itself, or produce motion, is incomprehensible and unprecedented. The Will also is known by its effects and not by its essence. I know it as the cause of motion; but to conceive matter producing motion, would be evidently to conceive an effect without a cause, or rather not to conceive anything at all.
It is no more possible for me to conceive how the will moves the body, than how the sensations affect the soul. I even know not why one of these mysteries ever appeared more explicable than the other. For my own part, whether at the time I am active or passive, the means of union between the two substances appear to me absolutely incomprehensible. Is it not strange that the philosophers have thrown off this incomprehensibility, merely to confound the two substances together, as if operations so different could be better explained as the effects of one subject than of two.
The principle which I have here laid down, is undoubtedly something obscure; it is however intelligible, and contains nothing repugnant to reason or observation. Can we say as much of the doctrines of materialism? It is very certain that, if motion be essential to matter, it would be inseparable from it; it would be always the same in every portion of it, incommunicable, and incapable of increase or diminution; it would be impossible for us even to conceive matter at rest. Again, when I am told that motion is not indeed essential to matter, but necessary to its existence, I see through the attempt to impose on me by a form of words, which it would be more easy to refute, if more intelligible. For, whether the motion of matter arises from itself, and is therefore essential
