Reid, Thomas (1710–1796)

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Thomas Reid was the founder of the Scottish "Common Sense" school of philosophy. A contemporary and critic of David Hume, he is best known for his staunch defense of common sense and trenchant opposition to the "way of ideas," the theory that the immediate objects of perception and other cognitive acts are always internal images or ideas, not external physical objects. His views exerted a good deal of influence until the mid-nineteenth century or so, when they began to be eclipsed by absolute idealism, pragmatism, and other philosophical movements, but they have been the subject of renewed interest from the 1970s on.

After being educated at Marischal College in Aberdeen, Scotland, Reid served for fifteen years as a parish minister in nearby New Machar. In 1752 he was appointed professor at King's College in Aberdeen, where he taught mathematics, physics, and philosophy, among other subjects. He tells us that in his youth he believed nearly the entire philosophy of George Berkeley but that a reading of Hume's Treatise of Human Nature (17391740) convinced him (by carrying Berkeley's philosophy to its logical conclusions) that there must be some original defect in it. Reid identified this defect as the theory of ideas, which he went on to challenge in college lectures, meetings of the Aberdeen Philosophical Society, and two books. In 1764 he published his first major work, An Inquiry into the Human Mind on the Principles of Common Sense, in which he set forth his reasons for opposing the theory of ideas and offered an alternative theory of how we gain knowledge by means of the various senses. In the same year he accepted the chair in moral philosophy at Glasgow, succeeding Adam Smith. He lectured there until 1780, when he resigned to prepare his last two major works: Essays on the Intellectual Powers of Man (1785), devoted to the contributions of perception, memory, reason, and other cognitive powers to human knowledge, and Essays on the Active Powers of the Human Mind (1788), devoted to the nature of action, will, freedom, and morality.

This article provides a synopsis of Reid's main views more or less in the order in which he presented them in his three published books: the Inquiry (abbreviated as Inq.), the Intellectual Powers (abbreviated as IP), and the Active Powers (abbreviated as AP). Numbers separated by a period refer to chapter and section numbers in the Inquiry and to essay and chapter numbers in the two volumes of Essays.

Critique of the Theory of Ideas

Almost alone among the great modern philosophers, Reid espoused a direct realist theory of perception. He repudiated the assumption that what is immediately present to the mind is never an external thing, but only an internal image, impression, representation, or (to use the most common eighteenth-century term) idea. Ideas were usually conceived of as mental entities that existed only as long as the mind was aware of them. Reid found the theory of ideas to be taken for granted in the work of most of his philosophical predecessors, including René Descartes, Nicolas Malebranche, Antoine Arnauld, John Locke, Berkeley, and Hume. Some of these philosophers (for example, Descartes and Locke) were realists, believing that ideas are caused in us by physical objects existing outside the mind. Others (notably, Berkeley) were idealists, repudiating the existence of a world outside the mind and believing that the things we call physical objects are simply bundles of ideas. In either case, we are cut off from direct perception of the physical world, either because there is no physical world to be perceived, or because our perception of it is indirectnot strictly perception at all, but inference based on what we do perceive, namely, ideas.

Reid makes at least three important points against the theory of ideas. First, the arguments in favor of the theory are weak and without cogency; second, the theory does nothing to explain how perception is possible; third, the theory stands in the way of our knowing or even being able to conceive of the physical world.

One of the arguments for the theory of ideas that Reid singles out for criticism is a version of the argument from perceptual relativity. Hume had claimed that the "universal and primary opinion of all men" that they perceive external objects directly is "destroyed by the slightest philosophy," offering the following argument in section 12 of the Enquiry concerning Human Understanding : "The table, which we see, seems to diminish as we remove further from it; but the real table, which exists independent of us, suffers no alteration. It was therefore nothing but its image which was present to the mind." Hume's argument may be cast into the following syllogism: (1) What I see diminishes in magnitude as I retreat from it; (2) the table itself does not diminish in magnitude as I retreat from it; (3) therefore, what I see is not the table itself (but only an image or idea).

Reid contends that Hume's premises are true only if we restate them as follows (IP 2.14, p. 182): (1) What I see diminishes in apparent magnitude as I retreat from it; (2) the table itself does not diminish in real magnitude as I retreat from it; (3) therefore, what I see is not the table (but only an image or idea).

