A proof in which you assume temporarily that the conclusion is not true, and then deduce a contradcition.

a proof in which one false assumption is made

A proof that begins by assuming the denial of what is to be proved and then deducing a contradiction from this assumption.

The method of proof that assumes the negation of what is to be proved and deduces a contradiction.

A deductive proof using contradiction or elimination to rule out all except the desired conclusion.

A proof which assumes that the desired conclusion is not true and shows that this assumption leads to a contradiction.