more from Keith Devlin

Single Idea 8085

[catalogued under 4. Formal Logic / B. Propositional Logic PL / 1. Propositional Logic]

Full Idea

Where Aristotle had 19 different inference rules (his valid syllogisms), modern propositional logic carries out deductions using just one rule of inference: modus ponens.


'Modus ponens' says if p implies q, and p is true, then q must be true

Gist of Idea

Modern propositional inference replaces Aristotle's 19 syllogisms with modus ponens


Keith Devlin (Goodbye Descartes [1997], Ch. 4)

Book Reference

Devlin,Keith: 'Goodbye Descartes: the end of logic' [Wiley 1997], p.80

A Reaction

At first glance it sounds as if Aristotle's guidelines might be more useful than the modern one, since he tells you something definite and what implies what, where modus ponens just seems to define the word 'implies'.