invalidity

Invalidity is the state of being invalid or not having validity. The term is used in several distinct but related senses, including legal, logical, and historical or social usage.

In law, invalidity refers to a lack of legal effect or enforceability. An act, contract, or statute may be void or voidable. A void act has no legal effect from the outset, while a voidable act is initially valid but can be rescinded or annulled by one of the parties or a competent authority. Common grounds for invalidity include absence of consent, lack of capacity, misrepresentation, duress, illegality, or mistake. Remedies for invalidity typically involve recission, reformation, or judicial declaration that the act is void.

In logic and argumentation, invalidity describes a failure of an argument to guarantee its conclusion. An argument is valid if the conclusion follows logically from the premises; it is invalid if that logical connection does not hold, even when the premises may be true. Validity is a structural property of the argument, independent of the actual truth of the premises. A sound argument is both valid and with true premises.

Historically and in social language, invalidity has referred to disability or chronic illness. The noun “invalid” for a person is now considered outdated or insensitive in contemporary usage, with preferred terms such as “person with a disability.” In some contexts, “invalidity” appears in phrases like invalidity benefits or pension, relating to disability status for social support.