Reductio ad absurdum

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Reductio ad absurdum is a Latin phrase. It can be translated as reduction to the impossible. Generally, it is also known as Proof by contradiction. In Logic and mathematics it is a method of proving something.

The phrase can be traced back to the Greek η εις άτοπον απαγωγή (hê eis átopon apagogê). This phrase means "reduction to the impossible". It was often used by Aristotle.

The method of proving something works by first stating something is true. Then other things are deduced from that. In the end, there is a contradiction. This contradiction then shows that thing stated first cannot be true.