of reason" (1999, p. 189).

For the sake of argument, Epicurus grants that the order, beauty, and wise arrangement everywhere observed in the universe cannot have resulted from material causes alone, so that the point at issue is what kind of author(s) can be inferred from the work according to the canons of empirical reasoning. Since the cause is something that has never been observed by any mortal, and since the given effect (the totality of design in nature) is so singular as to afford no basis for determining the general characteristics (species) of its cause, Epicurus maintains that one has no choice here but to subject one's reasoning to the "maxim, that where any cause is known only by its particular effects, it must be impossible to infer any new effects from that cause, since the qualities, which are requisite to produce these new effects along with the former, must either be different, or superior, or of more extensive operation, than those which simply produced the effect, whence alone the cause is supposed to be known to us" (1999, p. 196n).

This means that one must incorporate into one's conception of the cause the abundant empirical evidence of disorder, ugliness, indifference to human welfare, and the unjust distribution of talents, goods, and fates. So, even with the concession that matter and motion are insufficient to account for the world, the cause one is warranted in inferring from the effect as one empirically finds it falls far short of the superlative, benevolent intelligence proponents of the design argument claim to be able to infer.

In the Dialogues this line of argument is deepened and expanded, even while Hume maintains the pretense that the design argument suffices to prove the existence of a deity and fails only when it comes to providing insight into the nature of that deity (like Kant after him, Hume suggests, in the Dialogues [dialogue 5], that empirical reasoning would need to be supplemented by a priori if this want were to be made good). It is impossible here to do justice to this splendid work, possibly the finest philosophical dialogue since Plato. Suffice it to say that its conclusion is "that the causes or causes of order in the universe probably bear some remote analogy to human intelligence" (1992, p. 291).

What this means becomes clearer in the light of Philo's observation in dialogue 7 that intelligence is just one of four known causes of order in the world and that the same claim of a remote analogy with the cause(s) of order in the universe can, with equal reason, be made for instinct (a bird's design of its nest), generation (of offspring by animals), and vegetation (seeding). Since even an atheist can admit that, in this highly attenuated analogical sense, it is proper to think of the cause of order in the world as similar to intelligence—and possibly to many other, as yet unknown principles of order as well—nothing of any consequence seems to be warranted by the conclusion reached in the Dialogues. Indeed, it is no wonder that Hume has Philo argue that the difference between atheists and certain theists is merely verbal (1992, pp. 280–281).

Nor does Philo deny that, among the unknown principles of order in the world, some may be inherent in matter itself, such that over vast periods of time, a minute probability that the motions of particles will eventuate in the production and replication of stable, orderly forms must eventually be realized (1992, pp. 244–247). Since other principles of order, known and unknown, may themselves be explicable in terms of principles inherent in matter, even the modest conclusion reached at the end of the Dialogues is put in jeopardy by this concession—"So dangerous is it to introduce this idea of necessity into the present question! And so naturally does it afford an inference directly opposite the religious hypothesis!" (p. 1992, p. 253) Since Hume elsewhere made no secret that he embraced necessity in precisely this sense, one cannot help wondering if the neo-Epicurean excursus in Dialogues (dialogue 7) was not intended to remind his reader of Hume's own explication of cause and effect, to the end of rejecting all causal reasoning in matters of religion—as happens overtly in Enquiry concerning Human Understanding :

It is only when two species of objects are found to be constantly conjoined, that we can infer the one from the other; and were an effect presented, which was entirely singular, and could not be comprehended under any known species, I do not see, that we could form any conjecture or inference at all concerning its cause. If experience and observation and analogy be, indeed, the only guides which we can reasonably follow in inferences of this nature, both the effect and cause must bear a similarity and resemblance to other effects and causes, which we know, and have found, in many instances, to be conjoined with each other. I leave it to your own reflections to pursue the consequences of this principle.
(1999, p. 198)