The real magnitude of an object (for example, the edge of a table) is an intrinsic property of it, measured in feet or inches, whereas the apparent magnitude of an object is a relation between the object and a perceiver (or his vantage point), measured by the angle the object subtends at the eye. Reid takes the terminology of "real" versus "apparent" from the astronomy of his day; it is not necessarily implied that there is anything illusory about apparent magnitude. It is easy to see that apparent magnitude varies with the distance between object and perceiver (objects subtending smaller angles when further away) whereas real magnitude does not. Once we record these facts correctly, as in Reid's version of the syllogism, we see that the conclusion of the argument does not follow from the premises. Moreover, Reid would resist the thought that if O has greater apparent magnitude when seen from p than when seen from p', that is because it presents a larger image to the observer at p than to the observer at p'. Apparent magnitude is a strictly dyadic relation, involving only the object and the perceiver (or his vantage point) and no third thing such as a mental image.

Reid's second point against the hypothesis of ideas is "that ideas do not make any of the operations of the mind to be better understood" (p. 184). Ideas had been thought necessary to explain how we perceive things that are distant, remember things that are past, or imagine things that do not exist at all, but Reid argues that all such explanations are worthless. They presuppose that ideas themselves can somehow be of the remote, the past, or the nonexistent. But if ideas can do that, what prevents the simple idealess acts of perceiving, remembering, and imagining from doing it as well? Moreover, our ability to be aware of ideas themselves is no less mysterious than our ability to be aware of things that are not ideas.

It is as difficult to conceive how the mind perceives images in the brain as how it perceives things more distant. If any man will shew how the mind may perceive images in the brain, I will undertake to shew how it may perceive the most distant objects: for if we give eyes to the mind, to perceive what is transacted at home in its dark chamber, why may we not make these eyes a little longer-sighted? (Inq. 6.12, p. 121)

Reid's third point against the theory of ideas is "that the natural and necessary consequences of it furnish a just prejudice against it to every man who pays a due regard to the common sense of mankind" (p. 185). Chief among these consequences is that if we do not simply see or touch external objects, it becomes necessary to prove their existence by arguments. Descartes, Malebranche, and Locke all tried to muster such arguments, but none of the arguments is convincing. Reid thus thinks that skepticism about the material world is a built-in consequence of the theory of ideas. By contrast, if what we see and touch are not ideas but things in the external world, as in Reid's own view, this source of skepticism is eliminated.

Sensation and Perception

A sensation is an event that occurs in a sentient subject when he or she smells a rose or tastes a fig. It lacks figure and extension and other qualities of bodies, being entirely mental. Reid calls sensations "principles of belief," by which he means that when we have a sensation and attend to it, we cannot help believing that it exists, that a subject of it exists (ourselves), and that some external object (for example, some quality in the rose) exists as its cause.

Reid is among the first to distinguish between sensation and perception. He explains this distinction as follows:

Thus, I feel a pain ; I see a tree : the first denoteth a sensation, the last a perception. The grammatical analysis of both expressions is the same: for both consist of an active verb and an object. But, if we attend to the things signified by these expressions, we shall find, that in the first, the distinction between the act and the object is not real but grammatical; in the second, the distinction is not only grammatical but real. The form of the expression, I feel pain, might seem to imply, that the feeling is something distinct from the pain felt; yet, in reality, there is no distinction. As thinking a thought is an expression which could signify no more than thinking, so feeling a pain signifies no more than being pained. What we have said of pain is applicable to every other mere sensation. (Inq. 6.20, pp. 16768)

When I perceive a tree, there is an object (the tree) apart from my act of seeing, but when I have a sensation, there is no object apart from the act of sensing. As he defines sensation in the Intellectual Powers, it is an act of the mind "which may be distinguished from all others by this, that it hath no object distinct from itself" (IP 1.1, p. 36). That formulation is ambiguous: Does an act of sensing have itself for its object, or does it have no object at all? Although Reid's language often suggests the former option, his proposal that being pained is the model for all sensation suggests the latter option. If we take Reid in the latter way, he is a precursor of "adverbial" theories of sensation, such as were developed by C. J. Ducasse and Roderick Chisholm two centuries later: to have a sensation of red is not to sense something, but is simply to sense somehow "redly," as the adverbial theory styles it.

