Home > Encyclopedia of Science and Religion > Causation

The notion of cause is one of the most common yet thorniest concepts in the history of philosophy. This should come as no surprise. Questions of causation tie up with such divisive issues as determinism and moral responsibility, as well as with the principle of the causal closure of the physical universe and the possibility of divine action. Furthermore, causation is intimately intertwined with the notion of change. Together these two notions stood at the cradle of such momentous intellectual traditions as Western philosophy in Asia Minor, the Vedic hymns and the Upanishads in Central and South Asia, and early Buddhism along the borders of the ancient Ganges. They constituted the first and fundamental challenge to systematic thought, inspiring a variety of solutions still resonating in intellectual debates.

People use causal idiom in everyday life with great ease, yet upon closer scrutiny this family of notions seems to defy analysis and justification. The famous comment of Augustine of Hippo (354–430) regarding the question of time applies with equal force to the analogous question concerning causation: When nobody asks us, we know what it means; when queried, we don't.

Quite generally, a cause produces something called the effect; and the effect can be explained in terms of the cause. Usually the effect is taken to be a change in something already existing. Yet in traditional theology it has also been assumed that causes may give rise to new substances out of nothing. Thus in the Judeo-Christian tradition God is seen as the creator of the universe, which God created out of nothing. Similarly, theories of self-causation and creation by God were two of the major causal theories in the Vedic tradition. By contrast, early Buddhism rejected these two views, arguing that the idea of self-causation would imply the prior existence of the effect, while the idea of external causation would imply the production of a nonexistent effect out of nothing. Similarly, Thomas Aquinas (c. 1225–1274) rejected the theological notion of self-causation as philosophically untenable. God cannot possibly be regarded as causa sui, he argued, since either God existed to cause God, in which case God did not need to cause God; or else God did not yet exist, in which case God could not be anything to be able to cause God.

Aristotle's theory of causation

Aristotle (384–322 B.C.E.), too, regarded causes as producing changes in preexisting substances only. To be sure, when a moth emerges from a caterpillar the change is so striking that a new word is naturally used for the causal product. And yet the moth emerged from the pre-existing caterpillar. By contrast, when a leaf turns red, it is still called a leaf, because the change is less striking. Aristotle called the former type of change generation, as opposed to the merely qualitative change—or, in his terminology, motion (kinesis)—taking place in the latter kind of case. Yet the distinction is plainly a relative one, opposing rather than licensing the idea of new substances being producible out of nothing by a cause. Indeed, the conception of creation ex nihilo is foreign to the whole tradition of ancient Greek thought.

Commenting on Plato (428–347 B.C.E.) as well as on his pre-Socratic predecessors, Aristotle famously distinguished four types of causes or explanatory principles (the Greek word aitia is ambiguous between these two rather different meanings). A statue of Zeus, for example, is wrought by a sculptor (its efficient cause or causa efficiens, also known as the causa quod) out of marble (the material cause or causa materialis), which thereby takes on the shape the artist has in mind (the formal cause or causa formalis) in order that it may serve as an object of worship (the final cause or causa finalis, also known as the causa ut). Plato's forms, or formal causes (causa exemplaris), had been transcendent ideas in the mind of the Demiurge. By contrast, in Aristotle's theory of natural change the four causes together have an immanent teleological character. The form being developed is an integral part of the thing itself. Thus, the formal cause for an acorn developing into an oak tree is the seed's intrinsic character disposing it to become an oak tree rather than, say, a maple tree.

Naturally Aristotle's largely teleological theory of causation authorized the abundant use of final causes in explanations of natural phenomena. Thus his theory of motion espoused the principle that objects strive toward their locus naturalis, while medieval hydraulics—just to give another example—promulgated the principle that nature abhors a vacuum (Natura abhorret vacuum).

Mechanicism and the demise of the teleological theory of causation

While medieval scholastic thought was still dominated by Aristotle's theory of causation, seventeenth-century science opposed its teleological underpinnings. Natural order and change, it claimed, could be produced by "blind" efficient causation alone, without the need of final or formal causes intervening in the process. Having created the matter of the universe together with the laws of mechanics, God could have left the world to its own in any disordered fashion, claims René Descartes (1596–1650) in Le Monde, and yet in due course the universe would have taken on its current natural order of celestial motions and "terrestrial" physics mechanically, driven blindly by efficient causes alone and without "striving" to achieve any final perfections or divine purposes.

This conception of the causal "machinery" of the universe being limited to efficient causation presented a stimulating and exceedingly fruitful research program to modern science. In due course its validity was proclaimed to extend not just to mechanics proper, but also to physiology and chemistry, to biology (in the Darwinian program), to ethology, and even to the realm of human action in twentieth-century sociobiology and of human thought in late-twentieth-century cognitive science. And yet, from the very start, the program spawned riddles and grave philosophical difficulties. Chief among these was the difficulty involved in the widely held view that linked (efficient) causation to necessity. David Hume (1711–1776) notoriously pointed out that causal pairs are related neither by logical nor by empirical necessity. It is both logically and empirically possible for an effect to fail to follow a given cause. In fact Hume's influential argument had a theological background. French theological tradition, including notably Descartes and Nicolas Malebranche (1638–1715), had always been keen to stress the point that God's freedom is unfettered by any restrictions whatsoever. Hence given any cause, God is always free not to permit the effect to follow. Thus, causes alone, unaccompanied by the will of God, are never sufficient conditions for their effects. Nor, given God's omnipotence, can they be allowed to be necessary conditions for their effects. For God is free to bring about the effect by any other mediating cause or even by simply willing it.

Having failed to find an empirical basis for the idea of necessary connection in the case of singular causation, Hume turned his attention (without making a clear distinction) to the case of causation as it exists between classes of (similar) events. Analyzing this latter notion Hume advanced a regularity theory of causation. Eschewing powers and necessary connections, Hume thought causation could be adequately dealt with in terms of the "constant conjunction" of similar causes with similar effects. In addition, conditions of temporal priority and spatiotemporal contiguity were also required. This analysis, in Hume's view, had the distinct merit of being entirely empirical. Yet subsequent generations of (logical) empiricists have found, to their exasperation, that the empiricist ideals are not that easily fulfilled.

One difficulty is that of distinguishing between accidental and genuinely causal regularities. As the Scottish philosopher Thomas Reid (1710–1796) famously remarked in his Essays on the Active Powers of the Human Mind (1788), day is invariably followed by night and night by day and yet neither is the cause of the other. One tempting way to find a distinctive mark is to say that statements of causal regularities, unlike those that express merely accidental generalizations, are supported by corresponding counterfactuals. Thus, it is presumably true that a given piece of metal would have expanded had it been heated. By contrast, even if all the marbles in a given bag happen to be red, that fact alone doesn't add credence to the counterfactual that had the green marble in my hand been a marble in that bag, it would have been red. Yet, reliance on counterfactuals would involve a high price for empiricists to pay. For the truth conditions of counterfactuals are notoriously beyond the reach of empirical verification.

Another difficulty was raised by Bertrand Russell (1872–1970), who noted that in order for events to be causally connected they must be similar not just in arbitrary respects, but in relevant respects. For example, two matches may differ only in color or, alternatively, only in one being wet while the other is dry. Yet for the question of whether striking them will cause them to ignite only the latter dissimilarity counts while the former is entirely irrelevant. But how is one going to specify this notion of relevance? One is tempted to rely on an undefined notion of causal relevance. But that would critically trivialize Hume's analysis because it would utilize the notion of causation in the very attempt to analyze it.

Oriental theories of causation

For Hume, then, the idea of causation, insofar as it is mistakenly bound up with such unfounded notions as power or necessary connection, does not represent anything objective. The implied idea of necessity does not arise from anything in the external world. Rather it results from a mental response to the constant conjunction of causes and their effects. By comparison, in Indian philosophy the objectivity of causation has been subject to considerable shifts of opinion. The first to deny the principle of causation was the idealist school of the Upanishads. Insisting that reality and soul (atman) were permanent and eternal, they denied change and therefore causation. Like Hume, but for different "Parmenidean" reasons, these thinkers considered change and causation mental constructs, or purely subjective phenomena. Conversely, the consequent denial of atman or self among early Buddhist materialists led to fruitful speculation regarding causality and change. However, in their extreme aversion to the idealist metaphysics of the Upanishads, these materialists went on to deny all mental phenomena. This annihilationism is opposed to the earlier belief of Upanishad philosophers in eternalism. However, according to the "middle path" preached by the Buddha, both positions are errors stemming from two opposite extremes with regard to causation, which early Buddhism set out to steer clear of: on the one hand the belief in self-causation, resulting in a belief in eternalism; on the other the belief in external causation, fostering a belief in annihilationism. While early Buddhism, like Hume, rejected the belief in a mental substance or "self," it did not share his conclusion that "were all my perceptions remov'd by death [ … ] I shou'd be entirely annihilated … " (Hume, p. 252). The reason for this is precisely that unlike Hume early Buddhism insisted on the objective validity of causal processes, which it referred to as constituting the "middle" between the two extremes of eternalism and annihilationism. Consequently it regarded such causal processes sufficient for sustaining the continuity of a thing without positing a "self" or a "substance."

The importance of causality as an objective category in early Buddhism is brought out clearly by the fact that of the four noble truths discovered by the Buddha, the second and the third refer to the theory of causation. In the early Pali Nikayas and Chinese Agamas causation is not a category of relations among ideas but represents an objective ontological feature of the external world. Yet there has been much debate concerning the notion of avitathata, the second characteristic of the causal nexus in Buddhist philosophy. The Buddhist philosopher Buddhaghosa (late fourth and early fifth centuries C.E.) rendered this concept as "necessity," while others have championed a rather deflationary Humean interpretation of mere regularity and constant conjunction. From a more balanced perspective, what seems to be at stake in such discussions is to free causation from strict determinism. Thus a fourth characteristic of causation, idappaccayata or conditionality, is supposed to place causality midway between fatalism (niyativada), or unconditional necessity, and accidentalism (yadrc-chavada), or unconditional arbitrariness. Clearly, the underlying concern here is the problem of moral responsibility, which Buddhist thinkers are anxious to uphold.

Volitional causation

Taking their clue from Hume that causality is not a physical connection inasmuch as one never observes any hidden power in any given cause, philosophers of an empiricist bent have insisted ever since on analyses of causality in terms of necessary and sufficient conditions for the applicability of the term. Thus, they focused on the logical and linguistic aspects of the notion of causality to the neglect of trying to find a physical connection between cause and effect. An example is John L. Mackie's (1917–) sophisticated regularity account in The Cement of the Universe (1974).Yet the contrary opinion has not been without its adherents. Even before Hume, John Locke (1632–1704), while discussing causality, appealed to the model of human volition. When one raises one's arm, he argued, one is directly aware of the power of one's volition to bring about the action.

This purposive perspective on causation has independent merits. For one thing it can make perfectly good sense of singular causation. For another, it avoids the vexing problem of so-called causal asymmetry. The fact that one ordinarily refuses to allow effects to precede their causes—Hume's condition of the temporal priority of causes—may on this view simply be seen as a natural consequence of the familiar experience that whatever actions one initiates cannot bring about the past. In fact, this volitional model of causation has been more influential than is generally acknowledged even among protagonists of the scientific revolution. Thus Isaac Newton (1642–1727) toyed with, and George Berkeley (1685–1753) championed, a theological construal of gravitation. Instead of invoking gravitational action-at-a-distance, a notion that Newton himself had deemed embarrassing enough to keep his theory locked up in a drawer for almost twenty years, it was, according to this view, God's own intervention that caused the sun ever so slightly to drift toward such large but immensely distant planets such as Jupiter, in accordance with mathematical patterns and laws that Newton had the genius to unravel. Needless to say, such animistic astronomy fails to carry conviction at the present time. But it is good to realize, if only for expository purposes, that Berkeley's animistic world is not a world without causation. Rather it is a world where all causation is volitional. When this world is stripped of volitional causation, what remains is a "Hume world," a world truly without causation. If philosophers have found such a world equally unconvincing, they could then ask the critical question: What crucial ingredient is the Hume world lacking that our world supposedly possesses?

