"The civilized man has a moral obligation to be skeptical. . . . Any man who for one moment abandons or suspends the questioning spirit has for that moment betrayed humanity."

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The principles of logic and mathematics are true simply because we never allow them to be anything else. And the reason for this is that we cannot abandon them without contradicting ourselves, without sinning against the rules which govern the use of language, and so making our utterances self-stultifying. In other words, the truths of logic and mathematics are analytic propositions or tautologies.

— A.J. Ayer