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Ideas for 'That Politics may be reduced to a Science', 'Problems of Philosophy' and 'Introduction to Philosophical Papers I'

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5. Theory of Logic / B. Logical Consequence / 5. Modus Ponens

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.