The causality debate has been centered on two issues, one metaphysical, the other epistemic. The metaphysical issue concerns the nature of the connection between cause and effect: How and in virtue of what does the cause bring about the effect? The epistemic issue concerns the possibility of causal knowledge: How, if at all, can causal knowledge be obtained?
Aristotle (384–322 b.c.e.) claimed a sharp distinction between understanding the fact and understanding the reason why (dioti ; aitia ). Though both types of understanding proceed via deductive syllogism, only the latter is characteristic of science because only the latter is tied to the knowledge of causes. In his Posterior Analytics, Aristotle contrasted the following two instances of deductive syllogism:
- Planets do not twinkle; what does not twinkle is near; therefore, planets are near.
- Planets are near; what is near does not twinkle; therefore, planets do not twinkle.
Syllogism A demonstrates the fact that planets are near but does not explain it because it does not state its causes. On the contrary, syllogism B is explanatory because it gives the reason why planets do not twinkle: because they are near. Explanatory syllogisms like B are formally similar to nonexplanatory syllogisms like A. Both are demonstrative arguments of the form: all Fs are Gs; all Gs are Hs; therefore, all Fs are Hs. The difference between them lies in the "middle term" G. In B, but not in A, the middle term states a cause. As Aristotle said: "The middle term is the cause, and in all cases it is the cause that is being sought" (90a5–10). To ask why F is H is to look for a causal link joining F and H. Aristotle's key observation was that, besides being demonstrative, explanatory arguments should also be asymmetric: the asymmetric relation between causes and effects should be reflected in an explanatory asymmetry between the premises and the conclusion of the explanatory arguments—the premises should explain the conclusion and not the other way around.
Aristotle took scientific knowledge to form a tight deductive-axiomatic system whose axioms are first principles, being "true and primary and immediate, and more known than and prior to and causes of the conclusion" (71b20–25). Being an empiricist, he thought that knowledge of causes has experience as its source. But experience on its own cannot lead, through induction, to the first principles: these are universal and necessary and state the ultimate causes. On pain of either circularity or infinite regress, the first principles cannot be demonstrated either. So, something besides experience and demonstration is necessary for the knowledge of first principles. This is a process of abstraction based on intuition, a process that reveals the essences of things—that is, the properties by virtue of which the thing is what it is. In the example B above, it is of the essence of something's being near that it does not twinkle. In the rich Aristotelian ontology, causes are essential properties of their subjects and necessitate their effects. He thought that the logical necessity by which the conclusion follows from the premises of an explanatory argument mirrors the physical necessity by which causes produce their effects.
In his Physics, Aristotle distinguishes between four types of causes. The material cause is "that out of which a thing comes to be"; the formal cause is "the definition of its essence"; the efficient cause is "the primary source of the change or rest"; and the final cause is "that for the sake of which a thing is done" (194b23–195a3). For instance, the material cause of a statue is its material; its formal cause is its form or shape; its efficient cause is its maker; and its final cause is the purpose for which the statue was made. Aristotle thought that a complete causal explanation has to cite all four causes: the efficient cause is the active agent that puts the form on matter for a purpose.
Most of Aristotle's views were accepted by the Scholastics. Aristotle thought that the chains of efficient causes must stop at some "unmoved movers"—that is, things that are themselves unmoved but produce motion to other things. The Scholastics thought that the only proper efficient cause was God, being the ultimate unmoved mover. Later thinkers revolted against all but efficient causality. Efficient causality, what Aristotle called "the source of motion" (195a10), was taken to be the only type of causality by all those who advocated, in one form or another, the mechanical philosophy: in their hands, efficient causality became tantamount to pushings and pullings. Final causes, in particular, were cast to the winds. Where Aristotle saw goals and purposes in nature, mechanical philosophers either excised purpose from nature (Hobbes, Hume) or placed it firmly in the hands of God (Descartes, Leibniz). The moderns also revolted, to varying degrees, against the rich ontological landscape that Aristotle had painted: essences, substantial forms, activities, and so on. However, two key Aristotelian ideas, that there is necessity in nature and that this necessity is the same as the logical necessity of a demonstrative argument, were to become part of the mainstream philosophical thinking about causality until David Hume (1711–1776) subjected them to severe criticism and undermined them.
René Descartes (1596–1650) distinguished all substances into two sorts: thinking things (res cogitans ) and extended things (res extensa ). He took the essence of mind to be thought and that of matter extension. Unlike Aristotle, he thought that matter was inert (since its essence is that it occupies space). Yet, there are causal connections between bodies (bits of matter) and between minds and bodies (bits of different substances). So, two big questions emerge within Cartesianism. The first is: how is body-body interaction possible? The second is: how is mind-matter interaction possible? Descartes's answer to the first question is the so-called transference model of causality: when x causes y, a property of x is communicated to y. He thought that this view is an obvious consequence of the principle "Nothing comes from nothing." As he put it: "For if we admit that there is something in the effect that was not previously present in the cause, we shall also have to admit that this something was produced by nothing" (vol. 1, p. 97). But Descartes failed to explain how this communication is possible. Indeed, by taking matter to be an inert extended substance, he had to retreat to some external cause of motion and change. Descartes treated forces with suspicion since they did not quite fit within his tight scheme of the two distinct substances and their two essential attributes. So in his Principles of Philosophy (1644) he retreated to God, whom he took to be "the efficient cause of all things" (vol. 1, p. 202). But this retreat to God cannot save the transference model. Besides, the transference model of causality makes an answer to the second question above (how do mind and matter interact?) metaphysically impossible. Being distinct substances, they have nothing in common that can be communicated between them. Descartes was a rationalist. He thought that Reason alone can, by a priori reflection, discover the basic casual laws of nature, which, Descartes thought, stem directly from God.
Descartes's successors were divided into two groups: the occasionalists and those who reintroduced activity into nature. Occasionalism is the view that the only real cause of everything is God and that all causal talk that refers to worldly substances is a sham. Nicolas Malebranche (1638–1715) drew a distinction between real causes and natural causes (or occasions). As he put it: "A true cause as I understand it is one such that the mind perceives a necessary connection between it and its effect. Now the mind perceives a necessary connection between the will of an infinite being and its effect. Therefore, it is only God who is the true cause and who truly has the power to move bodies" (1997, p. 450). Natural causes are then merely the occasions on which God causes something to happen. Malebranche pushed Cartesianism to its extremes: since a body's nature is exhausted by its extension, bodies cannot have the power to move anything, and hence to cause anything to happen. What Malebranche also added was that since causality involves a necessary connection between the cause and the effect (a view that Descartes accepted too), and since no such necessary connection is perceived in cases of alleged worldly causality (where, for instance, it is said that a billiard ball causes another one to move), there is no worldly causality: all there is in the world is regular sequences of events, which strictly speaking are not causal. Gottfried Wilhelm Leibniz (1646–1716), on the other hand, aimed to reintroduce forces and active powers into nature. As he said: "activity is the essence of substance" (1981, p. 65). Each substance is sustained by an internal "primitive active force," which causes its subsequent states. Yet, in a rather puzzling move, he also thought that there is no real causality in nature, since Leibnizian substances (what he called "the monads") do not interact. Rather, they are coordinated with each other by God's act of preestablished harmony, which confers on them the natural agreement of exact clocks.
There is an irony to be noted at this point. Most early modern philosophers tried to solve the metaphysical issue of causality. They devised elaborate theories to explain how the cause brings about the effect. But in the end, they excised causality from nature. More mildly put, insofar as there was causality in nature it was taken to be the product of divine impulse (Descartes) or of mysterious primitive forces (Leibniz).
In his ground-breaking A Treatise of Human Nature (1739–1740), David Hume made the scientific hunt for causes possible, by freeing the concept of causality from the metaphysical chains that his predecessors had used to pin it down. For Hume, causality, as it is in the world, is a regular succession of event-types: one thing invariably following another. His famous first definition of causality runs as follows: "We may define a CAUSE to be 'An object precedent and contiguous to another, and where all the objects resembling the former are plac'd in like relations of precedency and contiguity to those objects, that resemble the latter'" (1978 ed., p. 170).
