 As an indexical, the referent of “I” varies with the context of utterance (see the entry on  indexicals).  That is, “I” refers to different people depending on who utters it. Following Kaplan (1977), it is common to think of the meaning of such terms as determining a function from context to referent. In the case of “I”, a natural proposal is the “Self-Reference Rule” (SRR), that the referent of a token of “I” is the person that produces it (Kaplan 1977: 491; Campbell 1994: ch. 3). “I” is thus, unlike “this” or “that”, a pure indexical, seemingly requiring no overt demonstration or manifestation of intention (Kaplan 1977: 489–91). SRR captures the plausible thought that “I” is guaranteed against reference failure. Since every token of “I” has been produced, the fact that “I” refers to its producer means that there is no chance of its failing to pick out some entity. This account of “I”, then, treats it as not only expressive of self-consciousness, but also guaranteed to refer to the utterer.