Some critics of Reid have thought that his sensations are simply ideas under a new name, but there are important differencesespecially if he holds an adverbial theory rather than a theory that divides sensation into act and object. If sensing required its own special objects, the argument from perceptual relativity against direct realism could be reinstated. The mountain that looks blue from a distance and green from close up would do so by generating first blue and then green sensory objects in my mind, and these variously colored objects would have to be distinct from the unchanging mountain. They would displace the mountain itself as my object of direct awareness. But Reidian sensations do not have objects to get in the way of direct perception of external things.

Although sensations do not have objects, they can become objects for us, in the sense that we can know through proper attention what sorts of sensations we are having. Indeed, Reid thinks that if we attend carefully to our sensations, we can know perfectly what they are like and can scarcely make any mistake about them. Yet typically we pay so little attention to them that we become almost oblivious to them; they serve as mere cues or signs from which our minds leap instantly to other things that they signify.

Our apprehension of that which sensations signify is perception. Reid's official characterization of perception involves three elements: conception, belief, and immediacy:

If, therefore, we attend to that act of our mind which we call the perception of an external object of sense, we shall find in it these three things:First, Some conception or notion of the object perceived; Secondly, A strong and irresistible conviction of its present existence; and Thirdly, That this conviction and belief are immediate, and not the effect of reasoning. (IP 2.5, p. 96; cf. Inq. 6.20, p. 168)

Note that this definition makes no mention of sensation. Although Reid says that sensation generally serves as the trigger for the conception and belief involved in perception, perception proper is just conception plus immediate belief. Reid thinks it possible that perception should occur in the absence of sensation, and he holds that there is one variety of human perception that actually does occur without any characteristic sensation: namely, the perception of visible figure. Reid thus deemphasizes the role of sensation in perception in a way that some contemporary theorists (for example, James J. Gibson) would applaud. By the same token, however, his threefold definition may strike others as leaving out precisely that by which a genuine perception of a snake in the path ahead is distinguished from the conception and immediate belief in it one may form as the result of a friend's warning. Here Reid's views may gain in plausibility if we reckon his "conception" as something like what Bertrand Russell called knowledge by acquaintance. It is not necessarily the exercise of a concept in mere thought.

Reid's Nativism

Reid thought that much of what he found alarming in Hume's philosophy stemmed from Hume's adherence to the empiricist maxim that we have no ideas or notions that are not derived from previous impressions or sensations. It is by this principle that Hume was led to conclude that we have no legitimate notions of objects existing unperceived, of causal connections amounting to more than constant conjunctions, and of a self that is the subject of various mental operations. Reid sought to overthrow Hume's philosophy by undermining its foundations, and for this purpose he tackled the empiricist principle head-on. He pointed to a notion that he thought Hume would surely concede that we possessthe notion of extension, or being spread out in spaceand contended that this notion lacks a proper Humean birthright in our sensations. If it were once acknowledged that not even so uncontroversial a notion as extension can be extracted from our sensations or impressions, Reid thought, the way would be open for recognizing the legitimacy of other notions with no sensory origin, such as the ideas of agency, self, and an external world.

To back up his contention that the notion of extension is not derived from sensation, Reid offers a thought experiment he calls his experimentum crucis (Inq. 5.6 and 5.7, pp. 6572). He asks us to imagine a being furnished with a progressively richer array of sensations, beginning with those caused by the prick of a pin, advancing to more complex sensations such as those caused by the pressure of a blunt object against his or her body, and culminating with the sensations accompanying the motion of his or her limbs. He asks at each step in the series whether those sensory materials would suffice to give a being who reflected upon them a conception of extension, and his answer is no. Positively, Reid's doctrine is that the conception of extension is innatenot in the sense that we have it from birth, but in the sense that it is triggered in us by certain sensations from which it could never have been derived from any process of abstraction or ratiocination. We are enabled to form the conception of extended things only because we are innately programmed to do so.

