An assertion is a speech act in which something is claimed to hold, for instance that there are infinitely many prime numbers, or, with respect to some time t, that there is a traffic congestion on Brooklyn Bridge at t, or, of some person x with respect to some time t, that x has a tooth ache at t. The concept of assertion has occupied a central place in the philosophy of language, since it is often thought that making assertions is the use of language most crucial to linguistic meaning. In recent years, by contrast, most of the interest in assertion has come from epistemology.

The nature of assertion and its relation to other categories and phenomena have been subject to much controversy. Some of the ideas of assertion will be presented below. The article will situate assertion within speech act theory and pragmatics more generally, and then go on to present the current main accounts of assertion.[1]

By an account of assertion is here meant a theory of what it consists in to make an assertion. According to such accounts, there are deep properties of assertion: specifying those properties is specifying what a speaker essentially does in making an assertion (e.g., express a belief). There must also be surface properties, which are the properties by which we can tell whether an utterance is an assertion, for instance that it is made by means of uttering a sentence in the indicative mood. Some accounts specify deep properties only, while others relate deep properties to surface properties, as we shall see.