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of past conscious experience recalled in memory: and the implied classification may obviously be erroneous either through inaccuracy of memory or a mistake in the comparative judgment. And the risk of error cannot well be avoided by eliminating along with inference this implicit classification: for the psychical fact observed cannot be distinctly thought at all without it: if we rigorously purge it away, there will be nothing left save the cognition of self and of we cannot say what psychical fact. Nay it is doubtful whether even this much will be left for the Empiricist’s observation: since he may share Hume’s inability to find a self in the stream of psychical experience, or to maintain a clear distinction between psychical and material fact. Thus the Empiricist criterion, if extended to purge away comparison as well as inference, may leave us nothing free from error but the bare affirmation of Fact not further definable.

Here again I am far from denying the value of the Empirical criterion. I have no doubt of the importance of distinguishing the inferential element in our apparently immediate judgments as far as we can, with a view to the elimination of error. Only the assertion that we can by this procedure obtain a residuum of certainly true cognition seems to me neither self-evident nor confirmed by experience.

I pass to examine the criterion propounded by Mr. Herbert Spencer in his Principles of Psychology (part vii., ch. ix.-xii.): which, in his view is applicable equally to particular and universal cognitions. It is there laid down that “the inconceivableness of its negation is that which shows a cognition to possess the highest rank—is the criterion by which its unsurpassable validity is known”. . . . “If the negation of a proposition is inconceivable”—i.e., “if its terms cannot by any effort be brought before consciousness in that relation which the proposition asserts between them”—we “have the highest possible logical justification for holding it to be unquestionable.” This is, in Mr. Spencer’s view, the Universal Postulate, on the validity of which the validity of all reasoning depends.

Before we examine the validity of the criterion, the meaning of the term “inconceivable” requires some discussion. In replying to a criticism by J. S. Mill, Mr. Spencer—while recognising that “inconceivable” is sometimes loosely used in the sense of “incredible”—repudiates this meaning for his own use. But I agree with Mill in regarding this repudiation as hasty, so far as the criterion is applied to propositions that represent particular facts—