Journal of the History of Philosophy

Notes and Discussions WHAT IS THE GROUND FOR THE PRINCIPLE OF THE IDENTITY OF INDISCERNIBLES IN LEIBNIZ'S CORRESPONDENCE WITH CLARKE? It has been generally recognized in the literature that the basis for the Identity of Indiscernibles in the correspondence with Clarke (1715) is the Principle of Sulficient Reason, "and this principle generally gives contingent results.''1 It would seem that this conclusion runs directly counter to Leibniz's views expressed in other places, and there are a number of different approaches that commentators have traditionally taken to this apparent inconsistency. Russell, for example, simply refuses to take Leibniz seriously here: "The above argument for his principle is far from cogent as it stands, and does not adequately represent his meaning. ''2 I would like to argue that Leibniz's position in this correspondence is a cogent one. One can never know for certain, of course, whether any position ever "adequately represents" the meaning (i.e. intentions) of an author, but the plausibility of doubts of this kind is diminished if it can be shown that the position in question is a cogent one, and even more reduced if it can be shown how the position fits into a general strategy of the author. I will deal with the second point first. I suspect that Leibniz is presenting an argument couched in cotmterfaetual terms (i.e. "Even if -- were the case, [and it isn't] . . .), This suggestion seems to be supported by the opening lines of L III, 5: ~ I have many demonstrations to confute the fancy of those who take space to be a substance, or at least an absolute being. But I shall only use, at the present, one demonstration , which the author here gives me occasion to insist upon. I say, then, that if space were an absolute being, there would happen something, for which it would be impossible that there should be a sufficient reason.4 Leibniz should thus not be taken as asserting categorically that space and time could be absolute, rather he is here presenting a certain argument which he takes to be valid, but not sound. There are, however, other places5 where Leibniz cerx H. G. Alexander, The Leibniz-Clarke Correspondence (Manchester, 1956). This correspondence appears in C. J. Gerhardt, Die Philosophischen Schriften von Gott/ried Wilhelm Leibniz (Hildesheim: Georg Olms, 1961; reprinted from the first edition of 1890), VII, 347-440. Here, Leibniz's letters are in the original French; my quotations are ther6fore from Alexander. z B. Russell, A Critical Exposition o/the Philosophy of Leibniz (London: Allen & Unwin, 1951), p. 56. 3 I shall refer to passages in the text by letter and paragraph number: e.g. "L IlI, 5" refers to the fifth paragraph of Leibniz's third letter. 4 Gerhardt, 363-364; Alexander, p. 26. The boldface emphasis is mine. E.g. L V, 21, Gerhardt, 393-394, Alexander, p. 61; L V, 25, Gerhardt 394-395, Alexander , p. 62; L V, 28, Gerhardt, 395; Alexander, p. 63. [95] 96 HISTORY OF PHILOSOPHY taiuly seems to be categorically asserting the logical possibility of absolute space and time. I would therefore hesitate to consider the question of inconsistency entirely disposed of in the manner just suggested. I do not intend to try to resolve the problem, rather I intend to try to expose the nature of Leibniz's argument, an argument which, I think, can be seen to be cogent. Before I do that, however, I should like to make a few observations about what certain commentators have had to say about the general problem of the modality of the Principle of the Identity of Indiscernibles in a Leibnizian system. Nicholas Rescher is decisive in rejecting the suggestion that Leibniz might actually be committed to a contingent Principle of the Identity of Indiscernibles. If there were two distinct indiscernibles a and b, then there would have to be present in the complete individual notion of substance a truth regarding it--namely, that there are several other substances answering exactly to its own description--which could not reasonably be held to be something programmed into the concept of a, since b is conceptually indistinguishable from a. The principle should thus be...