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 198. B. RUSSELL : that it involves an assertion as to the connexion of past and future which may or may not be true, and which elsewhere Leibniz explicitly denies. All equations are logical equations, i.e., they state mutual implications ; hence if any phenomena can be found to satisfy the equation "cause = effect," there must be events at different times so related that each implies the other. Hence the effect is on the same logical level as the cause, and the past has no logical priority over the future. Leibniz holds, however, that the past is prior in nature to the future (e.g. G-erh., iii., 582) ; and M Couturat has shown that this opinion is a vital part of his system (Couturat, p. 222). But Leibniz had not a sufficient knowledge as to the nature of logical priority, or as to the con- nexion of Symbolic Logic with Mathematics, to have understood the inconsistency into which he was led on this point. Dr. Gassirer holds (p. 331) that it was for the sake of the principle of conservation that Leibniz denied the interaction of soul and body. In view of the texts in the letters to Arnauld and in M. Couturat's work, this view appears to me no longer tenable : the logical argument is short, clear, and on its own premisses valid. I see therefore no reason to require any other ground for Leibniz's opinion. Part iii., on Leibniz's Metaphysics, endeavours to show that his views were practically those of Kant, and that they were derived largely from his scientific studies, especially from Dynamics. Both these opinions appear to me to be erroneous. In rejecting the latter, I agree wholly with M. Couturat ; l and as he has new documentary evidence, his position may, I think, be regarded as established. The question as to the interpretation of Leibniz's metaphysics is more difficult. Dr. Cassirer regards the passages in the letters to Arnauld as treating the relation of the Ego to its states as analogous to that of subject and predicate (p. 358). For my part, I cannot discover any justification for seeing a mere analogy where absolute identity appears to be plainly asserted. The positing of identity, says our author, is only understood by reduction to the conception of the Ego (p. 360). The passage in Gerh., ii., p. 43, appears to me to show quite conclusively that the reduction is the other way. I confess that a subjective view of identity is to me unintelligible. Identity, Dr. Cassirer says (p. 131), is not found by thought, but created in the progress of know- ledge. This means that there is no identity until we think so. Nature presents me with Jones, and I, wishing to see my old friend Smith, postulate that it is Smith ; and thereupon, as by magic, the thing is done. But what it was I wished, seeing that before my wish the identical Smith had no kind of being, it seems totally impossible to conceive. The whole view, in short, confounds the process of learning with the facts learned, and is unable to conceive propositions except as mental existents. And it seems a sufficient 1 See the end of the review of M. Couturat, supra.