reason and revelation

Is it ever rational to accept the truth of revealed religion? Those who answer affirmatively typically point to prophecies fulfilled and miracles performed. Since such evidence comes to nearly all of us by way of oral or scriptural testimony, Hume asked if conditions exist under which one could rationally credit reports of prophesies and miracles and, if so, whether any revelation has ever met these conditions. The key to his reasoning in this matter is the recognition that human testimony on any topic owes whatever authority it has in the eyes of reason to the same source causal inferences do: past experience. Finding there to be a fairly constant conjunction between the facts as reported by witnesses and as ascertained by other means, one has only to hear or read (have an impression of) a report for one's mind not only to think (form an idea) of the event reported but also to believe it to the extent (enliven the idea to the degree) warranted by experience. For, besides lending authority to testimony in general, experience also teaches one that particular reports are more or less credible depending on the reporter, the circumstances under which the report is given and received, and the event reported itself. If a report falls short of maximum credibility on any of these counts, then reasonable persons must refuse to give it the same credence they accord to empirical beliefs founded on a frequently encountered, perfectly constant conjunction, having the certainty of proofs.

Reports of miracles are intrinsically suspect because the events they report are, by their nature, the least creditable. As defined by Hume, an event is miraculous only if it meets two conditions: it contradicts a law of nature and does so "by the particular volition of the Deity, or by the interposition of some invisible agent" (1999, p. 173n). A law of nature is a causal sequence found by constant experience to be invariable, and so has the highest authority empirical reason can confer. Accordingly, to determine whether one can rationally credit any report of a miracle, one must follow the procedure empirical reason prescribes whenever two beliefs regarding matters of fact are found to conflict: deduct from the empirical support of one of the beliefs the amount of support possessed by the other and, if any support remains, accord it only so much credence as that remainder warrants; otherwise, discount it or (if the beliefs have equal support) refrain from believing either way. However, when one does this, one finds that

no testimony is sufficient to establish a miracle, unless the testimony be of such a kind, that its falsehood would be more miraculous, than the fact, which it endeavours to establish: And even in that case, there is a mutual destruction of arguments, and the superior only gives us an assurance suitable to that degree of force, which remains, after deducting the inferior.
(p. 174)

Since it is impossible that experience could ever give one reason to regard the falsehood of any report of miracles as more improbable than the falsehood of a law of nature, even the most credible testimony imaginable could not win one's acceptance if belief were always proportioned to experience. The same is true of prophecies, for these are simply a species of miracle ("If it did not exceed the capacity of human nature to foretel future events, it would be absurd to employ any prophecy as an argument for a divine mission or authority from heaven" [1999, p. 186]). Thus, one's acceptance of revealed religion can never possess the rational authority to which belief proportioned to the evidence of experience can alone lay claim.

religious belief

Having established that one has no clear idea of God to underwrite religious discourse nor any rational basis for religious belief, Hume devoted the remainder of his discussion of miracles, as well as other writings ("The Natural History of Religion" [1757] most notably), to examining the nature and causes of religious belief. The upshot is that one believes in God and accepts the proofs of purported revelation from the same causes that lead one to form other beliefs not proportioned to experience (unphilosophical probabilities): failure to clarify one's ideas or to ascertain the existence of ideas corresponding to one's words; education; credulity; self-interest; the influence of the passions; eloquence and other appeals to imagination that detach reason from its moorings in experience; the errors and exaggerations that tend to creep in with each new telling of a story; and so on. The implication is that, however widespread a religious belief may be, it is not imposed on one by human nature, and so is not irresistible in the way that belief in causes, continued distinct existents, and the self are.

Hume did not deny that religious belief can ever be agreeable or useful, either for the individual or society, but he did seem to think that, in the forms it actually takes—especially when vitiated by superstition or enthusiasm—it is neither. For example, in two essays, "Of Suicide" and "Of the Immortality of the Soul" (written in 1755 but published posthumously in 1777 [though a French edition appeared in 1770]), he argued that there is no rational or moral basis for the prohibition of the former or for belief in the latter. Still, his single most important philosophical contribution to the effort of combating the deleterious influence of religion is the example set by his theory of morals: It illustrates how universally valid moral standards can be understood nontheologically, in terms exclusively of natural sentiment and artificial interest.

