Quote by Frege, Gottlob
"The reference of a term cannot be determined by introspection alone."
More from Frege, Gottlob
"A thought is a proposition which we apprehend."
"The word 'number' is surely not without a sense; but when we have the sentence 'the number of roots of this equation is four', it seems very difficult to give the meaning of the word 'number' here."
"Functions are concepts; concepts are functions."
"The content of a thought may have different kinds of parts."