For further light on the import of Reid's nativism, we may restate it in terms of the threefold classification of natural signs he offers in sections 4.2 and 5.3 of the Inquiry. Reid first divides signs into the artificial and the natural. In the former class, the connection between sign and thing signified is established by compact or convention, as with the words of human language. In the latter class, the connection between sign and thing signified is established by nature, as with smoke and fire and other cases of effect and cause. Reid then further divides natural signs into three classes. In the first class, the connection between sign and thing signified is "established by nature, but discovered only by experience" (Inq. 5.3, p. 59), as in the example of smoke and fire already given. In the second class, the connection is "not only established by nature, but discovered to us by a natural principle, without reasoning or experience" (Inq. 5.3, p. 60).

Reid thinks that certain features of the human countenance are signs in this sense of thoughts and other mental states. For example, an infant is innately disposed to read a smile on its mother's face as a sign of approval without having to learn this connection through experience. Unless there were a basic repertoire of natural signs of this second class, Reid believes, the signification of artificial signs could never be agreed upon or learned. Finally, in the third class are those signs "which, though we never before had any notion or conception of the thing signified, do suggest it, or conjure it up, as it were, by a natural kind of magic" (Inq. 5.3, p. 60). Not only is the connection between sign and thing signified innately programmed into our constitution (as with signs of the second class), but also the very notion of the thing signified is innate in the sense that it is in no way derivable by abstraction from any of our sensations. Reid believes that the tactile sensations to which we respond with conceptions of extended bodies are natural signs belonging to this third class.

Reid takes his nativism to afford an answer to an argument for skepticism he finds embodied in the combined philosophies of Berkeley and Hume. He formulates the argument as follows (Inq 5.8, p. 75): (1) We can have no conception of anything but what either resembles or is deducible from our sensations; (2) nothing resembles or is deducible from sensations but other sensations; (3) therefore, we can have no conception of anything but sensations.

If the argument were correct in both its premises, it would follow that we cannot even conceive of, let alone have knowledge of, a world lying beyond our sensations. Reid thinks the second premise is correct, and he credits Berkeley with having made it evident. But he thinks the first premisewhich states in Reid's language Hume's principle that all our ideas are copied from precedent impressionsis false. "That we have clear and distinct conceptions of extension, figure, motion, and other attributes of body, which are neither sensations, nor like any sensation, is a fact of which we may be as certain, as that we have sensations" (Inq. 5.8, p. 76).

The Mechanics and Geometry of Vision

More than half of the Inquiry is devoted to vision, which Reid regards as the noblest of the senses. It informs us of the properties of objects far distant, such as the sun and the moon, and it can disclose in a glance the figure of a cathedral, whose delineation by touch would be the work of a lifetime.

Reid provided solutions to a number of puzzles about vision that lie today within the province of cognitive science rather than philosophy. For example, why do we see things upright despite having inverted retinal images of them? To explain this, Reid appeals to the law that an object will be seen in the direction of a straight line drawn from the point of retinal stimulation through the center of the eye and into ambient space. Why do we normally see objects single despite having two retinal images of them, yet under certain circumstances see them double? Reid's answer appeals to the law of corresponding retinal points: If rays from an object fall on points of the two retinas lying at equal distances and directions from their centers, the object will be seen as single, but otherwise as double.

One of Reid's more remarkable findings is that the visible figures of objects are governed by a non-Euclidean geometry. Reid believed that sight by itself (before we have learned any correlations with touch) informs us only of the two-dimensional spatial features of objects. Although the objects we see are at a distance from us (pace Berkeley), the eye is incapable of making any discriminations of depth. To an eye placed at the center of a sphere and looking out, great circles on the surface of the sphere (whose outward curvature is invisible to the eye) must appear as straight lines, and every figure seen by the eye must have the same geometrical properties as some figure drawn upon the sphere. In consequence of this, Reid argued that the geometry of visibles is what we would nowadays classify as a Riemannian geometry. A visible triangle, unlike a triangle perceived by touch, always has an angle sum at least slightly greater than 180 degrees, and no two visibly straight lines are ever strictly parallel.


Essay III of the Intellectual Powers is devoted to memory. Reid characterizes memory as "an immediate knowledge of things past" (IP 3.1, p. 253). There are two senses in which this is true. First, the object of memory is the very thing or event formerly perceived, not some present idea or simulacrum of it (Inq. 2.3, p. 28). Second, the knowledge one has by memory of this past object is noninferential; it does not rest on any reasoning from premises. Memory is thus like perception for Reid in involving both the conception of an object and an immediate belief in its existence; but it differs from perception because the object is, and is believed to be, past. Reid is severely critical of Hume's attempt to distinguish imagining, remembering, and perceiving solely in terms of the force and vivacity of their objects.

