Indexical Thought

This entry will describe some of the main philosophical and psychological puzzles that arise concerning the kinds of thoughts that are expressed using indexical terms such as I, here, and now. These will include some puzzles concerning the relation between perspectival and objective modes of thought, the significance of indexical thoughts for the thinker's actions, the possibility of the same indexical thought being entertained by different thinkers or by the same thinker at different times, and the nature of thoughts about oneself.

An indexical is a linguistic expression whose reference varies in a rule-governed way with the context of utterance. Standard examples include here, now, and I, which normally refer to the place, time, and speaker of the utterance, respectively. Indexical thoughts are thoughts expressible using indexicals. Indexicals, as the word is used here, are to be distinguished from demonstratives such as that, whose reference also varies with context but not in the same rule-governed manner (note, however, that some writers use indexical or demonstrative for all context-sensitive terms). There is much debate about communication using indexicals (e.g., concerning messages saying “I am not here now”) but because indexical thoughts need not actually be expressed, or might be expressed only in internal monologue, we can largely set these problems of communication aside.

Indexical thoughts raise many puzzles. Some concern the fact that to represent the world indexically is to represent it from one's own perspective or point of view. This is often described in terms [Page 407]of egocentricity. To think of a place as nearby and to the left, for example, is to think of it as an egocentric location in an egocentric frame of reference determined relative to the thinking subject. Indexical thoughts are subjective in that they represent the world from the subject's point of view. Perception is similarly perspectival. Yet we can describe many states of affairs without using indexicals, and scientific descriptions of the world should normally avoid indexicals. Much of our conception of reality thus seems to require that we possess map-like or allocentric representations of the world, that is, representations from no particular point of view. One major question, then, concerns how our egocentric and allocentric representations relate to each other and, indeed, how we come to have a conception of an objective, mind-independent reality at all.

One qualification should be mentioned: Now is an indexical because its reference varies according to the time of utterance. But according to some theories in metaphysics (A-theories), past, present, and future are real, objective properties of times, whereas according to other theories (B-theories), they are relations analogous to left, up, or near. Hence, if the A-theory is correct, temporal indexical thought represents the world in an objective, non-egocentric way, whereas if the B-theory is correct, temporal indexical thought is egocentric in the same way as spatial indexical thought.

Indexical thoughts have a special significance for action. In John Perry's famous example, when one notices a trail of sugar along the supermarket floor leaking from someone's shopping trolley one thinks “someone is making a mess.” But when one realizes that the sugar is in fact leaking from one's own trolley one thinks “I am making a mess,” and one acts in a different way. Similarly, believing that the meeting begins at 3 p.m. does not have the same significance for one's actions as believing that the meeting begins in two minutes, or now, or half an hour ago. Merely knowing that one should head north is of no practical use in itself; one needs to know which way north is in egocentric terms, for example, to the right. Thus, as Perry observed, indexicals are essential: One cannot adequately describe an indexical belief-state using only non-indexical vocabulary, and perhaps one cannot act at all unless one represents the world indexically.

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