Speech act theory is proposed by J. L. Austin and has been developed by J. R. Searle. Basically, they believe that language is not only used to inform or describe things, it is often used to “do things”, and to perform acts.

Austin suggests three basic senses in which in saying something one is doing something and three kinds of acts are performed simultaneously.

The first sense is an ordinary one. When we speak we move our vocal organs and produce a number of sounds, organized in a certain way and with a certain meaning. In this sense, when somebody says “Morning!”, we can ask a question like “What did he do?” instead of “What did he say?” And the answer could be that he produced a sound, word or sentence-“Morning!” The act performed in this sense is called a locutionary act. And when we speak, we not only produce some units of language with certain meanings, but also make clear our purpose in producing them, the way we intend them to be understood, or they also have certain forces as Austin prefers to say. In the example of “Morning!” we can say it has the force of a greeting, or it ought to have been taken as a greeting. This is the second sense in which to say something is to do something, and the act performed is known as an illocutionary act. Austin acknowledges that “force” can be regarded as part of “meaning”, when the latter is used in a broad sense. But Austin thinks it is better to distinguish force from meaning with the latter used in a narrow sense, or what we called the more constant, inherent side of meaning. Thus, interpreted, force, or illocutionary force, may be said to be equivalent to speaker’s meaning, contextual meaning, or extra meaning. The third sense in which to say something can mean to do something concerns the consequential effects of a locution upon the hearer. By telling somebody something the speaker may change the opinion of the hearer on something, or mislead him, or surprise him, or induce him to do something, etc. Whether or not these effects are intended by the speaker, they can be regarded as part of the act that the speaker has performed. This act, which is performed through, by means of, a locutionary act, is called a perlocutionary act. The difference between illocutionary act and perlocutionary act is that one is related to the speaker’s intention and the other not.

Defined in this way, the locutionary act is what linguists have been studying all along. That is, how sounds, words and sentences are made, and what inherent meanings they have. The perlocutionary act involves many psychological and social factors, of which we are still more or less in the dark. So the illocutionary act is what Austin really drives at. In this sense, speech act theory is in fact a theory of the illocutionary act. In this general theory then, which applies to all sentences, the original performatives are only a special type in which the illocutionary force is made explicit by the performative verb.