Reid criticizes Locke's view that memory is what constitutes personal identitythat person A is identical with person B who existed in the past if and only if A remembers what B did. He insists that memory is the evidence of personal identity, rather than that in which it consists (IP 3.4, p. 265). He also presents the famous "brave officer" objection to Locke's theory, courtesy of his friend George Campbell: Suppose a man who has become a general late in life remembers capturing the enemy flag as a young officer; that as an officer he remembered being flogged as a boy for robbing an orchard; and that as a general he no longer remembers being flogged as a boy. It follows from Locke's theory that the general both is and is not the same person as the boy (IP 3.6, p. 276).

Conception and Abstraction

Essays IV and V of the Intellectual Powers are devoted to conception and abstraction. Conception, the most basic operation of the mind, is "that operation of the understanding which the logicians call simple apprehension," that is, the apprehension of a thing without any belief or judgment about it (IP 4.1, p. 295). "Judgment can be expressed by a proposition only, and a proposition is a complete sentence; but simple apprehension may be expressed by a word or words, which make no complete sentence" (IP 6.1, p. 408). The objects of conception expressed by words or subsentential phrases are either individuals or universals. What Reid calls conception should not be confused with conceptualizationthat is, subsuming something under a conceptfor the latter is judgment, and conception is more basic than judgment.

Reid holds that all the operations of our minds except sensation have objects distinct from themselves. "He that conceives, must conceive something" (IP 4.1, p. 311), and the same goes for perception and memory. It is a distinctive feature of conception, however, that its objects need not exist: "it is not employed solely about things which have existence" (IP 4.1, p. 310).

On this point, Reid is sometimes seen as a precursor of Alexius Meinong, who held that there can be cognitive relations to the utterly nonexistent and that a thing therefore need not exist in order to stand in relations. Meinong's view strikes many as paradoxical. Yet Reid makes it look like one more piece of common sense or, at any rate, a consequence of two pieces of common sense (IP 4.1, p. 311): (1) I can conceive of a centaur; (2) no centaur exists; (3) therefore, I can conceive of what does not exist. In case anyone objects that the truth in premise 1 is simply that I can conceive of the idea of a centaur, which does exist, Reid is ready with a reply: I know the difference between conceiving of a centaur and conceiving of the idea of a centaur, and I can assure you that I am doing the former rather than the latter (IP 4.2, p. 321).

Reid's view that the objects of conception may be nonexistent has an interesting application to the problem of abstract ideas, which pitted Locke against Berkeley and Hume. On this topic, Reid writes, "Mr. Locke and his two antagonists have divided the truth between them" (IP 5.6, p. 394). Locke saw clearly "that the power of forming abstract and general conceptions is one of the most distinguishing powers of the human mind," but he did not see "that this power is perfectly irreconcileable to his doctrine concerning ideas." Berkeley and Hume "saw this inconsistency; but instead of rejecting the hypothesis of ideas, they explain away the power of abstraction."

To see how Locke and his critics "divided the truth between them," consider the following inconsistent triad of propositions:

  1. We are sometimes aware in thought of the general and the abstractin Reid's terminology, we have the power of forming abstract and general conceptions.
  2. We can only be aware of what exists: "in all of the operations of the understanding, there must be an object of thought, which really exists while we think of it" (IP 4.2, p. 312).
  3. General entities have no existence: "every thing that really exists is an individual" (IP 5.6, p. 393).

As Reid saw it, Locke accepted both 1 and 2 and was therefore driven to deny 3, despite his affirmation of it elsewhere. He posited "abstract general ideas," such as the infamous image of a triangle that is neither isosceles nor scalene, as merely generic entities existing in the mind. Berkeley and Hume, on the other hand, both accepted 2 and 3, and were thus led to reject 1. Not believing that entities such as Locke's merely generic triangle could exist even in the mind, they denied that we are ever aware of general entities. Thus were born their attempts to explain how we can think generally (for example, in proving propositions about all triangles) by means of ideas that are particular.

