Speech act theory proposes that language is used not just to convey information but also to perform actions. A speech act is the basic unit of human communication. John Austin first proposed speech act theory, noting that language is used to do things as well as assert things. Speech acts have propositional meaning from the literal words, illocutionary meaning from the social function, and perlocutionary meaning from the effect on the listener. Speech acts can be classified into assertives, directives, commissives, expressives, and declarations.