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HEN we are trying to think clearly we are wont to be disturbed if our friends accuse us of wandering from the sure grounds of science and entering the jungle of metaphysics.

Nevertheless, it must be acknowledged that, without realizing it, all men do really devote a fair proportion of their thought to problems which, strictly speaking, are of a metaphysical nature: and the question as to the relation of 'mind to body' which has an entrancing interest for so large a body of thoughtful people, is clearly one in reference to which no one can take a definite position without at the same time assuming an attitude in relation to fundamental metaphysical principles.

We turn to the skilled biologist in these days for expert opinion in this matter, only to find him tarred with the same brush; for as a biologist the problem before him has properly no significance. As a biologist he is concerned with forms of 'animal behavior,' to use Lloyd Morgan's happy phrase. If he takes into consideration in any way the consciousness of animals, in that fact he assumes the attitude of the metaphysician. It is clearly because he takes this step into the metaphysical domain, without realizing it, that we find among those psychological biologists who consider the consciousness of animals so wide a divergence of opinion as to the conditions under which such consciousness exists.

But, as I have said, this matter is of great interest to all of us, and is looked upon as deserving our serious consideration. It is quite worth our while then to acknowledge frankly that we are dealing with a metaphysical problem, and at the start to make a rather deep plunge, laying aside for the moment all thought of the consciousness of animals, and asking ourselves what ground we have for our every-day assumption that other men are conscious as we ourselves are.

The ready answer seems to be that they tell us of their conscious states. But evidently this reply does not suffice us, for it becomes very clear upon consideration that no amount of hearsay evidence would serve to convince us of the fact that these other men are conscious did we not note that our activities, which are very like their activities, are accompanied in our experience by modifications in our