Reid's novelty is to deny proposition 2, which he castigates as one of the prejudices giving rise to the theory of ideas. It led all three of his predecessors in the British Empiricist tradition to affirm that the immediate object of awareness, in conception as well as in perception, must be an idea. By denying 2, Reid was enabled to uphold both 1 and 3, thus collecting together the truths his predecessors had divided between them.

First Principles

Essay VI of the Intellectual Powers contains an extensive and important treatment of what Reid calls first principles. A first principle is a self-evident propositiona proposition that is evident to us without need of any reasons to support it. Like Aristotle, Reid thinks that our knowledge must ultimately rest on first principles, for without them we would be faced with an infinite regress of supporting propositions. He may therefore be classified as an epistemological foundationalist. Reid believes there are first principles both of necessary and of contingent truths. The first principles of necessary truths include axioms of logic, mathematics, grammar, metaphysics, and morals. The first principles of contingent truths include principles pertaining to the deliverances of consciousness (Reid's term for introspection), perception, memory, inductive reasoning, and others of our faculties.

In Reid's enumeration of the first principles of contingent truths, there is a subtle ambiguity that greatly affects how his epistemology is to be interpreted. Here is how he formulates Principle 1, which gives us the first principle(s) regarding consciousness: "First, then, I hold, as a first principle, the existence of every thing of which I am conscious" (EIP 6.5, p. 470). Putting this in terms of truth rather than existence, he might just as well have said that he holds, as a first principle, the truth of every proposition to which consciousness testifies. The ambiguity in Principle 1 may then be brought out by the following two ways of symbolizing it, where "Cp" is short for "I am conscious that p":

1.1 It is a first principle that (p)(Cp -> p). (It is a first principle that for any proposition p, if I am conscious that p, then p.)

1.2 (p)(Cp -> it is a first principle that p). (For any proposition p, if I am conscious that p, then it is a first principle that p.)

The difference between the formulations is this: 1.1 says that it is a first principle that all the deliverances of consciousness are true. In other words, 1.1 gives us one general proposition as first principle. 1.2, on the other hand, says that each of the deliverances of consciousnesswhich may include propositions such as I am now in pain are themselves first principles. So 1.2 gives us many particular propositions as first principles. A similar ambiguity holds in regard to the first principles of perception and memory.

How should Reid's first principles be understoodas general or particular? Perhaps the best overall interpretation of Reid's epistemology is provided by the particularist construction. At the very least, his epistemology must be understood as recognizing particular first principles even it recognizes general first principles as well.

If Reid's first principles are construed in the particularist way, he is not only a foundationalist in his epistemology but also (in one important sense) an externalist. Externalists hold that there are sources or factors that give a subject knowledge even if the subject does not know anything about how the factors work or whether they are reliable. On the particularist construction of Reid's principles, the mere fact that a proposition is a deliverance of perception, memory, or consciousness suffices to make that proposition evident (and thus, in favorable circumstances, known). To know that there is a tree over there, for example, one need only have a perception of a tree. It is not necessary for the subject to know anything about the reliability of sense perception, which may be a matter to which he has never given any thought. On the generalist construction of the principles, by contrast, the subject would presumably have to know that the general principles are true in order for knowledge of particular propositions to arise in accordance with them. In other words, he would have to know his faculties are reliable before they could be sources of any other knowledge. That puts an obstacle in the way of knowledge that skeptics might claim to be insurmountable.

It may be useful to summarize by drawing together the various things Reid has to say in response to skepticism about the material world. First, what skeptical philosophers profess cannot be believed and is not believed even by skeptics themselves. This is a point that Hume famously admitted, and it may be questioned what force it has against the truth or reasonableness of the skeptic's position. Second, the argument that we cannot even conceive of a material world is answered by Reid's nativism, according to which we are endowed by our constitution with conceptions of extended external objects.

Third, the argument that knowledge of the external world must be based on problematic inferences from our ideas is undercut by Reid's attack on the theory of the ideas. Fourth, the position of the "semiskeptic," who says we can be certain about the deliverances of our consciousness but not about anything else, is objectionably arbitrary. For who can prove that consciousness never errs? And what reason is there to believe the deliverances of consciousness that is not a reason for believing the deliverances of our other faculties as well? (Inq. 5.7, p. 71).

