ástæðu

ásæðu is an Icelandic noun meaning reason, cause, or justification. It denotes the basis or motivation for a belief, action, statement, or decision. In everyday usage people refer to reasons for doing something; in formal contexts such as philosophy, rhetoric, or law, the term is used to articulate a justification or rationale behind a proposition or policy.

The concept covers both factual causes and normative justifications. For example, one might discuss the basis for passing a law or for changing an opinion. In Icelandic scholarship, distinctions are sometimes drawn between physical causation (orsök) and justificatory grounds (ástæða). The term is common across historical and contemporary Icelandic writing, and remains a standard way to describe why something is the case.

Related terms include orsök (cause) and rök (reason or argument). The word is native to Icelandic and is part of a family of words for justification in Nordic languages, with equivalents in Norwegian and Danish meaning "cause" or "reason."