A speech act is a linguistic and philosophical term referring to any action that involves the uttering of words. There are no firm grammatical rules for a speech act; everything from full sentences to single words are included. They can include statements, speech that accomplishes something, and words that have some kind of effect. A speech act may be divided into one of several categories: utterances, illocutionary acts, and perlocutionary acts. All three can be prepositional acts if they refer to the same topic.
An utterance act refers simply to the speaking of any words. An illocutionary act accomplishes something with the act of speaking, for instance making a vow, a threat, or a command. This contrasts with a perlocutionary act, which achieves a voluntary or involuntary effect with the act of speaking, such as persuading or insulting. Utterance, illocutionary, and perlocutionary acts could all also be prepositional acts if they refer to the same theme or topic — for example, "You are bringing the flour," "Bring me the flour!" and "If you bring me the flour, I'll bake a cake."
In linguistics, researchers classify speech acts into these categories based on their effect on the environment. The terms illocutionary and perlocutionary acts were first used by John L. Austin, who published an influential book in linguistics, How to Do Things with Words, in the 1860s. John R. Searle later combined ideas from Austin and other researchers in the field into a larger theory. He also introduced the concept of the prepositional act.
Prior to these modern researchers, human interest in speech acts goes all the way back to Aristotle. In his time, the Greek philosopher believed only in the importance of those statements that deal with truth or fact. He did not believe that other speech act, like a question or command, was of any importance.
This changed in the 18th century with the Scottish philosopher Thomas Reid. He understood that language is composed of not only factual statements, but also theoretical elements like promises, commands, or warnings. Reid also believed that some linguistic structures are common to all languages and actually derive from the universal way human minds think.
Despite Reid's theory that all humans think alike, it has since been shown that problems may arise when individuals attempt to perform speech acts in a foreign language. Some speech acts may involve idiomatic expressions that are different from those in the native language. Different social conventions among different cultures may also call for different speech acts in some situations.