Finally, the position of the total skeptic, who refuses to accept the deliverance of any faculty unless its reliability is proven in advance, is irrefutable (Inq. 5.7, p. 71; cf. IP 6.5, p. 480). We cannot show that he or she is wrong without assuming something he or she would question. But perhaps, for all that, we may know that he or she is wrong, if Reid's externalist approach to epistemology is correct.

Causation and Freedom

As noted above, Reid thinks we have many conceptions, such as that of a self or subject of mental operations, that we could not have on Humean principles. Among them is the conception of active power, or real efficacy in bringing about changes, to which Reid turns in his third book. He thinks we obtain a clear conception of such power when we are conscious of our own activity in bringing something about by an act of will. Active power is exercised only by agents or substances, not by events, so in the strictest sense of causation, only agents are causes for Reid. When we speak of one event causing another, Reid tells us, it would be more proper to speak of events related by lawful sequence or a relation of sign and thing signified.

That we sometimes act freely (or that we possess "moral liberty") is, according to Reid, a natural conviction, comparable to our belief in a material world. In the Active Powers, he offers three arguments that we really do possess such liberty. The first is based on the "naturalness" of our conviction in regard to it, the second on the notion of moral responsibility, and the third on our ability to secure ends by prosecuting a long series of means.

Reid rejects accounts of moral liberty such as those of Hobbes and Hume, who seek to make liberty compatible with determinism. He would reject Hume's suggestion that I did A freely if I did A as a result of willing to do it and would have done otherwise if I had willed otherwise. In a universe in which my willing was itself the end of a causal chain stretching back to the Big Bang, the conditions of this definition might be satisfied, yet I would not, according to Reid, have acted freely. It is a further requirement of liberty that my willing not have been determined by antecedent events in that way. But that is not to say that my willing must be random or uncaused. On the contrary, in a case of free action, it is caused by me, the agent. In this way Reid brings his theory of agent causation into his account of liberty, attempting to escape the dilemma that has determinism as one horn and arbitrary uncaused acts of will as the other. Reid believes that every event has a cause, but he holds that the cause of an event need not be another eventit may be an agent.

Agent-causation theories of human action inspired by Reid began to undergo a revival during the last third of the twentieth century, finding advocates in Roderick Chisholm and Richard Taylor, among others. Such theories offer a tantalizing glimmer of hope for resolving old problems yet face formidable problems of their own. If I am the cause of my willing to do A, mustn't there be such an event as my causing the willing? If so, what is the cause of that event? If it is nothing, we have fallen back on the randomness horn and violated Reid's professed belief that every event has a cause. If it is a further event, we are back on the horn of determinism. If it is the agent, we have taken the first step of an infinite regress in which I am the cause of my willing A, the cause of my causing of my willing A, and so on, ad infinitum.

Moral Philosophy

Reid is often considered to be a member of the moral-sense school of philosophy, insofar as he holds that moral notions and moral determinations are the product of a moral faculty or sense. He insists, however, that the employment of the term sense is accurate only with the proviso that a sense can deliver judgments as well as feelings. In opposition to Hume, he holds that "moral approbation implies a real judgment" (AP 5.7, pp. 457481), capable of being true or false, and is not merely an expression of feeling like "Hurrah!" (It must be said, however, that his criticisms of Hume sometimes convert the supposedly noncognitivist view he is attacking into a subjectivist form of cognitivism). In further opposition to Hume, he holds that reason is not merely the slave of the passions but has a real role to play in the selection of ultimate ends of action (AP, 5.3).

Reid also opposes another kind of view that sometimes goes under the rubric of moral-sense theory: the view that moral properties are analogous to secondary qualities, as in the suggestion that for an action to be right is for it to arouse favorable moral emotion in those who contemplate it. Reid protests that such accounts abolish the necessity of moral principles. It is necessary, according to him, that actions of certain types are right but contingent that they produce whatever effects they do in those who contemplate them (IP, 6.6, pp. 494495). On the whole, Reid's views probably bear less resemblance to moral-sense theories than they do to the intuitionism of G. E. Moore. Much of what Reid says about right anticipates what Moore said about good : that it is indefinable, that we understand what it is by an original power of the mind, and that our moral faculty provides us with first principles about which types of acts are right and which wrong.

