Speranza
Grice speaks of 'predicate calculus with identity' in "Reply to Richards". In such a calculus, alla Russell, 'identity', symbolised by " = " becomes DEFINED in terms of Leibniz's law.
Wikipedia should have the complete definition!
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I don't think that's really correct.
ReplyDeleteLiebniz's law insists on their being a substantive (not sure that's the right word) difference between distinct individuals, whereas the identity in the predicate calculus only satisfies a trivialised version of leibniz's law.
Any two distinct individuals a and b differ in that a=a but not b=a, and in the first order predicate calculus that (and its logical consequences) might be the only difference between two distinct individuals, which would not be enough for Leibniz.
RBJ