Taking a cue from Malebranche, Hume argued that there was no perception of the supposed necessary connection between the cause and the effect. When a sequence of events that is considered causal is observed—for example, two billiard balls hitting each other and flying apart—there are impressions of the two balls, of their motions, of their collision, and of their flying apart, but there is no impression of any alleged necessity by which the cause brings about the effect. Hume went one step further. He found worthless his predecessors' appeals to the power of God to cause things to happen, since, as he said, such claims give us "no insight into the nature of this power or connection" (p. 249). So, Hume secularized completely the notion of causality. He also found inadequate, because circular, his predecessors' attempts to explain the link between causes and effects in terms of powers, active forces, and so on. As he put it: "[T]he terms efficacy, agency, power, force, energy, necessity, connexion, and productive quality, are all nearly synonymous; and therefore 'tis an absurdity to employ any of them in defining the rest" (p. 157).
Yet Hume faced a puzzle. According to his empiricist theory of ideas, there are no ideas in the mind unless there were prior impressions (perceptions). He did, however, recognize that the concept of causality involved the idea of necessary connection. Where does this idea come from, if there is no perception of necessity in causal sequences? Hume argued that the source of this idea is the perception of "a new relation betwixt cause and effect": a "constant conjunction" such that "like objects have always been plac'd in like relations of contiguity and succession" (p. 88). The perception of this constant conjunction leads the mind to form a certain habit or custom: to make a "customary transition" from cause to effect. It is this felt determination of the mind that affords us the idea of necessity.
So instead of ascribing the idea of necessity to a feature of the natural world, Hume took it to arise from within the human mind, when the latter is conditioned by the observation of a regularity in nature to form an expectation of the effect, when the cause is present. Indeed, Hume offered a second definition of causality: "A CAUSE is an object precedent and contiguous to another, and so united with it, that the idea of the one determines the mind to form the idea of the other, and the impression of the one to form a more lively idea of the other" (p. 170). Hume thought that he had unpacked the "essence of necessity": it "is something that exists in the mind, not in the objects" (p. 165). He claimed that the supposed objective necessity in nature is spread by the mind onto the world. Hume can be seen as offering an objective theory of causality in the world (since causation amounts to regular succession), which was however accompanied by a mind-dependent view of necessity. This dual aspect of Hume's account of causality is reflected in his two definitions.
Being an empiricist, Hume argued that all causal knowledge stems from experience. He revolted against the traditional view that the necessity that links cause and effect is the same as the logical necessity of a demonstrative argument. He argued that there can be no a priori demonstration of any causal connection, since the cause can be conceived without its effect and conversely. His far-reaching observation was that the alleged necessity of causal connection cannot be proved empirically either. As he famously argued, any attempt to show, based on experience, that a regularity that has held in the past will or must continue to hold in the future will be circular and question-begging. It will presuppose a principle of uniformity of nature. But this principle is not a priori true. Nor can it be proved empirically without circularity. For any attempt to prove it empirically will have to assume what needs to be proved—namely, that since nature has been uniform in the past it will or must continue to be uniform in the future. This Humean challenge to any attempt to establish the necessity of causal connections on empirical grounds has become known as his skepticism about induction. But it should be noted that Hume never doubted that people think and reason inductively. He just took this to be a fundamental psychological fact about human beings that cannot be accommodated within the confines of the traditional conception of Reason. Indeed, Hume went on to describe in detail some basic "rules by which to judge of causes and effects" (p. 173).
It was Hume's critique of necessity in nature that awoke Immanuel Kant (1724–1804) from his "dogmatic slumber," as he himself famously stated. In his Critique of Pure Reason (1787), Kant tried to demonstrate that the principle of causality—namely, "everything that happens, that is, begins to be, presupposes something upon which it follows by rule," (1965 ed., p. 218)—is a precondition for the very possibility of objective experience. He took the principle of causality to be required for the mind to make sense of the temporal irreversibility that there is in certain sequences of impressions. So, whereas we can have the sequence of impressions that correspond to the sides of a house in any order we please, the sequence of impressions that correspond to a ship going downstream cannot be reversed: it exhibits a certain temporal order (or direction). This temporal order by which certain impressions appear can be taken to constitute an objective happening only if the later event is taken to be necessarily determined by the earlier one (i.e., to follow by rule from its cause). For Kant, objective events are not "given": they are constituted by the organizing activity of the mind and in particular by the imposition of the principle of causality on the phenomena. Consequently, the principle of causality is, for Kant, a synthetic a priori principle.
Ingenious though Kant's answer to Hume was, it was ironic in three respects. Firstly, Kant safeguarded the concept of causality but at the price of making it applicable only to the phenomena and not to the unknowable things-in-themselves (noumena). Secondly, recall that Hume argued that the supposed necessity of causal sequences cannot be observed in the sequences themselves, but is projected by the mind onto the world. Kant agreed with all this, but took this projection by the mind onto the world to be presupposed for the distinction between causal and noncausal sequences. Thirdly, Kant identified causality with the rule of natural law: causal sequences of events are lawful sequences of events. This became the main plank of the Humean philosophical tradition. Stripped from objective necessity, natural laws boil down to worldly regularities.
The Regularity View of Causality
Arthur Schopenhauer (1788–1860) charged Kant with showing the absurd result that all sequence is consequence. As he noted, the tones of a musical composition follow each other in a certain objective order and yet it would be absurd to say that they follow each other according to the law of causality. This has also been a major objection to Hume's views. Hume left the metaphysics of causality behind, but like Kant, he ended up with a loose notion of causality. On the one hand, it seems that there can be causality without regularity. This is the case of the so-called singular causality, where one event causes another to happen without this particular (singular) sequence of events falling under a regularity. On the other hand, there can be regularity without causality. There are cases in which events regularly follow each other (like the night always follows the day) without being the cause of each other. Once more, the metaphysical and the epistemological issues of causality come to the fore. We might not be able to know that a sequence of events is causal unless we see it repeat itself many times. But this does not imply that, metaphysically speaking, causality consists in regular sequence. On the Humean view, whether or not a sequence of events is causal depends on things that happen elsewhere and elsewhen in the universe, and in particular on whether or not this particular sequence instantiates a regularity. The Humean view may be entitled the Regularity View of Causality. But an opposite view that became prominent in the twentieth century, due mostly to the work of Curt John Ducasse (1881–1969), is that what makes a sequence of events causal is something that happens there and then: a local tie between the cause and the effect, or an intrinsic feature of the particular sequence. Ducasse's (1968) single-difference account, roughly that an event c causes an event e if and only if c was the last—or, the only—difference in e 's environment before e occurred, takes causality to link individual events independently of any regular association that there may or may not be between events like the cause and events like the effect. Causality, non-Humeans argue, is essentially singular: a matter of this causing that.
Most advocates of singular causation argue that, contra Hume, causality is observable. A central claim is that causal relations are embodied in language by causal verbs, such as "to bend," "to corrode," "to push," "to break," and so on. So, we are told, when one asserts that, for instance, the vase broke after being struck with a hammer, by the very use of the verb "to break," one makes a causal claim, and one has thereby directly perceived the vase being caused to break. Elizabeth Anscombe (b. 1919) argued that since our language is infested with causal verbs, there is no mystery in the claim that we directly perceive causings: when we learn to report such things as pushings, pullings, breakings, and the like from having observed them, we have thereby learned to report causings from having observed them.
In his monumental A System of Logic Ratiocinative and Inductive (1843), John Stuart Mill (1806–1873) defended the Regularity View of Causality, with the sophisticated addition that in claiming that an effect invariably follows from the cause, the cause should be taken to be the whole conjunction of the conditions that are sufficient and necessary for the effect. For Mill, regular association is not, on its own, enough for causality. A regular association of events is causal only if it is "unconditional"—that is, only if its occurrence does not depend on the presence of further factors which are such that, given their presence, the effect would occur even if its putative cause was not present. A clear case in which unconditionality fails is when the events that are invariably conjoined are effects of a common cause. Ultimately, Mill took to be causal those invariable successions that constitute laws of nature.
Mill is also famous for his methods by which causes can be discovered. These are known as the Method of Agreement and the Method of Difference. According to the first, the cause is the common factor in a number of otherwise different cases in which the effect occurs. According to the second, the cause is the factor that is different in two cases, which are similar except that in the one the effect occurs, while in the other it does not. In effect, Mill's methods encapsulate what is going on in controlled experiments: we find causes by creating circumstances in which the presence (or the absence) of a factor makes the only difference to the production (or the absence) of an effect. Mill, however, was adamant that his methods work only if certain metaphysical assumptions are in place. It must be the case that: (a) events have causes; (b) events have a limited number of possible causes; and (c) same causes have same effects, and conversely.
