Full Idea
A thought is not something subjective, is not the product of any form of mental activity; for the thought that we have in Pythagoras's theorem is the same for everybody.
Gist of Idea
Thoughts are not subjective or psychological, because some thoughts are the same for us all
Source
Gottlob Frege (Logic in Mathematics [1914], p.206)
Book Reference
Frege,Gottlob: 'Posthumous Writings', ed/tr. Hermes/Long/White etc [Blackwell 1979], p.206
A Reaction
When such thoughts are treated as if the have objective (platonic) existence, I become bewildered. I take a thought (or proposition) to be entirely psychological, but that doesn't stop two people from having the same thought.