See also Aesthetics, History of; Alembert, Jean Le Rond d'; Bacon, Francis; Beauty; Berkeley, George; Causation: Metaphysical Issues; Causation: Philosophy of Science; Colors; Common Sense; Cosmological Argument for the Existence of God; Determinism, A Historical Survey; Determinism and Freedom; Diderot, Denis; Enlightenment; Human Nature; Induction; Kant, Immanuel; Locke, John; Newton, Isaac; Perception; Philo Judaeus; Reason; Reid, Thomas; Revelation; Rousseau, Jean-Jacques; Skepticism, History of; Smith, Adam; Space; Virtue and Vice; Volition.

Bibliography

works by hume

Four Dissertations. London: Printed for A. Millar, 1757.

The Philosophical Works of David Hume. 4 vols. Edited by T. H. Green and T. H. Grose. London: Longmans, Green, 1875.

The Letters of David Hume. 2 vols. Edited by J. Y. T. Grieg. Oxford, U.K.: Clarendon Press, 1932.

New Letters of David Hume. Edited by Raymond Klibansky and Ernest Campbell Mossner. Oxford, U.K.: Clarendon Press, 1954.

A Letter from a Gentleman to His Friend in Edinburgh (1745). Edited by Ernest Campbell Mossner and John V. Price. Edinburgh, Scotland: Edinburgh University Press, 1967.

A Treatise of Human Nature. Edited by L. A. Selby-Bigge. Oxford, U.K.: Clarendon Press, 1978.

The History of England, edited by William B. Todd, Indianapolis: Liberty Classics, 1983.

Essays Moral, Political, and Literary. Edited by Eugene F. Miller. Indianapolis, IN: Liberty Classics, 1987.

Writings on Religion. Edited by Antony Flew. La Salle, IL: Open Court, 1992.

The Clarendon Edition of the Works of David Hume. Edited by Tom L. Beauchamp, David Fate Norton, and M. A. Stewart. New York: Oxford University Press, 1998–.

An Enquiry concerning the Principles of Morals: A Critical Edition. Edited by Tom L. Beauchamp. New York: Oxford University Press, 1998.

An Enquiry concerning Human Understanding. Edited by Tom L. Beauchamp. New York: Oxford University Press, 1999.

A Treatise of Human Nature. Edited by David Fate Norton and Mary J. Norton. New York: Oxford University Press, 2000.

works about hume

Àrdal, Páll S. Passion and Value in Hume's "Treatise". Edinburgh, Scotland: Edinburgh University Press, 1966. A detailed textual analysis of Hume's theory of the passions.

Baier, Annette. A Progress of Sentiments: Reflections on Hume's Treatise. Cambridge, MA: Harvard University Press, 1991. An authoritative, highly persuasive vision of the Treatise as the onerous progress of reason toward self-comprehension, which it finds in society.

Baillie, James. Hume on Morality. London: Routledge, 2000.

Beauchamp, Tom L., and Alexander Rosenberg. Hume and the Problem of Causation. New York: Oxford University Press, 1981. An attempt to defend Hume's views on induction and causation against contemporary views.

Bricke, John. Mind and Morality: An Examination of Hume's Moral Psychology. New York: Oxford University Press, 1996.

Capaldi, Nicholas. Hume's Place in Moral Philosophy. New York: Peter Lang, 1989.

Flew, Antony. David Hume: Philosopher of Moral Science. Oxford, U.K.: Basil Blackwell, 1986.

Fogelin, Robert L. Hume's Skepticism in the Treatise of Human Nature. London: Routledge and Kegan Paul, 1985. Aspires to restore Hume's skepticism to a status equal, and complementary, to his naturalism, both in epistemology and in morals.

Forbes, Duncan. Hume's Philosophical Politics. New York: Cambridge University Press, 1975.

Garrett, Don. Cognition and Commitment in Hume's Philosophy. New York: Oxford University Press, 1997. One of the finest books on Hume to date.

Gaskin, J. C. A. Hume's Philosophy of Religion. 2nd ed. Atlantic Highlands, NJ: Humanities Press International, 1988.

Haakonssen, Knud. The Science of a Legislator: The Natural Jurisprudence of David Hume and Adam Smith. New York: Cambridge University Press, 1981.

