  The rough characterization of indexicals in the first sentence of this article might be rejected by some theorists, for it relies on the notion of a linguistic expression (such as ‘you’) varying in reference, and content, among contexts. But some theorists instead describe indexicality in terms of expressions varying in reference or content relative to utterances or other sorts of speech acts, such as assertions. Other theorists speak of utterances or tokens varying in reference or content, without any relativization to context or speech act. Some theorists speak several ways. The differences may be theoretically significant, and more will be said about them below. In addition, some philosophers would prefer to speak entirely about shifts in extension, rather than shifts in reference, from context to context. Some theorists, for instance, hold that ‘you’ is not a singular term that refers to an individual in a context. Rather, it is a quantifier phrase, and so its extension, in a context, is not an individual, but rather a certain sort of set. (See section 5.2 below for an analogous view of complex demonstratives.) Such a theorist may also wish to use the term ‘reference’ only for expressions whose extensions are individuals. This article, however, will use ‘reference’ and ‘extension’ more-or-less interchangeably. On this use of ‘reference’, the word ‘you’ varies in reference from context to context, even if it is a quantifier phrase whose extension, in a context, is not an individual, but a set.