Full Idea
Since every definition is an equation, one cannot define equality itself.
Gist of Idea
Since every definition is an equation, one cannot define equality itself
Source
Gottlob Frege (Review of Husserl's 'Phil of Arithmetic' [1894], p.327)
Book Reference
-: 'Mind July 1972' [-], p.327
A Reaction
This seems a particularly nice instance of the general rule that 'you have to start somewhere'. It is a nice test case for the nature of meaning to ask 'what do you understand when you understand equality?', given that you can't define it.
Related Idea
Idea 16498 Identity cannot be defined, because definitions are identities [Wiggins]