Efficient causation: Our debt to Aristotle and Hume

Causation is now commonly supposed to involve a succession that instantiates some lawlike regularity. This understanding of causality has a history that includes various interrelated conceptions of efficient causation that date from ancient Greek philosophy and that extend to discussions of causation in contemporary metaphysics and philosophy of science. Yet the fact that we now often speak only of causation, as opposed to efficient causation, serves to highlight the distance of our thought on this issue from its ancient origins. In particular, Aristotle (384-322 BCE) introduced four different kinds of “cause” (aitia): material, formal, efficient, and final. We can illustrate this distinction in terms of the generation of living organisms, which for Aristotle was a particularly important case of natural causation. In terms of Aristotle’s (outdated) account of the generation of higher animals, for instance, the matter of the menstrual flow of the mother serves as the material cause, the specially disposed matter from which the organism is formed, whereas the father (working through his semen) is the efficient cause that actually produces the effect. In contrast, the formal cause is the internal principle that drives the growth of the fetus, and the final cause is the healthy adult animal, the end point toward which the natural process of growth is directed.

From a contemporary perspective, it would seem that in this case only the contribution of the father (or perhaps his act of procreation) is a “true” cause. Somewhere along the road that leads from Aristotle to our own time, material, formal and final aitiai were lost, leaving behind only something like efficient aitiai to serve as the central element in our causal explanations. One reason for this transformation is that the historical journey from Aristotle to us passes by way of David Hume (1711-1776). For it is Hume who wrote: “[A]ll causes are of the same kind, and that in particular there is no foundation for that distinction, which we sometimes make betwixt efficient causes, and formal, and material … and final causes” (Treatise of Human Nature, I.iii.14). The one type of cause that remains in Hume serves to explain the producing of the effect, and thus is most similar to Aristotle’s efficient cause. And so, for the most part, it is today.

However, there is a further feature of Hume’s account of causation that has profoundly shaped our current conversation regarding causation. I have in mind his claim that the interrelated notions of cause, force and power are reducible to more basic non-causal notions. In Hume’s case, the causal notions (or our beliefs concerning such notions) are to be understood in terms of the constant conjunction of objects or events, on the one hand, and the mental expectation that an effect will follow from its cause, on the other. This specific account differs from more recent attempts to reduce causality to, for instance, regularity or counterfactual/probabilistic dependence. Hume himself arguably focused more on our beliefs concerning causation (thus the parenthetical above) than, as is more common today, directly on the metaphysical nature of causal relations. Nonetheless, these attempts remain “Humean” insofar as they are guided by the assumption that an analysis of causation must reduce it to non-causal terms. This is reflected, for instance, in the version of “Humean supervenience” in the work of the late David Lewis. According to Lewis’s own guarded statement of this view: “The world has its laws of nature, its chances and causal relationships; and yet — perhaps! — all there is to the world is its point-by-point distribution of local qualitative character” (On the Plurality of Worlds, 14).

Admittedly, Lewis’s particular version of Humean supervenience has some distinctively non-Humean elements. Specifically — and notoriously — Lewis has offered a counterfactural analysis of causation that invokes “modal realism,” that is, the thesis that the actual world is just one of a plurality of concrete possible worlds that are spatio-temporally discontinuous. One can imagine that Hume would have said of this thesis what he said of Malebranche’s occasionalist conclusion that God is the only true cause, namely: “We are got into fairy land, long ere we have reached the last steps of our theory; and there we have no reason to trust our common methods of argument, or to think that our usual analogies and probabilities have any authority” (Enquiry concerning Human Understanding, §VII.1). Yet the basic Humean thesis in Lewis remains, namely, that causal relations must be understood in terms of something more basic.

And it is at this point that Aristotle re-enters the contemporary conversation. For there has been a broadly Aristotelian move recently to re-introduce powers, along with capacities, dispositions, tendencies and propensities, at the ground level, as metaphysically basic features of the world. The new slogan is: “Out with Hume, in with Aristotle.” (I borrow the slogan from Troy Cross’s online review of Powers and Capacities in Philosophy: The New Aristotelianism.) Whereas for contemporary Humeans causal powers are to be understood in terms of regularities or non-causal dependencies, proponents of the new Aristotelian metaphysics of powers insist that regularities and dependencies must be understood rather in terms of causal powers.

Should we be Humean or Aristotelian with respect to the question of whether causal powers are basic or reducible features of the world? Obviously I cannot offer any decisive answer to this question here. But the very fact that the question remains relevant indicates the extent of our historical and philosophical debt to Aristotle and Hume.

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