more on this theme | more from this thinker | more from this text
Full Idea
Frege's algorithm of identity is the law of putting equals for equals.
Gist of Idea
Frege's algorithm of identity is the law of putting equals for equals
Source
report of Gottlob Frege (Grundlagen der Arithmetik (Foundations) [1884]) by Willard Quine - Identity, Ostension, and Hypostasis 4
Book Ref
Quine,Willard: 'From a Logical Point of View' [Harper and Row 1963], p.76
A Reaction
Quine, and most modern philosophers, seem to accept universal substitutivity as a sufficient condition for identity. But you then get the problem of coextensionality (renate/cordate), which can only be solved by introducing modality.