Implicature as applied to speakers is the act of meaning that one thing is the case by saying that something else is. It is an indirect speech act closely related to implying. Semantic implicatures are determined by the meaning of the sentence used, whereas conversational implicatures depend on the context of utterance. General forms of implicature, used frequently with a wide variety of sentences and languages, include figures of speech (irony, hyperbole, meiosis, litotes, metonymy, synecdoche, metaphor) and modes of speech (relevance, strengthening, limiting, and metalinguistic implicature, damning with faint praise, and loose use). These forms are conventional ways of using and understanding speech, essential for fully understanding speakers, and acquired at an early age along with lexical and semantic conventions. A sentence has an implicature when speakers conventionally use sentences of that form with the corresponding implicature. In addition to the semantic implicatures, sentences have a variety of generalized conversational implicatures, including some limiting implicatures, strengthening implicatures, ignorance implicatures, common metaphors, and embedded implicatures. Implicatures become idioms when they cease to be indirect. There are many reasons why speakers implicate things. Some also apply to saying (communication, self-expression, record creation) while some distinguish implicating from saying (verbal efficiency, misleading without lying, veiling, good social relations, style, and entertainment). A sentence has an implicature today because that use became self-perpetuating and was picked up by today’s speakers from previous speakers. Traditional pragmatic theories maintain that conversational implicatures can be derived from various principles governing conversation, but the dependence of implicature on intention and convention, and the variety of conflicting goals implicature serves, make such derivations unsound and invalid. Like understanding sentences, interpreting implicatures is largely the automatic exercise of a competence acquired with one’s native language rather than derivation from general principles.