Illocutionary act is a term in linguistics introduced by John L. Austin in investigation of the multiple meanings in a speech act. The simplified gist of Austin's theory is that if you utter "Is there any salt?" at the dinner table the illocutionary force is that you desire salt, as distinct from the locutionary act (a question about the presence of salt) and the perlocutionary act (causing somebody to hand you the salt).

Searle extended and refined Austin’s work on illocutionary acts. He observed that Austin’s decomposition of speech acts into illocutionary force propositional

content shows up in the different kinds of negation that can be performed in a sentence.

In conclusion, we believe that speech acts are a good link between the mental states agents and purposeful communication. While a comprehensive theory of speech acts will strain most contemporary theories of rational agency, requiring a very expressive theory of action and mental state, it also provides a good testbed for a theory of agency in a multi-agent world. While many of the specific concerns of natural language speech act work, such as the interpretation of ambiguous utterances, may be alleviated by using more restricted agent communication languages,many of the same issues will arise for cooperative systems that must infer intentions others.