Abstract: An account of the speech act of assertion is proposed. Three technical notions—proposition, propositional concept, and speaker presupposition are defined and used to characterize the effect of an assertion on the context. Some constraints on the appropriateness of assertion are proposed and used to resolve some puzzles about identity statements and negative existential statements using proper names.

Keywords: assertion, identity, proper name, proposition, propositional concept, speaker presupposition, speech act,