In linguistics and philosophy of language, an utterance is felicitous if it is pragmatically well-formed. An utterance can be infelicitous because it is self-contradictory, trivial, irrelevant, or because it is somehow inappropriate for the context of utterance. Researchers in semantics and pragmatics use felicity judgments much as syntacticians use grammaticality judgments. An infelicitous sentence is marked with the pound sign.
The terms felicitous and infelicitous were first proposed by J. L. Austin as part of his theory of speech acts. In his thinking, a performative utterance is neither true nor false, but can instead be deemed felicitous or infelicitous according to a set of conditions whose interpretation differs depending on whether the utterance in question is a declaration ("I sentence you to death"), a request ("I ask that you stop doing that") or a warning ("I warn you not to jump off the roof").