Bertrand Russell (1872–1970), in his "On the Notion of Cause" (1918), argued that the concept of causality was incoherent. But this was just as well for him, since, as he claimed, physics has stopped looking for causes: for "there are no such things." Here is his famous dictum: "The law of causality, I believe, like much that passes muster among philosophers, is a relic of a bygone age, surviving, like the monarchy, only because it is erroneously supposed to do no harm" (1918, p. 180). His suspicion of the concept of causality was inherited by the movement of logical positivism (the Vienna Circle), which set the agenda for most of the philosophy of science in the twentieth century. They took to heart Hume's critique of the supposed necessary connection between cause and effect. The twist they gave to this critique was based on their verificationist criterion of meaning. As the leader of the Circle, Moritz Schlick (1882–1936), stressed, positing a "linkage" between two events would be tantamount to "committing a kind of nonsense" since all attempts to verify it would be necessarily futile (1979, p. 245). Rudolf Carnap (1891–1970) thought that insofar as the concept of causality is useful to science, it should be understood by reference to the notion of laws of nature. He insisted that the only meaningful content that causal talk can have is when we call "cause" the event, or the physical magnitude, or the physical state, which temporally precedes another one nomologically dependent on the former. The logical positivists took the laws to be exceptionless regularities that are expressed by true universal statements of the form "all Fs are Gs" (e.g., all planets move in ellipses).
A central element of the empiricist project was to legitimize—and demystify—the concept of causality by subsuming it under the concept of lawful explanation, which, in turn, was modeled on deductive arguments. This project culminated in Carl Hempel (1905–1977) and Paul Oppenheim's Deductive-Nomological model of explanation. According to this, to offer an explanation of an event e is to construct a valid deductive argument of the following form:
Statements of Laws
Therefore, e (event/fact to be explained)
So, when the claim is made that event c causes event e (e.g., that the sugar cube dissolved because it was immersed in water), it should be understood as follows: there are relevant laws in virtue of which the occurrence of the antecedent condition c (putting the sugar in water) is nomologically sufficient for the occurrence of the event e (the dissolving of the sugar). It has been a standard criticism of the Deductive-Nomological (DN) model that, insofar as it aims to offer sufficient and necessary conditions for an argument to count as a bona fide explanation, it fails. For, there are arguments that satisfy the structure of the DN-model, and yet fail to be bona fide explanations of a certain event. For instance, one can construct a deductive-nomological "explanation" of the height of a flagpole having as premises (a statement of) the length of its shadow and (statements of) relevant laws of optics, but this is not an explanation of why the flagpole has the height it does. In a sense, this counterexample repeats a point that we saw already made by Aristotle—namely, that good explanations are asymmetric: they explain effects in terms of causes and not conversely. Conversely, there are bona fide explanations that fail to instantiate the DN-model. For instance, one can construct an explanation of why there was a car crash (by telling a causal story of how it happened) without referring to any law at all. The joined message of these counterexamples is that the DN-model fails precisely because it ignores the role of causality in explanation. In other words, the moral of the counterexamples is there is more to the concept of causality than what can be captured by DN-explanations.
Laws of Nature
Be that as it may, the Deductive-Nomological model, as well as any attempt to tie causality to laws, faces a rather central conceptual difficulty: the problem of how to characterize the laws of nature. Most Humeans have come to adopt the Regularity View of Laws: laws of nature are regularities. Yet, they have a hurdle to jump: not all regularities are causal. Nor can all regularities be deemed laws of nature. The night always follows the day, but it is not caused by the day. And, though a regularity, it is not a law of nature that all coins in my pocket are euros. So, the Humeans have to draw a distinction between the good regularities (those that constitute the laws of nature) and the bad ones—that is, those that are, as Mill put it, "conjunctions in some sense accidental." Only the former can underpin causality and play a role in explanation. Among the many attempts to distinguish between laws and accidents, the most promising is what may be called the web of laws view. According to this, the regularities that constitute the laws of nature are those that are expressed by the axioms and theorems of an ideal deductive system of our knowledge of the world, which strikes the best balance between simplicity and strength. Whatever regularity is not part of this best system is merely accidental: it fails to be a genuine law of nature. The gist of this approach, which has been advocated by Mill, Frank Ramsey (1903–1930), and David Lewis (1941–2001), is that no regularity, taken in isolation, can be deemed a law of nature. The regularities that constitute laws of nature are determined in a kind of holistic fashion by being parts of a structure. But despite its many attractions, this view does not offer a purely objective account of laws of nature.
A contrary view that has been defended by David Armstrong (b. 1926) is that lawhood cannot be reduced to regularity. Lawhood is said to be a certain necessitating relation among natural properties. An attraction of this view is that it makes clear how laws can cause anything to happen: they do so because they embody causal relations among properties. But the central concept of nomic necessitation is still not sufficiently clear.
There are some philosophers who assert that secondary causes act through their matter, figure, and motion … others assert that they do so through a substantial form; others through accidents or qualities, and some through matter and form; of these some through form and accidents, others through certain virtues or faculties different from the above.… Philosophers do not even agree about the action by which secondary causes produce their effects. Some of them claim that causality must not be produced, for it is what produces. Others would have them truly act through their action; but they find such great difficulty in explaining precisely what this action is, and there are so many different views on the matter that I cannot bring myself to relate to them.
source: Nicolas Malebranche, The Search After Truth (Researche de la Vérité ) (1674–1675), trans. Thomas M. Lennon and Paul J. Olscamp. Cambridge, U.K., and New York: Cambridge University Press, 1997, p. 659.
Among the more recent attempts to develop more defensible versions of the Regularity View of Causality, J. L. Mackie's (1917–1981) inus-conditions approach stands out. Mackie stressed that effects have, typically, a "plurality of causes" (p. 61). That is, a certain effect can be brought about by a number of distinct clusters of factors. Each cluster is sufficient to bring about the effect, but none of them is necessary. So, he takes the regularities in nature to have a complex form (A&B&C or D&E&F or G&H&I) ↔ E, which should be read as: all (A&B&C or D&E&F or G&H&I) are followed by E, and all E are preceded by (A&B&C or D&E&F or G&H&I). How do we pick out the cause of an event in this setting? Each single factor of A&B&C (e.g., A) is related to the effect E in an important way. It is an insufficient but nonredundant part of an unnecessary but sufficient condition for E. Using the first letters of the italicized words, Mackie has called such a factor an inus condition. Causes, then, are inus conditions. So to say that short circuits cause house fires is to say that the short circuit is an inus condition for house fires. It is an insufficient part because it cannot cause the fire on its own (other conditions such as oxygen, inflammable material, etc. should be present). It is, nonetheless, a nonredundant part because, without it, the rest of the conditions are not sufficient for the fire. It is just a part, and not the whole, of a sufficient condition (which includes oxygen, the presence of inflammable material, etc.), but this whole sufficient condition is not necessary, since some other cluster of conditions, for example, an arsonist with gasoline, can produce the fire.
In his Enquiry Concerning Human Understanding (1748) Hume stated briefly another way to view causality. He said that an object is the cause of another when "if the first object had not been, the second never had existed" (1975 ed., p. 146). This view has been articulated into a theory of causality by David Lewis. Lewis (1986) defined causality in terms of the counterfactual dependence of the effect on the cause: the cause is rendered counterfactually necessary for the effect. For instance, to say that the short-circuit caused the fire is to say that if the short-circuit had not happened, the fire would not have ensued. To be more precise, Lewis defined causality by reference to a causal chain of counterfactually dependent events, where a sequence of events (C, E, E, …) is a chain of counterfactual dependence if and only if E counterfactually depends on C, E counterfactually depends on E, and so on. This move is meant to enforce that causation is a transitive relation among events (that is, if C causes E and E causes E, then C causes E ). As Lewis put it: "one event is a cause of another if and only if there exists a causal chain leading from the first to second" (p. 167). Statements such as "if C had happened, then E would have happened" are called counterfactual conditionals (another example, "if this sugar cube had been in water, it would have dissolved") for they state what could or could not have happened, under certain circumstances. But it has been notoriously difficult to specify the conditions under which counterfactual conditionals are true or false. Lewis articulated a rather complicated logic of counterfactual conditionals, which was based on the idea that, besides the actual world, there are also other possible worlds, which can be deemed more or less similar to the actual. A chief but not inviolable criterion for judging the similarity among worlds was taken to be whether the same laws of nature govern the worlds under comparison.
Though it is still one of the main contestants, this view of causality faces important difficulties. A chief among them comes from cases of causal overdetermination, where there are two factors each of which is sufficient to bring about the effect, but none of them is necessary, since even if the one was not present, the other factor would ensure the occurrence of the effect. For instance, two rocks are simultaneously thrown at a bottle and they shatter it. They both caused the shattering, but the effect is not counterfactually dependent on either of them, since if the first rock had missed the bottle, the other would have still shattered it. So there is causality without the cause being counterfactually dependent on the effect.
Here is a billiard-ball lying on the table, and another ball moving towards it with rapidity. They strike; and the ball, which was formerly at rest, now acquires a motion. This is as perfect an instance of the relation of cause and effect as any which we know, either by sensation or by reflection. Let us therefore examine it. 'Tis evident, that the two balls touched one another before the motion was communicated, and that there was no interval betwixt the shock and the motion. Contiguity in time and place is therefore a requisite circumstance to the operation of all causes. 'Tis evident likewise, that the motion, which was the cause, is prior to the motion, which was the effect. Priority in time, is therefore another requisite circumstance in every cause. But this is not all. Let us try any other balls of the same kind in a like situation, and we shall always find, that the impulse of the one produces motion in the other. Here therefore is a third circumstance, viz., that is a constant conjunction betwixt the cause and effect. Every object like the cause, produces always some object like the effect. Beyond these three circumstances of contiguity, priority, and constant conjunction, I can discover nothing in this cause. The first ball is in motion; touches the second; immediately the second is in motion: and when I try the experiment with the same or like balls, in the same or like circumstances, I find that upon the motion and touch of the one ball, motion always follows in the other. In whatever shape I turn this matter, and however I examine it, I can find nothing farther.(pp. 649–650)
source: David Hume, Abstract to A Treatise of Human Nature. Published by Hume anonymously in 1739.
No matter how one thinks about causality, there are certain platitudes that this concept should satisfy. One of them may be called the difference platitude: causes make a difference—namely, things would be different if the causes of some effects were absent. This platitude is normally cast in two ways. We have already seen the first, the counterfactual way: if the cause had not been, the effect would not have been either. The other is a probabilistic way: causes raise the chances of their effects—namely, the probability that a certain event happens is higher if we take into account its cause than if we do not. This thought has led to the development of theories of probabilistic causality. We do rightly claim that smoking causes lung cancer, even though there is no regular association (or deterministic connection) between smoking and lung cancer. Some philosophers, most notably Patrick Suppes (1984) and Nancy Cartwright (1983), think that this is already a good argument against the view that causality is connected with invariable sequences or regularities. They then analyze causal claims in terms of probabilistic relations among magnitudes, capitalizing on the intuition that causes (mostly, but not invariably) raise the probabilities of their effects. Some think that there are good empirical reasons to jettison determinism (roughly, that each and every event has a fully sufficient set of causes) in favor of indeterminism (roughly, that there are genuinely chancy events). They then try to show that indeterminism and causality mix well, given the thought that a certain event can be caused to happen even though its cause made only a difference to its chance to happen. Interestingly, these ideas are extended to deterministic causality as well, with the prime thought being that an effect is deterministically caused to happen if its probability, given its cause, is unity.
Causes as Recipes
Another central platitude of the concept of causality may be called the recipe platitude: causes are recipes for producing or preventing their effects. This platitude is normally cast in terms of manipulability: causes can be manipulated to bring about certain effects. G. H. von Wright (1906–2003) developed this thought into a full-blown theory of causality. He took it that what confers on a sequence of events the character of causal connection is "the possibility of subjecting cause-factors to experimental test by interfering with the 'natural' course of events" (1993, p. 117). Since manipulation is a distinctively human action, he concluded that the causal relation is dependent upon the concept of human action. But his views were taken to be too anthropomorphic. For, do we not think that there would be causal relations, even if there would not be any humans around capable of manipulating anything? Yet, recently, there have been important attempts to give a more objective gloss to the idea of manipulation. James Woodward (2003) introduces a notion of intervention that is not restricted to human action and argues that a relationship among some magnitudes X and Y is causal if, were one to intervene to change the value of X appropriately, the relationship between X and Y would remain invariant but the value of Y would change, as a result of the intervention on X. This interventionist account has been developed by Judea Pearl (2001) into a rather powerful mathematical tool, known as Bayesian probabilistic networks, for discovering and establishing causal relations from relations of probabilistic dependence among variables. An attraction of the interventionist approach is that it is not so much concerned with the metaphysics of causality as with the epistemological and methodological circumstances under which causal facts can be ascertained.
Lately, there have been a number of attempts to show that there is more to causality than regular succession by positing a physical mechanism that links cause and effect. In his Scientific Explanation and the Causal Structure of the World (1984), Wesley Salmon (1925–2001) advanced a mechanistic approach, roughly that an event c causes an event e if and only if there is a causal process that connects c and e. Borrowing an idea of Hans Reichenbach's (1956), Salmon characterized "causal" those processes that are capable of transmitting a mark, where a mark is a modification of the structure of a process. Later on, Salmon (1997) and Phil Dowe (2000) took causality to consist in the exchange or transfer of some conserved quantity, such as energy-momentum or charge. Such accounts may be called transference models because they claim that causality consists in the transfer of something (some physical quantity) between the cause and its effect. They claim that causality need not involve regularities or laws. Rather, it consists in a local physical tie between cause and effect. But there is a drawback. Even if it is granted that these models offer neat accounts of causality at the level of physical events or processes, they can be generalized as accounts of causality simpliciter only if they are married to strong reductionistic views that all worldly phenomena (be they social or psychological or biological) are, ultimately, reducible to physical phenomena. We saw earlier that Descartes, too, advanced a transference model of causality and that he stumbled on the issue of mental causality: how can the mental cause anything physical to happen, as it manifestly does? The irony is that the very same hurdle might have to be jumped by the advocates of the modern transference models.
[W]e derived the principle that everything that happens has a cause from the condition under which alone a concept of happening in general is objectively possible—namely, by showing that the determination of an event in time, and therefore the event as belonging to experience, would be impossible save as standing under such a dynamical rule.
Hume found any appeal to causal powers suspect, since he thought there were no impressions of them. Hume's views were dominant until the last quarter of the twentieth century, when there was a resurgence of Aristotelianism. A few contemporary philosophers think that causation should be best understood in terms of causal powers—that is, powers, dispositions, and capacities things have to cause other things to happen. These powers are supposed to stem from the nature or essence of a thing and they determine what a thing is and what it can do. The causal laws that govern the world are supposed to stem from these causal powers. According to Brian Ellis (2001), a chief defender of this view, causal laws state necessary truths about how things are intrinsically disposed to behave. But many philosophers find these views unappealing, not least because they fail to explain the fundamental notion of causal power.
See also Aristotelianism ; Cartesianism ; Determinism ; Dualism ; Empiricism ; Neoplatonism ; Probability .
Anscombe, G. E. M. Causality and Determination. London: Cambridge University Press, 1971.
Aristotle. Physics. In vol. 1 of The Complete Works of Aristotle, 2 vols., edited by Jonathan Barnes. Princeton N.J.: Princeton University Press, 1984.
——. Posterior Analytics. 2nd ed. Translated by Jonathan Barnes. Oxford: Clarendon, 1993.
Armstrong, D. M. What Is a Law of Nature? Cambridge, U.K., and New York: Cambridge University Press, 1983. Classic defense of the view that natural laws embody necessitating relations among properties.
Carnap, Rudolf. An Introduction to the Philosophy of Science. Edited by Martin Gardner. New York: Dover, 1995. A classic late statement of the positivist philosophy of science.
Cartwright, Nancy. How the Laws of Physics Lie. Oxford and New York: Clarendon, 1983. A thorough critique of the Regularity Views of Causation and Laws.
Descartes, René. The Philosophical Writings of Descartes. 3 vols. Translated by John Cottingham, Robert Stoothoff, and Dugald Murdoch. Cambridge, U.K., and New York: Cambridge University Press, 1985. Vol. 1 includes Principles of Philosophy (1644), Descartes's classic presentation of his philosophy of nature.
Dowe, Phil. Physical Causation. Cambridge, U.K., and New York: Cambridge University Press, 2000. The standard rendition of the conserved-quantity theory of causation.
Ducasse, C. J. Causation and the Types of Necessity. New York: Dover, 1969. Defends singular causation against Hume and Mill.
Ellis, B. D. Scientific Essentialism. Cambridge, U.K., and New York: Cambridge University Press, 2001. A thorough defense of neo-Aristotelianism.
Hempel, Carl G. Aspects of Scientific Explanation, and Other Essays in the Philosophy of Science. New York: Free Press, s1965.
