Reid, Thomas (1710–1796)

3. Causality

Reid maintains that only beings which, by their active power, produce some change in themselves or in some other being are properly called causes and agents (1788: I). Moreover, whatever is the effect of active power must be something that is contingent, dependent upon the power and will of its cause. Power to produce an effect supposes power not to produce it, otherwise it is necessity, which is incompatible with power taken in the strict sense. Reid concedes that there is another sense of the term cause, so well authorized by custom that we cannot always avoid using it. He proposes to James Gregory (see Reid 1895) that we call it the ‘physical’ sense, as when we say that heat is the cause that turns water into vapour. A cause, in this sense, means only something which, by the laws of nature, the effect always follows. There is yet another sense of the term ‘cause’ that Reid allows to have currency and which he distinguishes from the sense just explained. Specifically, laws of nature may be called ‘physical’ causes too; but note that they do not bring about anything unless put to work either by some agent or by some physical cause.

Why does Reid maintain that physical causes are not true causes? One reason is that they cannot be ultimate. Thus, that a body put in motion continues to move until stopped might be viewed as an effect of an inherent property of matter, and so as not physically ultimate. If so, we may say that that property of matter is the physical cause of the continuing motion; but surely the ultimate cause of this is the being who gave the inherent property to matter. Alternatively the continuing motion may be viewed as an arbitrary appointment of the Deity, and may then be called a law of nature and a physical cause. But such a law requires a being to enact it.

Must that being be an agent? Reid answers (1788: IV.ii) by invoking as a first principle the thesis ‘that neither existence, nor any mode of existence, can begin without an efficient cause’, from which it follows ‘that everything which undergoes any change must either be the efficient cause of that change in itself, or it must be changed by some other efficient’. Reid adds that we can only conceive kinds of active power similar or analogous to the kind we attribute to ourselves, which is exerted by will and with understanding.

Again, consider the notion of a physical cause as something which, by the laws of nature, the effect always follows. Now given this account it would seem that, on Reid’s view, the existence of such causes is, at best, contingent. Thus he says that the conjunction between a physical cause and its effect must be constant, unless in the case of a miracle, or suspension of the laws of nature. Moreover, processes such as evaporation are frequently interrupted in quite ordinary ways. Finally, it is clear that this account of physical causes will not, of itself, suffice to deal with the problem that Reid left for regularity accounts of physical causation, namely that, according to them, day is the cause of night and night of day.

Let us now turn to consider Reid’s account of how physical causes are to be discovered. Reid (1785: I) adopts a Newtonian view on this question (see Newton, I.), maintaining that if anyone claims to show us the cause of any natural effect, whether pertaining to matter or to mind, we must first consider whether there is sufficient evidence that the cause really exists. If there is not, it should be rejected as a fiction. If it does really exist, we are to consider next whether the effect necessarily follows from it. And, Reid adds, conjectures about causes should be treated as ‘reveries of the vain’. However, writing to Kames (see Home, H.), he allows that such conjectures can have definite value in the following way. Attending to a given phenomenon, I conjecture that it may be owing to a certain cause. This may lead me to make the experiments or observations appropriate for discovering whether that is really the cause or not; and if I discover that it is or that it is not, my knowledge is improved and it is clear then that my conjecture was a means to that improvement.

The establishing of efficient causes is not within the sphere of natural philosophy, the method of which is experimental and leads to the establishing of physical causes at best. Indeed, Reid writes to Kames (see Reid 1965), apart from the fact that our nature leads us to believe ourselves to be the efficient causes of our own actions, and that from analogy we judge the same of other intelligent beings (with the result that attributions of human action are outside the sphere of natural philosophy) we are left, for the establishing of efficient causes, with nothing but resort to such first principles as that every beginning of existence has an efficient cause, and that an effect which has the most manifest marks of intelligence, wisdom and goodness, must have an intelligent, wise and good efficient cause. And with final causes, apparently so pervasive, it is similar (see Causation).