 The figures and modes of speech are common, socially useful practices. They perpetuate themselves through precedent following, social acceptance, individual habit and association, and traditional transmission from one generation of speakers to another. Precedent operates when hearers call on their knowledge of the forms speakers commonly use to either interpret speakers in new contexts, or to predict what hearers will understand. The forms are less arbitrary than lexical or syntactic conventions, but no one has to implicate rather than say things, or use one form of implicature rather than others.