more from Bertrand Russell

Single Idea 5395

[catalogued under 5. Theory of Logic / B. Logical Consequence / 5. Modus Ponens]

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'.

Gist of Idea

Demonstration always relies on the rule that anything implied by a truth is true

Source

Bertrand Russell (Problems of Philosophy [1912], Ch. 7)

Book Reference

Russell,Bertrand: 'The Problems of Philosophy' [OUP 1995], p.40


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.