This article must open with a Warning. In face of the positive information which the sciences supply, the philosophical contribution to this problem will seem disappointingly negative, or at least mine will do so. For I shall insist, and I think we can only rightly insist, that the philosopher is not yet in a position to produce a satisfactory positive theory of the relation between mind and body. And I shall annoy many of you further by insisting that the old-fashioned “dualism” has not really been disproved. However, even if you do not agree with me, it is at any rate a good general piece of advice that, when we are confronted with a philosophical view which has maintained its ground for a very long time but seems to ourselves or to our generation very unreasonable, we should look specially carefully to find the positive grounds which have made so apparently unplausible a doctrine seem true to so many competent thinkers.