Assertions

An assertion is a statement presented as true. In ordinary usage, it is a claim that something is the case. In logic and mathematics, an assertion is a declarative sentence that can be assigned a truth value—true or false. The set of all affirmed propositions forms the basis of a theory; axioms and theorems are types of assertions. A proof shows that a given assertion follows from prior assertions under established rules.

In philosophy and linguistics, an assertion is an act of asserting something: a speech act in which the speaker commits to the truth of a proposition and presents it as knowledge or belief. It can carry epistemic or evidential commitments and may be contrasted with questions, commands, or other illocutionary acts.

In computer science, an assertion is a statement embedded in code that is intended to be checked at run time. It expresses a condition that must hold at that point in execution. If the condition fails, an assertion typically triggers an error or exception, helping to detect bugs or enforce invariants. Assertions can be enabled or disabled in different environments and are commonly used as debugging aids during development.

The term is sometimes used more loosely to refer to claims made without independent evidence, or to bold statements in arguments. Across disciplines, an assertion denotes a stated claim presented as true and, in many contexts, subject to verification.