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ON THE NATURE OF THE NOTION OF EXTERNALITY. 219 any other perceptions of events beyond our own brain (and would, like these, inevitably be subject to discontinuity). Now, in the nature of the case, the neurosis underlying any psychosis can never be directly known to the sentient individual ; just because it gives rise to the appropriate phase of consciousness, and not to a perception of itself. 1 Otherwise we should have perceptions ot nothing but changes in the brain. That is to say, all our knowledge of the physical world is based upon our perceptions of that part of it which lies beyond our own brain. Our neuroses are caused by the physical processes connected with these other bodies ; but it is only from our knowledge of these bodies (i.e. the perceived world at large) that we can infer the existence of the neuroses. From which last fact it follows that whatever kind of reality accrues to our neuroses accrues a fortiori to the perceived things which excite them ; but that any attempt to gauge the reality of the latter by means of our knowledge of the former, must involve a fallacy of one kind or another the exact kind of fallacy depending, of course, on the nature of the would-be argument. Hence the futility of attempting as do, for example, Schopenhauer 2 and Professor Karl Pearson 3 to prove that 1 Much in the same way, the hypothetical ether, being the medium of vision, is in its nature incapable of being itself seen. 2 " One must indeed be forsaken by all the Gods, to imagine that the outer perceptible world . . . can have a real objective existence outside us without any agency of our own and that it can then have found its way into our heads through bare sensation and thus have a second existence within us like the one outside " (Fourfold Root of the Principle of Sufficient Reason, chap, iv., sec. 21, in Bonn's Philosophical Library). See also, for an illustration of this idea, Parerga und Paralipomena, vol. ii. sec. 33, p. 49. (seventh ed.) ; and in especial the last two sentences of the first paragraph. " Turn the problem round and ponder over it as we will, beyond the sense-impression, beyond the brain terminals of the sensory nerves we cannot get. Of what is beyond them, of ' tliings-in-themselves ' as the metaphysicians term them, we can know but one characteristic, and this we can only describe as a capacity for producing sense-impressions, for sending messages along the sensory nerves to the brain " (The Grammar of Science, p. 81). See, however, more especially op. cit., chap ii., sec. 11, which is too long for quotation here. Professor Karl Pearson acknowledges, by the way (op. cit., p. 20, footnote), that " it is perhaps impossible to satisfactorily define the metaphysician " ; but he indicates Schopenhauer as a typical member of the tribe. At the same time he says : " the meaning attached by the present writer to the term will become clearer in the sequel " which it certainly does. It almost seems as if, in practice, the Professor employs the name as a term of contempt for all who do not share, down to their last details, his own (happily in some respects original) metaphysical views.