noun
reductio ad absurdum; proof by contradiction
A logical method in mathematics and philosophy where a proposition is proven by showing that its negation leads to a contradiction.
背理法を使って、√2が無理数であることを証明できる。
Using proof by contradiction, one can prove that √2 is irrational.
Proof by contrapositive, a related but distinct logical method.
From 背理 (contradiction) + 法 (method). The term is a direct translation of the Latin 'reductio ad absurdum'.