See also Aristotle; Arnauld, Antoine; Berkeley, George; Causation; Chisholm, Roderick; Common Sense; Descartes, René; Ducasse, Curt John; Geometry; Hobbes, Thomas; Hume, David; Introspection; Locke, John; Malebranche, Nicolas; Meinong, Alexius; Moore, George Edward; Nativism, Innatism; Russell, Bertrand Arthur William; Smith, Adam.


works by reid

The Works of Thomas Reid, D. D., edited with notes by Sir William Hamilton. 2 vols. 8th ed. Edinburgh, U.K.: James Thin, 1895. Reprint Hildesheim: Georg Olms, 1983.

Essays on the Active Powers of Man, edited by Baruch Brody. Cambridge, MA: MIT Press, 1969.

An Inquiry into the Human Mind on the Principles of Common Sense, edited by Derek R. Brookes. Edinburgh, U.K.: Edinburgh University Press, 1996. Reprint University Park: Pennsylvania State University Press, 1997.

Essays on the Intellectual Powers of Man, edited by Derek R. Brookes. University Park: Pennsylvania State University Press, 2002.

The Correspondence of Thomas Reid, edited by Paul Wood. University Park: Pennsylvania State University Press, 2002.

works about reid

Alston, William P. "Thomas Reid on Epistemic Principles." History of Philosophy Quarterly 2 (1985): 435452.

Barker, Stephen F., and Tom L. Beauchamp, eds. Thomas Reid: Critical Interpretations. Philadelphia: Temple University Philosophical Monographs, 1976.

Broadie, Alexander. "Reid Making Sense of Moral Sense." Reid Studies 1 (1998): 516.

Cummins, Phillip. "Reid's Realism." Journal of the History of Philosophy 12 (1974): 317340.

Dalgarno, Melvin, and Eric Matthews, eds. The Philosophy of Thomas Reid. Dordrecht, Netherlands: Kluwer, 1989.

De Bary, Philip. Thomas Reid and Skepticism: His Reliabilist Response. London: Routledge, 2002.

Daniels, Norman. Thomas Reid's Inquiry: The Geometry of Visibles and the Case for Realism. Palo Alto, CA: Stanford University Press, 1974.

Falkenstein, Lorne. "Reid's Account of Localization." Philosophy and Phenomenological Research 61 (2000): 305328.

Gallie, Roger. Thomas Reid and "The Way of Ideas." Dordrecht, Netherlands: Kluwer, 1989.

Grave, S. A. The Scottish Philosophy of Common Sense. Oxford, U.K.: Clarendon Press, 1960.

Haldane, John. "Thomas Reid: Life and Work." American Catholic Philosophical Quarterly 74 (2000): 317344. This issue contains eleven articles devoted to Reid.

Immerwahr, John. "The Development of Reid's Realism." The Monist 61 (1978): 245256. This issue is entirely devoted to Reid and includes thirteen articles on his philosophy.

Lehrer, Keith. Thomas Reid. London: Routledge, 1989.

McKitrick, Jennifer. "Reid's Foundation for the Primary/Secondary Quality Distinction." The Philosophical Quarterly 52 (2002): 478494. This issue includes a previously unpublished manuscript by Reid ("Of Power") and ten articles on his philosophy.

O'Connor, Timothy. "Thomas Reid on Free Agency." Journal of the History of Philosophy 32 (1994): 605622.

Rowe, William L. Thomas Reid on Freedom and Morality. Ithaca, NY: Cornell University Press, 1991.

Van Cleve, James. "Thomas Reid's Geometry of Visibles." The Philosophical Review 111 (2002): 373416.

Wolterstorff, Nicholas. Thomas Reid and the Story of Epistemology. Cambridge, U.K.: Cambridge University Press, 2001.

Woudenberg, Rene van, and Terence Cuneo, eds. The Cambridge Companion to Reid. Cambridge, U.K.: Cambridge University Press, 2004.

Yaffe, Gideon. Manifest Activity: Thomas Reid's Theory of Action. Oxford: Clarendon Press, 2004.

For complete bibliographies of Reid's own works and secondary sources, see Reid Studies 1 (1998): 7181; 2 (1998): 5778; and 4 (2000): 9396.

The Center for Scottish Philosophy, based at the University of Aberdeen, maintains the following web site with information about events and publications relating to Reid:

James Van Cleve (2005)

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Reid, Thomas (1710–1796)

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