In the field of analytic philosophy, a fundamental distinction is made between the ordinary use of a term (a word, name, phrase, etc.) and the mention of the word itself. The distinction between using and mentioning a term can be illustrated with the English word cheese below:
The first sentence is a statement about an edible product of milk-producing animals. It uses the term; the writer is using the English word in its standard way to refer to the common dairy product. The second is a statement about the very word itself. This second sentence instantiates a mention; the writer is mentioning the word but not using it to refer to anything other than itself.
Invoking the use–mention distinction can sometimes seem pedantic, especially in simple cases where it is obvious what is being referred to. However, scholars argue that many philosophical works have been misguided, or misinterpreted by others, based on a failure to understand or recognize this basic distinction.
Referring to a word or phrase itself, rather than what the word or phrase normally refers to, is accomplished in written English by invoking single or double quotation marks or by using italics. In philosophy, single quotation marks are typically used, while in other fields (such as linguistics) italics are more common. Some style authorities, such as Strunk and White, recommend that mentioned words or phrases should be visually distinct. On the other hand, used words or phrases do not carry typographic markings.
The phenomenon of a term's having different references in different contexts was referred to as suppositio (supposition) by medieval logicians. Supposition describes how a term is substituted in a sentence based on its referent. For nouns, a term can be used in different ways:
The use–mention distinction is particularly significant in analytic philosophy. Confusing use with mention can lead to problems, such as category errors.
Self-referential statements also engage the use–mention distinction and are often central to logical paradoxes, such as Quine's paradox. In mathematics, this concept appears in Gödel's incompleteness theorem, where the diagonal lemma plays a crucial role.
Stanisław Leśniewski extensively employed this distinction, noting the fallacies that can result from confusing it in Russell and Whitehead's Principia Mathematica.
Donald Davidson argued that quotation cannot always be treated as mere mention, giving examples where quotations carry both use and mention functions.
Douglas Hofstadter explains the distinction between use and mention as follows:
When a word is used to refer to something, it is being used. When a word is quoted, the focus is on its surface aspects, such as typography or phonetics, and it is being mentioned.
Issues arise when a mention itself is mentioned. Notating this with italics or repeated quotation marks can lead to ambiguity.
In Limited Inc, a 1977 response to analytic philosopher John Searle, Jacques Derrida mentioned the distinction as "rather laborious and problematical".
In this 1995 paper, Boolos discussed ambiguities in using quotation marks as part of a formal language, and proposed a way of distinguishing levels of mentioning using a finite number of marks.