Hume, David. An Enquiry Concerning Human Understanding (1748). Edited by L. A. Selby-Bigge from the posthumous edition of 1777. 3rd ed., edited by P. H. Nidditch, published as Enquiries Concerning Human Understanding and Concerning the Principles of Morals. Oxford: Clarendon, 1975. A less skeptical version of Hume's critique of causality.
——. A Treatise of Human Nature. 1739. Edited by L. A. Selby-Bigge, 1888. 2nd ed., with text revisions by P. H. Nidditch. Oxford: Clarendon, 1978.
Kant, Immanuel. Critique of Pure Reason. 1787. Translated by Norman Kemp Smith. New York: St. Martin's Press, 1965. A classic of Western philosophy.
Leibniz, Gottfried Wilhelm. New Essays on Human Understanding. 1765. Translated and edited by Peter Remnant and Jonathan Bennett. Cambridge, U.K., and New York: Cambridge University Press, 1981. Posthumously published defense of rationalism against John Locke's empiricism.
Lewis, David. "Causation." In his Philosophical Papers, vol. 2. Oxford: Oxford University Press, 1986.
Mackie, J. L. The Cement of the Universe: A Study of Causation. Oxford: Clarendon, 1974. One of the most comprehensive and original books on causality.
Malebranche, Nicolas. The Search After Truth (1674–1675). Translated by Thomas M. Lennon and Paul J. Olscamp. Cambridge, U.K., and New York: Cambridge University Press, 1997.
Mill, J. S. A System of Logic: Ratiocinative and Inductive (1843). 8th ed. London: Longmans, Green and Co., 1911. Wideranging treatment of the methodology of science.
Pearl, Judea. Causality: Models, Reasoning, and Inference. Cambridge, U.K.: Cambridge University Press, 2001. Technical but insightful.
Ramsey, F. P. "Universals of Law and of Fact." 1928. In Foundations: Essays in Philosophy, Logic, Mathematics and Economic, edited by D. H. Mellor. London: Routledge and Kegan Paul, 1978.
Reichenbach, Hans. The Direction of Time. Edited by Maria Reichenbach. Berkeley and Los Angeles: University of California Press, 1956. A defense of the view that the direction of time stems from the direction of causation.
Russell, Bertrand. "On the Notion of Cause." In his Mysticism and Logic, and Other Essays. London: George Allen and Unwin, 1932. First published in 1918.
Salmon, Wesley. Causality and Explanation. New York: Oxford University Press, 1998.
——. Scientific Explanation and the Causal Structure of the World. Princeton, N.J.: Princeton University Press, 1984. The most systematic contemporary mechanistic account of causality.
Schlick, Moritz. "Causation in Everyday Life and in Recent Science." 1932. In Moritz Schlick Philosophical Papers, Vol. 2 (1925–1936). Edited by Henk L. Mudler and Barbara F. B. De Velde-Schlick. Dordrecht, Netherlands: D. Reidel, 1979.
Suppes, Patrick. Probabilistic Metaphysics. Oxford: Blackwell, 1984.
von Wright, G. H. "On the Logic of the Causal Relations." In Causation, edited by Ernst Sosa and Michael Tooley. Oxford: Oxford University Press, 1993.
Woodward, James. Making Things Happen: A Theory of Causal Explanation. New York: Oxford University Press, 2003. The standard development of the interventionist approach.
Clatterbaugh, Kenneth. The Causation Debate in Modern Philosophy, 1637–1739. New York: Routledge, 1999. Excellent survey of the main theories of causality from Descartes to Hume.
Eells, Ellery. Probabilistic Causality. Cambridge, U.K.: Cambridge University Press, 1991. A thorough treatment of theories of probabilistic causality.
Sosa, Ernest, and Michael Tooley, eds. Causation. Oxford: Oxford University Press, 1993. A collection of the most influential philosophical papers on causation in the second half of the twentieth century.
Stroud, Barry. Hume. London: Routledge and Kegan Paul, 1977. Still the best presentation of Hume's philosophy.
In a general sense causality designates anything that has the character of a cause; more specifically it describes the relationship between cause and effect. Sometimes it is distinguished from causation, which is taken to mean any type of causative action (see action and passion). Cause (Gr. αἰτια, αἵτιον; Lat. causa ) is itself defined by scholastics as, that from which something else proceeds with a dependence in being. It is related to principle, which is that from which something proceeds in any way whatsoever; to condition, which is a prerequisite factor needed to make causal action effective; and to occasion, which is an opportunity that may induce a free agent to act.
This article first exposes Greek and scholastic teaching on causality, furnishing a brief historical survey of its development to medieval times, together with an analysis of the nature of causality and the corollaries it entails. It then recounts and criticizes views on causality held by some of the principal philosophers of the modern and contemporary periods.
Greek and Scholastic Teaching
The origins of causality in Greek thought are summarized in various works of aristotle (esp. Meta. 983a 25–984b 20). Aristotle notes that while none of the previous philosophers had furnished a systematic exposition of causality, their separate and sometimes confused treatments give evidence of four different types of causes.
CLASSIFICATION AND HISTORY
The four causes enumerated by Aristotle are "the matter, the form, the mover, and 'that for the sake of which'" (Phys. 198a 20–25). These have became known as the material, formal, efficient and final causes.
Basic definitions. By matter or material cause Aristotle means "that out of which a thing comes to be and which persists." Examples would be the cloth out of which a suit is made and the tobacco of a cigar. By form or formal cause he refers to "the form or archetype, that is, the statement of the essence." In art, the shape of a bowl would constitute its formal cause; in nature, the soul of a living thing would be its formal cause. By mover, agent, or efficient cause Aristotle understands the "primary source of the change or coming to rest" (see efficient causality). Thus a carpenter is the efficient cause of a house's being built, or wind is the cause of the motion of waves on water. By final cause, he means that "in the sense of end or that for the sake of which a thing is done" (see final causality). For example, one studies in order to become learned, or the natural camouflage of animals is for the sake of protecting them from their enemies. Final cause may also refer to the object of desire or the desire of the object. (Confer, Phys. 194b 20–35.)
Pre-Socratics. The earliest of the causes, sought by the pre-Socratics although not formally recognized as such, was the material cause. All the Ionians searched for one or more types of matter composing the cosmos, some opting for water (Thales), others for air (Anaximenes) or an indeterminate apeiron (Anaximander). Later philosophers enquired into the material and the efficient causes of things. empedocles, for example, posited friendship and strife as the forces uniting or dissolving the combination of the elements, thus accounting for order and chaos respectively. Such forces can be interpreted along the lines of efficient causality. anaxagoras also apparently hinted at efficient causality in his doctrine of Nous, although, as Aristotle observed, this offered more promise that it gave (see greek philosophy).
Socrates and Plato. socrates may be said to have searched for the final causes of human conduct in his quest for the virtuous life. The Pythagoreans and especially plato, made further advance into the quest for causes by investigating formal causality. For Plato, these forms or archetypes in the world of ideas are the patterns participated and imitated by sensible reality. Analogously, as a shadow has its meager reality from the tree that casts it and the sun that makes this possible, so the sensory world has its reality by virtue of the ideas (forms) it imitates and the One above the ideas. This theme of participation runs throughout many of Plato's middle and later works. Plato also makes use of efficient causality when he speaks of the demiurge (confer, Timaeus ) as forming the world below.
Aristotelian and other usage. Aristotle not only presented a thorough enumeration and description of the various causes, but went on to employ them extensively in his works. He viewed all science (scientia) as a search for causes, for only causal knowledge is scientific knowledge. His theory of proof or demonstration (confer, Posterior Analytics ) is rooted in this doctrine of causes. The connecting link between a subject (S -term) and its attribute (P -term) is a cause (M -term). Thus the cause (M -term) always tells why P belongs to S or how one knows that P belongs to S. Hence, all science is "a search for the middle term." Both in the Physics and in the Metaphysics, Aristotle comes to the conclusion of the existence of an Unmoved Mover or an Uncaused Cause. The Uncaused Cause is commonly viewed as an object of desire and thus as a final cause, while the Unmoved Mover is often interpreted as an efficient cause. To sum up the importance of Aristotle's contribution on the subject of causality, this lay in his showing to others what to look for when seeking scientific knowledge and how to proceed in such investigation. His systematic treatment and delineation of the causes changed the search for truth from a random groping to a systematic enquiry.
