Activity in creatures, even in immanent operations, is always causality; for they cannot exercise their activity without producing new modifications. Acts of understanding and will are the exercise of an immanent activity, and yet they modify us in different ways. When we think or will we are in a different manner from that in which we are when we do not think or will; and when we pass from thinking or willing one thing to think or will another, this transition cannot take place without our experiencing new modes of being.
87. In what does the relation of efficient causality consist? What is the meaning of the dependence of the effect in relation to the cause? This is a difficult and a profound question; one of the most difficult and most profound which can be presented to science. The majority of men and even of philosophers imagine that they can solve it, by using words which, rightly analyzed, explain nothing.
88. To cause, it is said, is to give being. What means to give? To give is here synonymous with to produce. What means to produce? With this the explanations are at an end, unless one should wish to fall into a vicious circle, saying that to produce is to cause or give being.
A cause, it is also said, is that from which a thing results. What is understood by resulting? To emanate. What is to emanate? To emanate is to proceed, to flow from another. Always the same thing: metaphorical expressions which at bottom have all the same meaning.
It is said that a cause is that which gives, produces, makes, communicates, generates, etc., and that an effect is that which receives, proceeds, emanates, results, flows, comes, springs, etc.
89. Causality implies succession, but is not identified with it. We can clearly conceive that B is after A, without A being the cause of B.
Internal and external experience present continual examples of succession distinct from causality. A man goes out into the field, another follows him: between the going out of both there is succession, but there may be no causality. The two phenomena, whether considered objectively in themselves, or subjectively, as known by us, are connected by the relation of succession, but not by that of causality. There is as great a difference in philosophy as in ordinary language between post and propter, after and because of. The same is true in purely internal phenomena. I think of a question of philosophy, and then pass to a literary question: the two thoughts are successive, but one is not the cause of the other.
90. The relation of causality is not the connection of the ideas of things. The representations of A and B may be strongly connected in our mind without our even thinking of the relation of causality. We have seen in a place a scene which made a profound impression on us; ever afterwards the remembrance of the place recalls the scene, and the recollection of the scene reminds us of the place; here we find two internal representations strongly connected, without our therefore attributing to the objects the relation of causality. We know that two persons arrive at the same place and without the coming of the one influencing the coming of the other. The idea of the coming of the one will be associated in the mind with the idea of the coming of the other. There will then be a connection of representations, although we deny to the objects the relation of causality.
91. Although the connection of the ideas in our understanding may, in consequence of a constant experience, be such that one is always preceded by the other, as the conditioned is by the condition, this is not enough for true causality. An observer may have remarked the correspondence of the ebb and flow of the tide with the motion of the moon; but whether for reasons of philosophy, or because it has never occurred to him that the motion of the moon could influence the motion of the sea, he considers these phenomena entirely independent of one another, although he may try hard to explain so strange a coincidence. In the mind of this observer the two phenomena will be always joined, in such a way that the phenomenon of the moon will always be that of the ebb and flow, without its being possible to invert the order and make the ebb and flow precede the motion of the moon. Here then is a necessary priority in an idea, and yet true causality is not attributed to the object.