more from E.J. Lemmon

### Single Idea 9531

#### [catalogued under 4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / b. Terminology of PL]

Full Idea

If A and B are expressible in propositional calculus notation, they are 'contrary' if they are never both true, which may be tested by the truth-table for ¬(A∧B), which is a tautology if they are contrary.

Gist of Idea

'Contrary' propositions are never both true, so that ¬(A∧B) is a tautology

Source

E.J. Lemmon (Beginning Logic [1965], 2.3)

Book Reference

Lemmon,E.J.: 'Beginning Logic' [Nelson 1979], p.69