Recent debates: realist vs. pragmatist views on causation

Apparently there are at least two ways to go from there: One can follow either the realist or the Kantian-pragmatist way out. The opposition in question is neatly exemplified by two contemporary schools of thought on causation, one represented by Wesley Salmon (1925–2001), the other highlighted by the philosophy of Philip Kitcher (1947–). Salmon has argued that there does exist, after all, an empirically verifiable physical connection between cause and effect. It is to be found in the notion of a causal process, rather than in that of a causal interaction, which Hume mistakenly took as his paradigm. Furthermore, thanks to the theory of relativity that sets an upper limit to the transmission of causal signals, we can now empirically distinguish between genuinely causal processes (e.g., light rays traveling at straight lines from a rotating beacon to the surrounding wall of, say, the Colosseum) and mere pseudoprocesses (e.g., a spot of light "traveling" along the inner wall of the Colosseum as a result of a central beacon rotating at very high speed). While pseudo-processes may travel at arbitrarily high velocities, they cannot transmit information as only causal processes can. Similarly, the actions of a cowboy on a cinema screen are pseudoprocesses. When, in excessive excitement, you shoot him, it has no lasting effect on the cowboy, but only on the screen. Thus, in Salmon's view, the capacity to transmit information (or rather, conserved energy) constitutes empirical proof that the relevant process is genuinely causal in nature rather than a mere pseudoprocess.

According to this realist view, therefore, causation is a robust physical ingredient within our world itself, entailing necessary and sufficient conditions (or causal laws, probabilistic or otherwise), rather than being entailed by these. Causation is essentially a "local" affair, depending on the intrinsic features of two causally related events. By contrast, causal laws and necessary and sufficient conditions are "global" features, depending on the world as a whole. Consequently, on this realist view, causality may be entirely compatible with indeterminism, while theories couched in terms of necessary and sufficient conditions run into grave difficulties when confronted with the pervasiveness of indeterminacy in the subatomic realm.

Yet Salmon's theory has not been without its detractors. Thus, having confronted the theory with ingenious counter examples, Kitcher has argued that Salmon's theory, just like the empiricist theories before him, ultimately comes to rest on the truth of empirically unverifiable counterfactuals. By contrast, Kitcher's own theory places causality squarely within a Kantian-Peircian perspective. Immanuel Kant (1724–1804), while conceding to Hume that causality may be unobservable in the physical world, contradicted Hume's conclusion that therefore causality is not a real feature of the world as we know it. Indeed, causality may not be a feature positively discoverable in what Kant called the noumenal world, that is, the world as it exists in itself, without regard to the structural limitations of human knowledge. But then again, nothing is so discoverable or attributable. And yet causality is a property objectively ascribable to the phenomenal world, that is, the world as structured by the conceptual and perceptual features inherent in human cognitive capacities. As a result of the necessarily synthetic activities of human reason, one cannot conceive of the empirical world except in terms of causes and effects. The causal relation is therefore as firmly and objectively established as are space and time, which constitute the a priori forms of perception of the empirical world. These are all verifiable attributes of the physical world, which is part of the phenomenal world, the only kind of world humans are capable of knowing in principle.

Thus, the fundamental notion of causation receives a distinctly epistemological underpinning in Kantian philosophy. This is what ties Kitcher's philosophy of causation in part to the Kantian tradition. Thus, Kitcher has stated that the because of causation derives from the because of explanation. Rather than being an independent metaphysical notion, what may and may not be recognized as truly causal relations depends in the final analysis on epistemological constraints. In Kitcher's view the ultimate aim of science is to generate theories of the universe as unified and simple (or all-encompassing) as possible. Which theories are finally recognized—in the ideal end of inquiry, to borrow the famous words of the pragmatist Charles Sanders Peirce (1839–1914)—as optimally unified and robust thus determine what causes are recognized as genuinely operative and effective in the only world humans can possibly come to understand. Thus, in Kitcher's view, the metaphysical significance of causation ultimately derives from its key role in the best possible theory of the universe we will be able to generate. In a sense, therefore, causation, rather than being a metaphysically realist notion, is better seen as an unadulterated epistemological notion, dependent not on what we stumble upon in observation of singular cases of causation, as realists like Salmon would have it, but rather on the excellency of the theories that best account for the physical features of the world as a whole.

See also DOWNWARD CAUSATION; UPWARD CAUSATION

THEO C. MEYERING