Reductio ad absurdum - Salmon

(Originally written September 6, 2005 in Book 1)

Logic

Wesley C. Salmon

1963

Reductio ad absurdum

-Reductio ad absurdum is a valid argument form that is widely used

-Sometimes it is used to establish a positive conclusion, but often it is used to refute the thesis of an opponent

Form:

To prove p, assume not-p

Deduce a false statement either: p (which contradicts the assumption not-p) or q and not-q (a self contradiction) or some other statement r, which is known to be false

-reductio ad absurdum is closely related to denying the consequent

-reductio ad absurdum is frequently used in mathematics

-Plato uses reductio ad absurdum in his dialogues

Examples: