use–mention distinction two ways in which terms enter into discourse – used when they refer to or assert something, mentioned when they are exhibited for consideration of their properties as terms. If I say, ‘Mary is sad,’ I use the name ‘Mary’ to refer to Mary so that I can predicate of her the property of being sad. But if I say, ‘ ‘Mary’ contains four letters,’ I am mentioning Mary’s name, exhibiting it in writing or speech to predicate of that term the property of being spelled with four letters. In the first case, the sentence occurs in what Carnap refers to as the material mode; in the second, it occurs in the formal mode, and hence in a metalanguage (a language used to talk about another language). Single quotation marks or similar orthographic devices are conventionally used to disambiguate mentioned from used terms.
The distinction is important because there are fallacies of reasoning based on use–mention confusions in the failure to observe the use– mention distinction, especially when the referents of terms are themselves linguistic entities. Consider the inference: (1) Some sentences are written in English. (2) Some sentences are written in English. Here it looks as though the argument offers a counterexample to the claim that all arguments of the form ‘P, therefore P’ are circular. But either (1) asserts that some sentences are written in English, or it provides evidence in support of the conclusion in (2) by exhibiting a sentence written in English. In the first case, the sentence is used to assert the same truth in the premise as expressed in the conclusion, so that the argument remains circular. In the second case, the sentence is mentioned, and although the argument so interpreted is not circular, it is no longer strictly of the form ‘P, therefore P’, but has the significantly different form, ‘ ‘P’ is a sentence written in English, therefore P’. See also CIRCULAR REASONING , METALAN- GUAGE , PHILOSOPHY OF LANGUAGE , TYPE – TOKEN DISTINCTIO. D.J.