Page:Popular Science Monthly Volume 69.djvu/320

316 when a phenomenon appears to us as the cause of another, we regard it as anterior. It is therefore by cause that we define time; but most often, when two facts appear to us bound by a constant relation, how do we recognize which is the cause and which the effect? We assume that the anterior fact, the antecedent, is the cause of the other, of the consequent. It is then by time that we define cause. How save ourselves from this petitio principii?

We say now post hoc, ergo propter hoc; now propter hoc, ergo post hoc; shall we escape from this vicious circle?

Let us see, not how we succeed in escaping, for we do not completely succeed, but how we try to escape.

I execute a voluntary act $$A$$ and I feel afterward a sensation $$D,$$ which I regard as a consequence of the act $$A;$$ on the other hand, for whatever reason, I infer that this consequence is not immediate, but that outside my consciousness two facts $$B$$ and $$C,$$ which I have not witnessed, have happened, and in such a way that $$B$$ is the effect of $$A,$$ that $$C$$ is the effect of $$B,$$ and $$D$$ of $$C.$$

But why? If I think I have reason to regard the four facts $$A, B, C, D,$$ as bound to one another by a causal connection, why range them in the causal order $$A B C D,$$ and at the same time in the chronologic order $$A B C D,$$ rather than in any other order?

I clearly see that in the act $$A$$ I have the feeling of having been active, while in undergoing the sensation $$D,$$ I have that of having been passive. This is why I regard $$A$$ as the initial cause and $$D$$ as the ultimate effect; this is why I put $$A$$ at the beginning of the chain and $$D$$ at the end; but why put $$B$$ before $$C$$ rather than $$C$$ before $$B?$$

If this question is put, the reply ordinarily is: we know that it is $$B$$ which is the cause of $$C$$ because we $$always$$ see $$B$$ happen before $$C$$. These two phenomena, when witnessed, happen in a certain order; when analogous phenomena happen without witness, there is no reason to invert this order.

Doubtless, but take care; we never know directly the physical phenomena $$B$$ and $$C$$. What we know are sensations $$B'$$ and $$C'$$ produced respectively by $$B$$ and $$C. $$Our consciousness tells us immediately that $$B'$$ precedes $$C'$$ and we suppose that $$B$$ and $$C$$ succeed one another in the same order.

This rule appears in fact very natural, and yet we are often led to depart from it. We hear the sound of the thunder only some seconds after the electric discharge of the cloud. Of two flashes of lightning, the one distant, the other near, can not the first be anterior to the second, even though the sound of the second comes to us before that of tho first?