Harrison, Jonathan. Hume's Theory of Justice. Oxford, U.K.: Clarendon Press, 1981.

Laird, John. Hume's Philosophy of Human Nature. London: Methuen, 1932. A classic.

Livingston, Donald W. Hume's Philosophy of Common Life. Chicago: Chicago University Press, 1984. Maintains that Hume adopted the approach of the social historian even in epistemology.

Mackie, John L. The Cement of the Universe: A Study of Causation. Oxford, U.K.: Clarendon Press, 1974.

Mackie, John L. Hume's Moral Theory. London: Routledge and Kegan Paul, 1980. A projectivist reading of Hume's sentimentalism, with a keen analysis of his account of virtue.

Miller, David. Philosophy and Ideology in Hume's Political Thought. Oxford, U.K.: Clarendon Press, 1981.

Mossner, Ernest Campbell, ed. "Hume's Early Memoranda, 1729–1740." Journal of the History of Ideas 9 (1948): 492–518.

Mossner, Ernest Campbell. The Life of David Hume. 2nd ed. Oxford, U.K.: Clarendon Press, 1980.

Norton, David Fate, ed. The Cambridge Companion to Hume. New York: Cambridge University Press, 1993.

Norton, David Fate. David Hume: Common-Sense Moralist, Sceptical Metaphysician. Princeton, NJ: Princeton University Press, 1982. Contains an excellent account of Hume's relation to Frances Hutcheson and examines other influences on Hume.

Owen, David. Hume's Reason. New York: Oxford University Press, 1999. Corrects many misconceptions, especially regarding Hume's conception of deductive reason. An outstanding work.

Passmore, John. Hume's Intentions. 3rd ed. London: Duckworth, 1980.

Pears, David. Hume's System: An Examination of the First Book of His Treatise. New York: Oxford University Press, 1990. Effects a balance between Hume's empiricism and naturalism by correlating the first to a theory of meaning and the second to a theory of truth.

Philips, D. Z., and Timothy Tessin, eds. Religion and Hume's Legacy. New York: St. Martin's, 1999.

Read, Rupert, and Kenneth A. Richman, eds. The New Hume Debate. New York: Routledge, 2000.

Russell, Paul. Freedom and Moral Sentiment: Hume's Way of Naturalizing Responsibility. New York: Oxford University Press, 1995.

Smith, Norman Kemp. The Philosophy of David Hume. London: Macmillan, 1941. Instigated the move away from skeptical readings of Hume.

Snare, Francis. Morals, Motivation, and Convention: Hume's Influential Doctrines. New York: Cambridge University Press, 1991.

Stewart, M.A., and John P. Wright, eds. Hume and Hume's Connexions. University Park: Pennsylvania State University Press, 1995.

Stove, D. C. Probability and Hume's Inductive Scepticism. Oxford, U.K.: Clarendon Press, 1973.

Strawson, Galen. The Secret Connexion: Causation, Realism, and David Hume. New York: Oxford University Press, 1989.

Stroud, Barry. Hume. London: Routledge and Kegan Paul, 1977. Presents Hume as advancing a theory of human nature in which the traditional conception of man as rational animal is overturned.

Townsend, Dabney. Hume's Aesthetic Theory: Taste and Sentiment. London: Routledge, 2001.

Tweyman, Stanley, ed. David Hume: Critical Assessments. 6 vols. London: Routledge, 1995.

Tweyman, Stanley, ed. Hume on Miracles. Bristol, U.K.: Thoemmes, 1996.

Waxman, Wayne. Hume's Theory of Consciousness. New York: Cambridge University Press, 1994.

Waxman, Wayne. Kant and the Empiricists: Understanding Understanding. New York: Oxford University Press, 2005. Emphasizes the affinity between Hume and Kant as exponents of a psychologistic method of explicating concepts.

Whelan, Frederick G. Order and Artifice in Hume's Political Philosophy. Princeton, NJ: Princeton University Press, 1985.

Wilson, Fred. Laws and Other Worlds: A Humean Account of Laws and Counterfactuals. Dordrecht, Netherlands: D. Reidel, 1986.

Wayne Waxman (2005)