Refers to two things that form a pair or are considered together. Often used in formal or technical contexts, but can appear in everyday language.
この二つの概念は対偶をなしている。
These two concepts form a pair.
A term in logic referring to the relationship between a conditional statement and its contrapositive. Used in mathematics and philosophy.
ある命題の対偶を考えると、証明しやすくなることがある。
Considering the contrapositive of a proposition can sometimes make it easier to prove.