“The criterion which we use to test the genuineness of apparent statements of fact is the criterion of verifiability.”
Source: Language, Truth, and Logic (1936), p. 16.
Context: The criterion which we use to test the genuineness of apparent statements of fact is the criterion of verifiability. We say that a sentence is factually significant to any given person, if, and only if, he knows how to verify the proposition which it purports to express — that is, if he knows what observations would lead him, under certain conditions, to accept the proposition as being true, or reject it as being false.
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Alfred Jules Ayer 18
English philosopher 1910–1989Related quotes
Source: Jesus or Christianity: A Study in Contrasts (1929), p. 21
Context: Can the use of physical force ever be reconciled with the family spirit?... On one occasion he appears to have resorted to force himself... It sheds no light upon the question as to whether the taking of life, capital punishment, or war are ever justifiable. The criterion by which Jesus judges every method is this; Can it be used appropriately in the home?

Source: Economic Control of Quality of Manufactured Product,1931, p. 18

“Practice is the criterion of truth.”
Mao Zedong, "On Practice" (1937)
Misattributed

Alternate translation: Not one of our mortal gauges is suitable for evaluating non-existence, for making judgments about that which is not a person.
Ни одна наша смертная мерка не годится для суждения о небытии, о том, что не есть человек.
Note-Book of Anton Chekhov (1921)

(1995) Wavelets and Other Phase Space Localization Methods. In: Chatterji, S.D. (ed.). Proceedings of the International Congress of Mathematicians. Birkhäuser, Basel. [10.1007/978-3-0348-9078-6_8]

Source: Criticism and the Growth of Knowledge, 1970, p. 119.

“Only a man's character is the real criterion of worth.”
22 August 1944
My Day (1935–1962)
Source: You Learn by Living: Eleven Keys for a More Fulfilling Life

Simon (1945, p. 179); As cited in: Harry M. Johnson (1966) Sociology: A Systematic Introduction. p. 287.
1940s-1950s

“The criterion of truth is that it works even if nobody is prepared to acknowledge it.”
Source: The Ultimate Foundation of Economic Science (1962), Chapter 5: On Some Popular Errors Concerning the Scope and Method of Economics, § 9 : The Belief in the Omnipotence of Thought