Indexicality is a special, systematic kind of context dependence which characterizes expressions such as I, here, or that. The linguistic meaning of indexicals contains a rule that constrains the ways in which their semantic value depends on the various features of the context of their use. If A utters a sentence which does not contain indexical expressions, and B agrees with A, B may simply repeat the sentence uttered. Treating the repetition of what somebody else uttered as constituting their endorsement would, however, end in failure with most indexicals.