Full Idea
Geach rejects the standard formulation of Leibniz's Law as incomplete, since it includes a non-relativized identity predicate.
Gist of Idea
Leibniz's Law is incomplete, since it includes a non-relativized identity predicate
Source
report of Peter Geach (Reference and Generality (3rd ed) [1980]) by Ryan Wasserman - Material Constitution 6
Book Reference
'Stanford Online Encyclopaedia of Philosophy', ed/tr. Stanford University [plato.stanford.edu], p.16
A Reaction
Not many people accept Geach's premiss that identity is a relative matter. I agree with Wiggins on this, that identity is an absolute (and possibly indefinable). The problem with the Law is what you mean by a 'property'.