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5395 | Demonstration always relies on the rule that anything implied by a truth is true [Russell] |
Full Idea: All demonstrations involve the principle that 'anything implied by a true proposition is true', or 'whatever follows from a true proposition is true'. | |
From: Bertrand Russell (Problems of Philosophy [1912], Ch. 7) | |
A reaction: This is modus ponens, a broad principle of rationality, rather than of strict logicality, because it covers practical inferences and vague propositions. Presumably truth is a prior concept to implication, and therefore more metaphysically basic. |