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 make one the subordinate and adjective of the other. And I will begin by making some remarks on the parallel series. But I must ignore the historical development of this view, and must treat it barely as if it were an idea which is offered us to-day.

I would observe, first, that an assertion or a denial of causation can hardly be proved if you insist on demonstration. You may show that every detail we know points towards one result, and that we can find no special reason for taking this result as false. And, having done so much, you certainly have proved your conclusion. But, even after this, a doubt remains with regard to what is possible. And, unless all other possibilities can be disposed of, you have failed to demonstrate. In the particular doctrine before us we have, I think, a case in point. The mere coincidence of soul and body cannot be shown to be impossible; but this bare possibility is, on the other hand, no good reason for supposing the coincidence to be fact.

Appearance points to a causal connection between the physical and psychical series. And yet this appearance might possibly be a show, produced in the following way. There might on each side be other conditions, escaping our view, which would be enough to account for the changes in each series. And we may even carry our supposition a step further on. There might on both sides be, within each series, no causal connection between its events. A play of unknown conditions might, on either side, present the appearance of a series. The successive facts would in that case show a regular sequence, but they would not actually be members and links of any one connected series. I do not see how such a suggestion can be proved to be impossible; but that is surely no reason for regarding it as fact. And to this same result we are led, when we return to consider the idea of two coinciding series. The