### Single Idea 9402

#### [catalogued under 4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / c. Derivation rules of PL]

Full Idea

Reduction ad Absurdum (RAA): Given a proof of B∧¬B from A as assumption, we may derive ¬A as conclusion, depending on the remaining assumptions (if any).

Clarification

¬ is 'not'

Gist of Idea

RAA: If assuming A will prove B∧¬B, then derive ¬A

Source

E.J. Lemmon (Beginning Logic [1965], 1.5)

Book Reference

Lemmon,E.J.: 'Beginning Logic' [Nelson 1979], p.40