Single Idea 9842

[catalogued under 9. Objects / F. Identity among Objects / 2. Defining Identity]

Full Idea

In his middle period Frege rated identity indefinable, on the ground that every definition must take the form of an identity-statement. Frege introduced the notion of criterion of identity, which has been widely used by analytical philosophers.

Clarification

His middle period is 1891-1906

Gist of Idea

Frege introduced criteria for identity, but thought defining identity was circular

Source

Michael Dummett (Frege philosophy of mathematics [1991], Ch.10)

Book Reference

Dummett,Michael: 'Frege: philosophy of mathematics' [Duckworth 1991], p.113


A Reaction

The objection that attempts to define identity would be circular sounds quite plausible. It sounds right to seek a criterion for type-identity (in shared properties or predicates), but token-identity looks too fundamental to give clear criteria.