“Theories are only verified hypotheses, verified by more or less numerous facts. Those verified by the most facts are the best, but even then they are never final, never to be absolutely believed.”
Introduction à l'Étude de la Médecine Expérimentale (1865)
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Claude Bernard 21
French physiologist 1813–1878Related quotes

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.
“I ask you to believe nothing that you cannot verify for yourself.”
All and Everything: Views from the Real World (1973)

Patheos, The Cow http://www.patheos.com/blogs/reasonadvocates/2016/01/22/the-cow/ (January 22, 2016)