4. CONCLUSION: IMPORTANT CHANGES IN THE MEANING OF CAUSE
In this concluding review of the results of this article, I will point out the conceptual tensions that are inherent to the historical development of the concept of cause. More specifically, I will show that two decisive milestones mark the history of causality: the Aristotelian (-scholastic) Conception (I), and the Scientific Conception (II). It will be shown that these two conceptions of cause are mutually incompatible.
(I) Aristotle conceived efficient causes as 'things responsible' in the sense that an efficient cause is a thing, which by its activity brings about an effect in another thing. Thus, the efficient cause was defined by reference to some substance performing a change: it is the "primary source of the change." That which is produced is either some new substance, such as ashes from wood, or simply a change in some property of a given substance. Furthermore, the general context of this meaning of efficient cause is teleological, for each efficient cause acts for the sake of an end. Hard work, for example, is the efficient cause of fitness, which is the end. Thus, according to the Aristotelian conception, causes are conceived as the active originators of a change that is brought about for the sake of some end.
(II) Probably the most radical change in the meaning of cause happened during the seventeenth century, in which there emerged a strong tendency to understand causal relations as instances of deterministic laws. Causes were no longer seen as the active initiators of a change, but as inactive nodes in a law-like implication chain.
This change of perspective had its antecedents in Stoicism and medieval philosophy. The Stoics were the first to associate causation with exceptionless regularity and necessity. But, contrary to the scientific conception of cause, the necessity involved in the causal relation pertained to particular events; it was thought to be necessary that the same particular effect would recur in the same particular circumstances, and that it was not possible that it would be otherwise. Aquinas went further than the Stoics by relating efficient causality to natural necessity and to law-like behavior; things belonging to the same type act similarly in similar causal circumstances. The dismissal of explanations by final and formal causation by Descartes, Francis Bacon and Galilei brought about the rejection of the Aristotelian-scholastic doctrine of active qualities and substantial forms as causal factors in natural processes. The Aristotelian idea that a substantial form be transmitted from a cause to its effect had no basis whatever in our experience of things.
However, paradoxical as it may seem, it was precisely this concept of formal cause that came to play an important role in the development of the new conception of efficient cause, according to which efficient causes were simply instances of general laws, which in turn were general, mathematical principles. But, to a large extent, the concept of law of nature was the inheritor of the concept of formal cause: both concepts were meant to explain the stability of the world. The main difference is that, whereas the formal cause was thought to explain the stability of the world by explaining the structure of things, the laws of nature were thought to explain the stability of the world by explaining the relations between things.
An important characteristic of the modern conception of cause was that causation and determinism became virtually equivalent. The crux of the debate between the rationalists and the empiricists pertained to the nature of this determination.
(IIa) In the rationalist conception of cause, the relationship between cause and effect is a logical relation. Necessitation involves implication. Thus, a complete knowledge of the causes is tantamount to knowing the premises from which by reasoning alone the effects can be deduced. Though Descartes, Hobbes, Spinoza, and Leibniz roughly shared this view, they could not avoid some basic ambiguities.
Thus, Descartes, while regarding the laws of nature themselves (instead of their instances) as efficient causes, also held the view that the relation of a cause to its effect is the relation of ground to consequent: a logical relation. On the other hand, he regarded minds as free and as particular causes, in the sense of active initiators of a change.
Hobbes's position was equally ambiguous. For, while he defended IIa (given the cause, "it cannot be conceived but that the effect will follow"), he regarded the concepts of cause and power as complementary notions (Hobbes 1655, 9.3), an idea that is characteristic of the Aristotelian conception of cause (I).
Similarly, Spinoza, perhaps the most straightforward defender of the view that necessitation involves implication, held that God is a free cause in the sense of being a real initiator of change, but that the necessary causes are necessitated by other causes and are therefore just inactive nodes in a chain, each of them logically necessitating its effects and logically necessitated by its effects.
Even Leibniz, who held the most original view of causation by rejecting the idea that the ultimate constituents of reality (the monads) have a causal relation to each other, and thus limiting causation to the links of the historical-logical chain constituting each individual substance, could not avoid one major ambiguity. For, whereas, in his view, the necessity involved in the causal relation is as strong as logical necessity (IIa), the innermost significance of causality is that of the active initiation of change (I). For, every monad is "spontaneous," that is to say, its substantial form is the only source of its modifications. Monads are real "centers of activity." Remarkably, Leibniz’ originality resulted partly from his 'reactionary' defense of both formal and final causation. Each monad behaves in accordance with its nature or substantial form, which is its original purpose, given by God. Efficient causes are therefore means to ends (I).
Thus, it may be argued that the rationalist philosophers all held some hybrid conception of cause, involving a combination of cause IIa (the identification of causes with grounds) and cause I (the originators of a change).
(IIb) To David Hume, commonly held to be the main representative of the empiricist approach to causation, our idea of causal necessity is due partly to our observation of the constant conjunction of certain objects, and partly to the feeling of their necessary connection in the mind. The habitual impression of conjunction feels like a necessitation, as if the mind were compelled to go from one to the other. The necessary connection is not discovered in the world but is projected onto the world by our minds.
However, Hume's view was far from being shared by all empiricist philosophers. Indeed, by suggesting that his fellow empiricists held the belief that necessity is synonymous with power, he seriously misrepresented their views. For, both Locke and Newton explicitly denied that the ideas of causation or power involved the idea of necessary connection according to law. According to Newton, these two notions are even mutually exclusive because complete uniformity or necessary connection would entail a denial of causal efficacy. For Locke, as for Newton, causality is related to the Aristotelian belief that causes are substantial powers that are put to work. Therefore, Hume's famous criticism only concerns the rationalist scientific conception of cause (IIa), which, from an historical perspective, is merely a derivative sense of 'cause.'
Kant's concept of cause, by which he tried reconcile the rationalist and empiricist views, is a hybrid of IIa and IIb. Because causal relations involve laws (II), Kant in effect says that an event A is the cause of an event B if, and only if, there is a universal law of the form: events of type A are necessarily followed by events of type B. But, while defending the rationalist idea that causality is an a priori conception, which involves strict universality and necessity (IIa), he also holds the empiricist view that causes precede their effects, which from the perspective of IIa (according to which, causes are contemporaneous with their effects) is utterly impossible.
Mill too conceived causal relations in terms of law-like generalizations (II). His analysis is about kinds of causes and kinds of effects. The "real cause" of an event is that set of conditions which, when they are all met, is invariably and unconditionally followed by the type described as the effect.
All in all, the complex evolution of the concept of cause from the seventeenth century on is marked by the interplay between, at least, two radically different conceptions of cause: the Aristotelian-scholastic conception, according to which causes are the active initiators of a change, and the scientific conception, according to which causes are the inactive nodes in a law-like implication chain.
Our common use of causal terms is entirely oblivious of this ambiguity. But, more deplorably, most discussions by modern philosophers have failed to see this basic duality, because the premises of those discussions are usually infected by it. For instance, the common assumption that causation is inherently linked to law-like behavior is far from obvious.
In short, my analysis of the historical development of the concept of cause shows that each analysis of causation must start from the recognition that causal propositions are ambiguous, and that (at least) two mutually exclusive meanings are to be distinguished. According to I, 'A is the cause of B' means 'A is the initiator of a change in B'; according to II, 'A is the cause of B' means 'Given the occurrence of B, A must necessarily have occurred.'