'Facts, facts, facts,' cries the scientist if he wants to emphasize the necessity of a firm foundation for science. What is a fact? A fact is a thought that is true. But the scientist will surely not recognize something which depends on men's varying states of mind to be the firm foundation of science.
"The thought: A logical inquiry" by Gottlob Frege in "Readings in the Philosophy of Language" edited by Peter Ludlow, (p. 27), 1997.
