ON THE NATUEE OF THE NOTION OF EXTEENALITY. 223 Green and his following) lies in his identification of the externality of the material world with its spatiality. But it will now, I think, be clear that, though undoubtedly space and time are the framework (whether or not a priori) on which the whole of our knowledge of the material world is constructed, in order to this end we require, in addition, the, principle of externality as above defined. III. It now only remains for us to estimate the immediate metaphysical significance of our results. This part of our task, however, need not detain us long, since the foregoing analysis of the notion of externality was necessitated pre- cisely by the fact that idealists of all denominations have invariably missed its true nature ; so that all their arguments against its validity fall beside the mark. One of the most essential conditions of thought is that any predication only attains significance in so far as the idea which the predicate-term expresses is opposed to some other idea. This is implied in the meaning of the word "significant " itself. If, therefore, the word "mind" or " consciousness " is to have any meaning for us (any meaning, that is, more definite than that of " something-or-other ") it must be as contrasted with something that is not consciousness. The only thing that can be so contrasted with mind is matter. Now the idea of matter has been shown to presuppose the notion of externality, and the essence of the notion of externality has been shown to lie in the idea of existence which is independent of consciousness. Therefore the word " mind " is as much dependent for its meaning on the idea of unperceived existence as is the word "matter" itself. All which may be more briefly stated by saying that the dis- tinction between consciousness and the external world is also a distinction between the external world and consciousness. To subsume the idea of matter under that of mind would be to empty the word "mind " of all meaning. Thus the idealistic account of Nature, whether in the form of esse is percipi or esse is intelligi, is essentially self-contradictory, that is, meaningless ; and, consequently, the question whether it is true or false is also devoid of meaning. Nor is this charge a merely formal one. The question whether the external world exists, if intended as an inquiry into the constitution of the universe, is meaningless simply because any question concerning the
