Indexicality

In the philosophy of language, an indexical behavior or utterance is one whose meaning varies according to certain features of the context in which it is uttered. Now, here, and I are typical examples of indexical terms. I refers to whoever is speaking. Now refers to the time at which it is uttered. In linguistics, indexicality is usually referred to as deixis.

Indexicals are closely related to demonstratives (this, that), in that both vary in meaning depending on context. The difference is that indexicals do not require the user to indicate the object to which they are supposed to refer by means of a pointing gesture or other non-verbal means. Many if not all indexicals are also egocentric, which means that in order to successfully interpret them the hearer must know the respective speaker, time, and place of utterance.

Example
An episode of the Simpsons plays off of the popular character Smokey the Bear, whose motto is "Only you can prevent forest fires":


 * Robotic Smokey the Bear: Only who can prevent forest fires?


 * (Bart has the choice between the buttons "me" and "you" so he presses "you.")


 * Robotic Smokey the Bear: You pressed you referring to me. That is incorrect. The correct answer is you.

Bart selected the word which correctly completes Smokey's usual line. But the word "you" as uttered by Bart refers to a different person than when it is uttered by Smokey, and Smokey interprets Bart's answer as attempting to refer to the same person Smokey would refer to. Bart should use me to refer to that person, so (he says) Bart is wrong.

Other sources
David Kaplan's essay Demonstratives is widely considered one of the most important philosophical and logical discussions of indexical terms.

The phenomenologist Aron Gurwitsch's essay, 'Outlines of a Theory of "Essentially Occasional Expressions"', appearing in Gurwitsch's postumous work, Marginal Consciousness [1985], provides the classic statement on indexicality from a phenomenological standpoint. This paper was utilized by Harold Garfinkel in his formulation of the term, and is a cornerstone of the Ethnomethodological enterprise.

Gurwitsch's formulation is an elaboration, and radicalization, of the concept as it appears in Edmund Husserl's Logical Investigations(1900/1901).