The signs of science are, some certain and infallible; some, uncertain. Certain, when he that pretendeth the science of anything, can teach the same; that is to say, demonstrate the truth thereof perspicuously to another; uncertain, when only some particular events answer to his pretence, and upon many occasions prove so as he says they must.

Leviathan, Or, The Matter, Form, and Power of a Commonwealth, Ecclesiastical and Civil (2nd edition), Chapter V (p. 30)