Speech Act Theory, in Linguistics, describes how language can be used to do things, rather than merely comment on the state of the world. Typically when we think of an utterance, it is usually either merely stating a fact, (Today is the first day of spring), asking a question, (How many angels can dance on the head of a pin?), or acting as some sort of a command: (Don't be afraid). All of these sentences, while having the potential to effect change in the world, do not actually contain the power to do anything on their own. In contrast, Speech Act Theory describes sentences whose very utterance causes things to occur. For instance, the phrase, "I pronounce thee man and wife" is what actually causes the union to occur. The couple is not married until the official says so.

More examples of such phrases are:

In each of these cases, it is the act of saying the phrase that is important; it is only by declaring a man a knight that he becomes knighted. We see here the performative function of language. Such performative acts do not have to be as direct as the examples, in fact much of our language is rather oblique. Take for example a guest who is very hot, but does not want to disturb the host. She might make the statement, "Wow, it's really hot in here," with the intention that the host would understand her discomfort and open the window. This phrasing of the request allows for politeness, and might be more socially acceptable than out and out asking.

For more information, see also:
Performative Linguistics
Illocutionary Force
Perlocutionary Force


Speech act theory was developed by J.L. Austin and John Searle in the 1960's. Essential to the theory is the idea that certain felicity conditions must be met in order for the utterance to have any effect. Not just anybody can name a ship or marry a couple. A speech act is not valid unless the following are fulfilled:

It is because of these conditions that actors aren't really married when they make a movie (inappropriate authority and circumstance), an insane person cannot make promises (sincerity?) and a bet is not made unless both parties agree (completeness).