Later Greek thought. After Aristotle, there was comparatively little stress on formal recognition and use of causes. Skeptics rejected them and the Stoics were primarily interested in the ethical life of virtue amidst a pantheistic setting. The latter did, however, stress the immanent causality of the logos in the world and of "seeds" in things as active forms from which reality emerges. The Epicureans accepted atomism with its consequent denial of teleology or final causality. Neoplatonists were principally noted for their attempt to merge Aristotelian and Platonic teachings on causality. They gave further impetus to recognition of a fifth cause, the exemplary cause (see exemplary causality).
Scholastic development. Although Aristotle laid the essential groundwork for the doctrine of causality, it was mainly the scholastics who further clarified, refined and applied his doctrine. Nearly all employed the Aristotelian terms, but many offered various interpretations and applications of the doctrine.
Since the most notable Aristotelian in the medieval Latin West was St. thomas aquinas, his views will be summarized here. St. Thomas defines cause in a number of ways, but two of his definitions contain the essential elements. A cause is "that upon which something else follows of necessity" (In 5 meta. 1.749). Again, a cause is that which "brings some influence on the being of the thing caused" (ibid. 751). The key to understanding causality, for Aquinas, is to see that it always involves a positive principle exerting some influence on a perfection or thing that is coming to be, that is, an influx into being. His definitions are necessarily obscure, for the notion of causality is fundamentally analogical and no analogical term admits of a strict definition (see analogy). One error of present-day thinkers in appraising causality is to ignore this analogical character of the causes and attempt to reduce all causality to some type of efficient cause. This preoccupation leads automatically to mechanism.
JUSTIFICATION OF CAUSALITY
Virtually no philosopher has denied the practical utility and necessity of the concept of causality, although frequent efforts have been directed toward showing that, in the real order, this concept is speculatively unverifiable. Yet man can and does regularly verify the extramental existence of causal influences. His starting point, most evident in experience, is the fact of change. He observes change in nature and experiences himself as capable of producing it. Explanation of the obvious fact of change and motion thus leads to explicit knowledge of the doctrine of causes.
In the most commonplace examples of change, for example, the sculpting of a statue, an agent (efficient cause) does something to a marble subject (material cause). As a result of the agent's activity, the marble comes to possess actually a new shape or determination (formal cause). What prompted this action on the part of the agent was the fact that he sought to produce something: he had some goal at which he aimed (final cause). Briefly, then, in changes produced by art, one observes that there must be a substratum (material cause), a determination (formal cause) that comes to be actually present in the substratum through the activity of an agent (efficient cause), for some purpose (final cause).
Making an analogous transition from art to the order of nature, one sees that the material cause accounts for the continuity that is evident in all changes in the universe; the formal cause is the principle of novelty, without which no change would be manifest; the efficient cause initiates and makes this novelty to come about actually; and the final cause accounts for the action's tending to a determinate effect. The principles involved in this explanation apply then, not merely to art, but to nature and to physical change as such. Consequently and in analogous fashion, one can understand that such causes are also required for any change in the physical world, whether these be substantial or accidental.
St. Thomas summarizes this line of reasoning as follows:
There must of necessity be four causes: because when a cause exists, upon which the being of another thing follows, the being of that which has the cause may be considered in two ways. First, absolutely; and in this way the cause of being is a form by which something is a being-in-act …. It follows of necessity that there are two other causes, namely the matter and the agent that reduces the matter from potency to act. But the action of an agent tends to something determinate, just as it proceeds from some determinate principle, for every agent does what is in conformity with its nature. That to which the action of the agent tends is called the final cause. Thus, there are necessarily four causes. [In 2 phys. 10.15.]
Since change is an objective occurrence in the real order, the principles without which it would be unintelligible are clearly objective as well; hence the foregoing explanation is not to be construed as psychological, but as ontological in character. It requires, moreover, an intellectual insight into the nature of real beings and their operations. Hence, nominalists and empiricists, denying the intellect's ability to grasp natures, also reject this explanation. The exposition above is predicated on the indemonstrable first principle that being is intelligible and accordingly, that man can know (in the sense of understand) reality itself (see first principles).
ANALYSIS OF CAUSALITY
Because the rejection of scholastic views on causality by modern philosophers is based largely on a misunderstanding of what is meant by causality and how it occurs, some refinements of the explanation already given are now attempted.
One or more effects. In a certain sense, the effect of the various causes is but one effect of all four—each contributing to this effect in its own special manner. Yet the following distinctions obtain. Material and formal causes may be regarded as intrinsic, for they enter into the composition of the thing. Efficient and final causes are said to be extrinsic. The material cause influences the being of the effect through its role as subject, recipient and passive principle, thereby limiting the act that it receives. The formal cause has for its effect the determination or specification of the being of the effect, thereby making it to be this kind of thing rather than that. The efficient cause has for its effect the coming-to-be of the new determination (form) in the subject. Lastly, the final cause has for its effect the perfection itself that has come to be, formally considered as a term of the intention of the agent. It should be noted that this intention need not be conscious or cognitive in the agent; it can be simply a tendency of the agent.
Reciprocity of causes. Reciprocity is often evident between causes. The final cause explains why the agent causes, while the agent makes the final cause or end come to be. When the final cause is considered in the order of intention, it is what moves the agent to act. When it is considered in the order of execution, it is what the agent has produced. Thus, as Aristotle observes, health is the final cause of walking, but walking in turn produces or contributes to health. Hence, the final cause may be termed first in the order of intention and last in the order of execution. It is also termed the highest of the causes for without it none of the other causes could actually cause.
Nature of causal action. No agent loses anything in causing. To cause is itself a perfection; for an agent to necessarily lose in causing would be for it to become increasingly less perfect and this implies a contradiction. It must be noted, therefore, that there is no transfer in causing as such—a position St. Thomas calls ridiculum (C. gent. 3.69)—as though the agent causes by "giving up" its own form or perfection, thereby entailing its loss. Leibniz apparently misunderstood the scholastic doctrine in this manner.
Instead, causing by finite beings involves an eduction of the form from the potency of the matter (see matter and form). Strictly, the form does not come from the agent. Rather, by means of the action of the agent, the form that was already potentially in the matter comes to be present there actually. Thus water in becoming warm does not literally receive heat from the fire. It is because the flame is actually hot that water, which is potentially hot, comes to be actually so.
It is nonetheless true to say that finite causes lose in causing, although this is not because they are causing as such. Their loss is due to the presence of other causes acting reciprocally upon them. Since in the physical order every action involves a reaction, it is impossible to separate physically the activity of an agent from its being acted upon by a reciprocal agent. A physical agent, when acting, is always a patient with respect to something else. What is required to understand causality, therefore, is an intellectual abstraction whereby one considers separately two distinct but inseparable elements as these occur in the physical order.
Priority of nature. The priority of the cause to the effect, considering both in the order of act, is not a priority of time but one of nature. The effect flows from the cause and not conversely. Although parents, as human beings, exist temporally before their offspring, they do not do so strictly qua parents. They become parents only at the moment of conception. In the order of act, therefore, a cause and its proper effect are simultaneous. For this reason the effect continues to be only so long as its cause(s) continue to act. It is important to distinguish, therefore, the proper effect of a cause from its general effect. One can say that a tailor is the cause of the suit, as his general effect, but not that the suit is the proper effect of the tailor, for obviously the suit can continue to be when the tailor has died. Rather the proper effect of the tailor is the suit in its coming-to-be. Thus, the suit begins to become, continues becoming and ceases to become only so long as the tailor begins, continues and stops working on it. The suit continues to be, therefore, not because of the tailor—who no longer exerts causal influence with respect to it—but because its material and formal causes effect this conjointly.
Action and passion. With respect to efficient causality, there is only one motion or action, but this gives rise to two categories of being: passion, from the viewpoint of the patient; and action, from the viewpoint of the agent. There is then but one actuation and the change as such is in the patient, not in the agent. This can be more easily stated by saying that the effect is a prolongation of the act of the agent in the patient. There are not two separate acts that somehow must be connected by a third, essentially the mistaken view of Hume; there is but a single act.
Causes of being and becoming. The distinction between a cause in the order of becoming (in fieri ) and a cause in the order of being (in esse ) must also be noted. A creature's causality is limited to the order of becoming, while only God can cause in the order of being. The limitation of a creature's causality is shown by the fact that existence (esse ) proceeds from the form and no creature is a total cause of any form. Rather, creatures are causes of a form's eduction from the potentiality of matter. If creatures do not cause the form as such, much less are they causes of the esse resulting from the form. God's unique causality in the order of being is also clear from the fact that only what is esse can cause it. Since creatures merely have esse, they cannot cause it in the strict sense.
