Use–mention distinction

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

The first sentence is a statement about the edible substance called cheese. It demonstrates a use or usage; 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 mention; 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, mentioned 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 (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 having different references in various 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:

• With a concrete and real referent: "That is my pig." (personal supposition)
• With a concrete but unreal referent: "Santa Claus's pig is very big." (personal supposition)
• With a generic referent: "Any pig breathes air." (simple supposition)
• Metaphorically: "Your grandfather is a pig." (improper supposition)
• As a pure term: "Pig has only three letters." (material supposition)

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.