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."

"A concept is a function whose value is always a truth-value."

"Language is not everything. It is only an instrument for communicating thoughts."

"We cannot avoid thoughts; they come to us."

"The sense of a proper name is the mode of presentation of what it stands for."

"One should distinguish between the sense and the reference of a sign."

"Meaning is not in the mind; it is in the world."

"A thought is true or false; there is no third option."

"Numbers are objects of thought, not creations of the mind."

"The question 'What is a number?' deserves a serious answer."

"Logic is the science of the laws of truth."

"Abstraction is necessary for understanding."

"We must be rigorous in our thinking."

"The mind cannot invent truths; it can only discover them."

"Every object has a determinate nature."

"Sense determines reference."

"A name without sense is meaningless."

"The law of contradiction is fundamental."

"We speak of truth and falsehood only of thoughts."

"Mathematical truth is objective and necessary."

"Concepts are not ideas in the psychological sense."

"Logic governs all thinking."

"The pursuit of truth is the highest calling."

"Words have senses and references."

"One cannot think without using concepts."

"Identity is a fundamental relation."

"Mathematics rests on logic alone."