Full Idea
A Fregean concept is a function that assigns to each object a truth value. So instead of the colour green, the concept GREEN assigns truth to each green thing, but falsity to anything else.
Gist of Idea
The Fregean concept of GREEN is a function assigning true to green things, and false to the rest
Source
William D. Hart (The Evolution of Logic [2010], 2)
Book Reference
Hart,W.D.: 'The Evolution of Logic' [CUP 2010], p.47
A Reaction
This would seem to immediately hit the renate/cordate problem, if there was a world in which all and only the green things happened to be square. How could Frege then distinguish the green from the square? Compare Idea 8245.
Related Idea
Idea 8245 The logical attitude tries to turn concepts into functions, when they are really forms or forces [Deleuze/Guattari]