Use–mention distinction

In analytic philosophy, a fundamental distinction is made between the ordinary use of a term versus the self-aware mention of it. The distinction between use and mention can be illustrated with the English word "cheese":

Cheese is derived from milk.
Cheese is derived from the Old English word ċēse.

The first sentence is a statement about the edible substance called "cheese". It demonstrates a or ; the writer is using the normal English word "cheese", in its typical way, to refer to the common dairy product. The second is a statement about the very word "cheese" itself as a linguistic entity. This second sentence provides a ; the writer is mentioning the word but not using it to refer to anything other than itself.
The use–mention distinction can sometimes be pedantic, especially in simple cases where it is obvious. 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.

Overview

In written language, words or phrases often appear between single or double quotation marks or in italics. In philosophy, single quotation marks are typically used, while in other fields italics are more common. Some style authorities, such as Strunk and White, emphasize that mentioned words or phrases should be visually distinct. On the other hand, words or phrases do not carry typographic markings.
The phenomenon of a term having different references in various contexts was referred to as suppositio 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:

With a : "That is my pig."
With a : "Santa Claus's pig is very big."
With a : "Any pig breathes air."
Metaphorically: "Your grandfather is a pig."
As a : "Pig has only three letters."

The use–mention distinction is particularly significant in analytic philosophy. Confusing use with mention can lead to misleading or incorrect statements, 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.

Commentary

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:
Issues arise when a mention itself is mentioned. Notating this with italics or repeated quotation marks can lead to ambiguity.
Some analytic philosophers have said the distinction "may seem rather pedantic".
In Limited Inc, a 1977 response to analytic philosopher John Searle, Jacques Derrida mentioned the distinction as "rather laborious and problematical".