Gottlob Frege Quotes
Attributed in "Mathematics as grammar: 'Grammar' in Wittgenstein's philosophy of mathematics during the Middle Period" by A. A. B. Aspeitia, Indiana University, (p. 25), 2000.
"The thought: A logical inquiry" by Gottlob Frege in "Readings in the Philosophy of Language" edited by Peter Ludlow, (p. 27), 1997.
Gottlob Frege (1952). “Translations from the Philosophical Writings of Gottlob Frege”
Gottlob Frege (1952). “Translations from the Philosophical Writings of Gottlob Frege”
Note in the appendix of "Grundlagen der Arithmetik" (Vol. 2), after Frege had received a letter of Bertrand Russell in which Russell had explained his discovery of, what is now known as, Russell's paradox, 1903.
Gottlob Frege, J. L. Austin (1980). “The Foundations of Arithmetic: A Logico-Mathematical Enquiry Into the Concept of Number”, p.4, Northwestern University Press
"From Frege to Godel: A Source Book in Mathematical Logic, 1879-1931". Book edited by J. van Heijenoort, "Letter to Bertrand Russel" (1902), 1967.