Richard Feynman Quote
We find that the statements of science are not of what is true and what is not true, but statements of what is known with different degrees of certainty: "It is very much more likely that so and so is true than that it is not true".
The Pleasure of Finding Things Out: The Best Short Works of Richard P. Feynman (ed. Basic Books, 2005) - ISBN: 9780465023950