Reductio ad Absurdum

From Logic

Reductio ad absurdum (Latin for reduction to the absurd) also known as proof by contradiction, is a type of logical argument where one assumes a claim for the sake of argument, derives an absurd or ridiculous outcome, and then concludes that the original assumption must have been wrong as it led to an absurd result. It makes use of the Law of Non Contradiction - a statement cannot be both true and false. In some cases it may also make use of the Law of the Excluded Middle - a statement must be either true or false. The first documented uses of the argument are found in the writings of Aristotle.

In Formal Logic, reductio ad absurdum is used when a formal contradiction can be derived from a premise, allowing one to conclude that the premise is false. If a contradiction is derived from a set of premises, this shows that at least one of the premises is false, but other means must be used to determine which one.

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