From these notions a number of corollaries follow. One is that nothing can escape the universal causality of God. Since becoming proceeds from being as its principle and tends toward being as its term, becoming always presupposes causality in the order of being. Another corollary is that the causality of any creature presupposes the concurrent causality of God (see concurrence, divine). This should not be viewed as prohibiting genuine secondary causality by creatures, as proposed by occasionalism. Rather it is the very thing that makes creatures capable of exercising their own causality (see causality, divine).
Subdivisions of causes. Among the many distinctions that can be employed to render causality intelligible are those that subdivide the various causes. Thus, material cause may refer to primary matter or secondary matter in physical things, depending on whether one is concerned with substantial or accidental change. Formal cause may be subdivided into substantial formal cause, that is, the soul of an animate being, or accidental formal cause, that is, quantity or various qualities. Efficient cause may be divided in many ways. The most important of these would be the divisions into primary and secondary; principal and instrumental; necessary and free; ultimate, intermediate and proximate; and total and partial. The final cause may be viewed as either the object of desire or the desire of the object, the end of generation or the end of the generated thing, etc. A fifth cause, of which Aquinas makes fruitful use, is the exemplary formal cause. Briefly, it is "a form, in imitation of which something comes into being from the intention of an agent that determines its end for itself" (De ver. 3.1). This is like a blueprint in the mind of an artificer, according to which some artifact is fashioned.
Causality in Modern Thought
Entering the era of modern philosophy, one experiences a consensus that is definitely antithetic to the traditional doctrine of causality. In what follows, the principal teachings of philosophers who have been most influential in this area, namely, empiricists, rationalists, and positivists, will be sketched.
BACON AND DESCARTES
Francis bacon is representative of this movement in its early stages. He appears to be interested primarily in formal causes, although these for him often serve as nothing more than laws of nature. However, at times his formal causes bear a resemblance to efficient causes. He removes final causality from the realm of natural philosophy and bequeathes it to metaphysics. For all practical purposes, he seems to have regarded final causes as an anthropomorphism that had best be purged from the field of science.
René descartes added further impetus to this general opposition to traditional causes. In making matter inert and in reducing all motion to local motion, he prepared the way for mechanism. The Cartesian view does not admit that things have intelligibility or necessity in their own right, because, as J. Maritain has rightly observed, Descartes made things depend for their intelligibility upon a divine will and not upon divine ideas. Hence, for him, final causes lead to a fruitless search and can be dismissed from human enquiry.
LOCKE AND HUME
John locke and David hume were both empiricists and nominalists, Hume being the more consistent of the two. Their rejection of causality could easily have been anticipated. However, in Locke's case, rather than reject causality outright, he preferred to relegate it, as he did substance, to the realm of the unknowable. For both Locke and Hume, all that man can know are successive phenomena.
It is primarily by Hume that the major attack is launched upon efficient causality. According to Hume, man knows only his ideas and images directly and not the world of reality. Mind is, for him, simply a state of successive phenomenal impressions and judgment is replaced by association. In asking whether causality can be justified, Hume requests that one show how its most important characteristic, necessary nexus, is grounded in experience. Not finding it rooted there, he concludes that the necessary connection between cause and effect is psychological, having its ground in custom and the association of ideas. Cause thereupon becomes a relationship among ideas and no longer an influence of one thing upon the other in the real world. However, Hume never berated the practical utility of the notion of cause; he simply maintained its speculative unverifiability. Again, for Hume, instinct is more to be trusted than reason.
The principal shortcoming of Hume's view stems from his empiricism and nominalism. He attempted to have the senses detect, in a formal way, causality and necessity per se—something that those powers are incapable of doing. Aquinas had himself observed that not even substance is sensible per se, but only per accidens. Since he did not admit abstraction of an intellectual nature, Hume was consistent within his own system in rejecting causality and substance. And, unable to justify causality ontologically, he did the next best thing in justifying it psychologically. Yet Thomas reid, of the "Common Sense" school of philosophy, disagreed violently with Hume's conclusions and reacted by making causality a first principle of knowledge.
Immanuel Kant, awakened by Hume from the "dogmatic slumber" of Wolffian rationalism, saw Hume's problem but was not content to accept his solution. For Kant, Hume's was no solution and so he himself faced the thorny problem of justifying causality. Kant's faith in Newtonian physics and mathematics required him to find an answer that would preserve the status of those disciplines. He felt no such concern for metaphysics, however.
Briefly, Kant's position is this. Man knows but the order of appearance or phenomena, not the order of things-in-themselves or noumena. Now, to know means to change the datum by locating it within a spatio-temporal relationship, whose structure is supplied by the knower through the a priori forms of sensibility. Next man must impose upon this spatio-temporal datum certain other categories that are also rooted in the knower a priori. These are the categories of the understanding (Verstand ): Quantity, Quality, Relation and Modality. Causality is contained as a subdivision of Relation. Together with the forms of space and time, these categories are constitutive of experience, as opposed to the ideas of reason (Vernunft ), which can only be regulative of experience. Previous philosophy erred in confusing the regulative function of ideas with the constitutive functions of the categories. The categories (including causality) are valid when applied to the phenomenal order, but not valid when applied beyond this to the noumenal order. To attempt the latter is to court transcendental illusion (or metaphysics, as Kant understood it). Nevertheless, such a tendency is natural to man and he must always be wary lest he give in to it.
Since Kant allowed a valid but restricted use of causality and other categories within the phenomenal order, he felt that he had preserved the legitimate character of the positive sciences. But maintaining the inapplicability of such categories to the noumenal order led Kant to conclude that metaphysics was impossible as a science. For Kant, then, man does not discover causality in the order of things; rather, he prescribes it and imposes it upon the phenomena in order to render them intelligible (Prolegomena to Any Future Metaphysics, a. 36). Interestingly enough, Kant himself refers causality to the noumenal order, an error he specifically warns against (confer, Prolegomena, a. 13, Remark 2, and Critique of Pure Reason, Introduction, 1). While Kant's general position is understandable in the light of his conceptualism, it is not amenable to a philosophy of moderate realism.
Hegel renders Kantian thought more idealistic, accounting for causality by an unfolding of Absolute Mind, although the process is somewhat obscure. To a considerable extent, the Cartesian demand for clear and distinct ideas and for certitude is at the root of the denial or misunderstanding of causality in modern philosophy. It is true that causality is fundamentally a mystery and therefore lacks the clarity one might desire as an optimum. But opaque though it may be, its certitude is guaranteed by man's direct insight into the real. That this insight is limited can readily be granted.
POSITIVISM AND MODERN SCIENCE
In the main, contemporary philosophy follows the pattern set by its predecessors. positivism accepts causality only as invariable sequence, and this is really to deny its acceptance. pragmatism, while granting the usefulness of the concept of cause, remains close to positivism. Current scientific empiricism generally regards causality as a convention. Representative of both positivism and scientific empiricism, Moritz Schlick of the Vienna Circle says, "The sentence: 'A follows necessarily from B,' so far as content is concerned, is completely identical with the sentence: 'In every case where the state A occurs, the state B follows,' and says nothing more whatsoever"(Philosophy of Nature, tr. A. Van Zeppelin, New York 1949, 89). Charles Sanders peirce reduced efficient cause to its effect and its effect to an irreducible fact. Thus, for him, there are only facts. "The existence of a fact is equivalent to the existence of its consequence. Thus if the consequences of a supposed fact exist, then, so does the supposed fact for the pragmatist"(Values in a Universe of Chance, ed. P. Wiener, Garden City, N.Y. 1958, 129). Rudolf Carnap and Phillip Frank look upon cause as a convention; A. S. Eddington, L. Boltzmann, and E. Mach see nature as acausal.
With the increasing mathematization of the sciences, causality is rapidly losing all dynamical significance and becoming more statistical. Contributing to this view is the current tendency among modern scientists to investigate logical constructs, instead of the world of reality itself. Yet there are indications of a resurgence of interest in causality among philosophers of science such as Mario Bunge and perhaps the future will see a reinstatement of traditional notions.
The principle of causality must be seen and grasped in the sensory order, but by an intellectual rather than by a sensory act (see causality, principle of). Consequently, nominalism and empiricism, in denying such an ability to man, are logically forced to deny causality as having no more than psychological value. Conceptualism is itself little more than a refined associationism, a position whose depths were adequately plumbed by Hume. Hence, unless one grants the epistemological position of moderate realism, they will be led to reject causality as metaphysically and scientifically unverifiable. Yet the doctrine of causes is of greatest importance, not only for philosophy and theology, but for the sciences as well. Causality is precisely what enables these disciplines to discern connections and acquire certitude, instead of merely accumulating facts. The manipulation of nature does not require such a doctrine, but an understanding of nature does. For without causality, man necessarily becomes limited to the order of opinion and thereby hopelessly frustrated in his quest for knowledge.
See Also: metaphysics; metaphysics, validity of; instrumental causality
Bibliography: g. b. klubertanz and m. r. holloway, Being and God (New York 1963). j. f. anderson, The Cause of Being (St. Louis 1952). f. x. meehan, Efficient Causality in Aristotle and St. Thomas (Washington 1940). m. a. bunge, Causality (Cambridge, Mass. 1959). v. f. lenzen, Causality in Natural Science (Springfield, Ill. 1954). e. nagel, The Structure of Science (New York 1961). a. guzzo and f. barone, Enciclopedia filosofica, 4 v. (Venice-Rome 1957) 1:957–975. a. e. michotte, La Perception de la causalité (2d. ed. Louvain 1954).
[g. f kreyche]
In economics and the social sciences the value of many variables (such as price of a product, crime rate, level of illiteracy, personal income, and consumption) is observed with great regularity. As a result, an empirical generating mechanism can be postulated that produces the observed values of the variable of interest. The investigation and understanding of this mechanism is one of the main tasks for social scientists and by doing so the issue of causation inevitably arises. Causation can be discussed in very general, abstract terms or the discussion can focus on the specific question of whether or not it is possible to test for causation using the data available.
The latter requires an operational procedure and definition (mechanisms and subsystems) and this formulation arises because of a lack of understanding of the working of a complex system. In this formulation, each mechanism, which might be represented by an equation, determines the value of a particular variable as a function of some others. The variable whose value is so determined (dependent or endogenous variable) is called the effect of the working of that particular mechanism, while the values of other variables entering into the mechanism (independent or exogenous variables) are the causes of that effect.
As a specific example, theoretical analysis may say that “y is a function of x,” that is, changes in the independent variable x generate changes in the independent variable y. One might write this as y = f (x ). Empirical analysis then attempts to estimate the actual strength of the relationship between y and x. So, empirical seeks to uncover the data generating mechanism y = β 0 + β 1 x. Hence, if x increases by 1 unit y will increase by β 1 and if x = 0 then y = β 0.
Much of economics and social science is concerned with cause-and-effect propositions insofar as these disciplines pose causal relationships that postulate that a dependent variable’s movements are causally determined by movements in a number of specific independent variables. However, one should not be deceived by the words dependent and independent. Although many theoretical economic relationships are causal by their nature, statistical analysis, for example linear regression, cannot prove causality. All regression analysis can do is test whether a significant quantitative relationship exists, measure the strength of this relationship, and postulate the direction of the quantitative relationships involved. Regression analysis cannot confirm causality. Judgments referring to causality are made through various causality tests.
The objective of any causal analysis is to try to influence the degree of belief held by an individual about the correctness of some causal theory. Hence, the task of the analysis is not to be complete in itself, but rather to have enough value to make one consider one’s belief. There are basically two types of causal testing situations. In a crosssectional causality analysis the question asked is why this variable behaves differently from the other. In a temporal causality analysis the question asked is why this variable changes behavior from period to period. Although many important economic questions can be phrased in the cross-section causal situation, they have received little causal testing in that context and many tests have been conducted for economic questions that can be stated as temporal causation. The definitions of causality and their interpretations may differ between cross-section and time-series cases. In all cases, however, the classification of variables into exogenous and endogenous and the causal structure of the mechanism (econometric model) are under scrutiny.
The relation between exogeneity and causality is the heart of any investigation into causal analysis. There are a number of definitions of exogeneity: weak, super, and strong exogeneity. A variable is said to be weakly exogenous for estimating a set of parameters if inference on the parameters conditional on this exogenous variable involves no loss of information. The concept of superexogeneity is related to the Lucas critique, which states that if a variable is weakly exogenous and the parameters in the equation remain invariant to changes in the marginal distribution of the variable, then the variable is said to be superexogenous. A variable is strongly exogenous if it is weakly exogenous and at the same time is not preceded by any of the endogenous variables of the model. The concept of strong exogeneity is linked to the concept of Granger causality, and should be considered as a test of precedence rather than causality as such. Hence, a variable is defined to be strongly exogenous if it is weakly exogenous and it is not caused by any of the endogenous variables in the Granger sense. However, in the usual simultaneous equations literature there is doubt as to what extent the test for Granger noncausality is useful as a test for exogeneity. Nevertheless, some argue that Granger noncausality is useful as a descriptive device for time-series data.
The Granger causality test is based on two axioms, that the cause will occur before the effect and that the cause contains unique information about the effect. In practice, Granger causation tests whether A precedes B, or B precedes A, or they are contemporaneous. It is not a causality analysis as it is usually understood and in this limited sense Clive Granger (1969) devised some tests which proceed as follows: consider two time series, xi and yi. The series xi fails to Granger cause yi if in a regression of yi on lagged y ’s and x ’s, the coefficients of the latter are zero. The lag length is, to some extent, arbitrary. An alternative test provided by Sims states that xi fails to cause yi in the Granger sense if in a regression of yi on lagged, current, and future x ’s, the latter coefficients are zero. Although between the two tests there are some econometric differences, the two tests basically test the same hypothesis of precedence. This is the reason that many econometricians have suggested the use of the term precedence rather than Granger causality, since all one is testing is whether or not a certain variable precedes another and one is not testing causality as it is usually defined and understood.
The causality issue arises also in forecasting problems and techniques. Forecasting is the prediction of the behavior of future events and causal models are used to derive numerical forecasts. The causal models are regression and autoregression models used to produce numerical time series forecasts. The subject of a causal model is to identify one series as the main series of interest and to use another series as the predictor for the main series. It is argued that economic theory is necessary in order to provide the information needed to specify the causal relationships, because forecasts may not involve causal relationships.
In a general formulation of a causal time series model the predictor variable (exogenous) enters the equation at the same time as a contemporaneous variable and as a lagged independent variable. Even a simple causal model is fraught with difficulties. This is typically due to the problem of distinguishing the autocorrelation between the dependent and independent variables from the cross-sectional correlation between the two. Cross-sectional correlations that appear significant but are induced by autocorrelations are called spurious correlations. The problem of spurious correlation arises because in many instances, the predictor variable is stochastic and thus we need to forecast its time series. Several causal models have been developed to cope with this problem and the most common is the regression model with autoregressive disturbances.
The estimation of the causal effect arises also in the case of random experimentation. The central idea of an ideal randomized experiment is that the causal effect can be measured by randomly selecting observations from a population and then randomly giving some of the observations a treatment, the causal effect of which researchers then investigate. If the treatment is assigned at random then the treatment level is distributed independently of any of the other determinants of the outcome, thereby eliminating the possibility of omitted variable bias. The causal effect on Y of treatment level X is a difference in expected values and thus is an unknown characteristic of a population. One way to measure the causal effect is to use data from a randomized control experiment. Because the treatment is randomly assigned, the causal effect can be estimated by the difference in the sample average outcomes between the treatment and control groups.
Despite the advantages of randomized controlled experiments, their application to economics faces severe hurdles, including ethical concerns and cost. The insights of experimental methods can, however, be applied to quasi experiments that provide ecometricians with a way to think about how to acquire new data sets, how to manipulate instrumental variables in their analysis, and how to evaluate the plausibility of the exogeneity assumptions that underlie Ordinary Least Squares (OLS) and instrumental variables estimation. In a quasi-experiment technique there are special circumstances that make it seem “as if” randomization has occurred. In quasi experiments, the causal effect can be estimated using a differences-in-differences estimator, possibly augmented with additional regressors; if the “as if” randomization only partly influences the treatment, then instrumental variables regression can be used instead. An important threat confronting quasi experiments is that sometimes the “as if” randomization is not really random, so the treatment (or the instrumental variable) is correlated with omitted variables and the resulting estimator of the causal effect is biased.
The issue of causality is very important in economic and social analysis but unfortunately not all analysts give the same meaning to this word. In discussing causal links, many economists emphasize the relevance of a sound economic theory in deriving causal propositions and they argue that caution should be applied in the inferences derived from the analysis.
SEE ALSO Instrumental Variables Regression; Natural Experiments; Reflection Problem; Regression; Seemingly Unrelated Regressions; Selection Bias; Simultaneous Equation Bias
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Granger, Clive W. J. 1969. Investigating Causal Relations by Econometric Models and Cross-Spectral Methods. Econometrica 37: 424–438.
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