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Published online by Cambridge University Press: 01 January 2020
The Principle of the Identity of Indiscernibles (PH), commonly attributed to Leibniz, has given rise to much discussion and debate. Thus philosophers have argued over how it should be formulated, whether it is (necessarily) true, and what, if any, metaphysical consequences it has.
It is not my intention to add to these discussions here, having done so elsewhere. Rather, I intend to introduce and defend a closely related principle which I shall, for want of a better name, refer to as The Principle of the Identity of Necessary Similarity’ (PINS).
In section II, I briefly recapitulate some of the distinctions and other relevant points which are customarily made in connection with (PH). This is all too familiar material, but it is necessary in order to provide a general framework of concepts in terms of which we can discuss (PINS) in an intelligible fashion.
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13 This is known as ‘Brouwer’s axiom.’ See Hughes & Cresswell, 57, where this axiom is briefly explained.
14 Thus Kripke says that necessary identity is a ‘self-evident [thesis] of philosophical logic independent of natural language’ (4).
15 I would like to thank my former teacher, Prof. Romane Clark, and anonymous referees of this journal for many helpful comments and suggestions.
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