Relative Identity
Deutsch (Harry)
Source: Stanford Encyclopaedia of Philosophy, 2002-7
Paper - Abstract

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Author’s Abstract

Identity is often said to be a relation each thing bears to itself and to no other thing (e.g., Zalabardo 2000). This characterization is clearly circular ("no other thing") and paradoxical too, unless the notion of "each thing" is qualified. More satisfactory (though partial) characterizations are available and the idea that such a relation of absolute identity exists is commonplace. Some, however, deny that a relation of absolute identity exists. Identity, they say, is relative: It is possible for objects x and y to be the same F and yet not the same G, (where F and G are predicates representing kinds of things (apples, ships, passengers) rather than merely properties of things (colors, shapes)). In such a case ‘same’ cannot mean absolute identity. For example, the same person might be two different passengers, since one person may be counted twice as a passenger. If to say that x and y are the same person is to say that x and y are persons and are (absolutely) identical, and to say that x and y are different passengers is to say that x and y are passengers and are (absolutely) distinct, we have a contradiction. Others maintain that while there are such cases of "relative identity1," there is also such a thing as absolute identity. According to this view, identity comes in two forms: trivial or absolute and nontrivial or relative (Gupta 1980). These maverick views present a serious challenge to the received, absolutist doctrine of identity. In the first place, cases such as the passenger/person case are more difficult to dismiss than might be supposed (but see below, §3). Secondly, the standard view of identity is troubled by many persistent puzzles and problems, some of recent and some of ancient origin. The relative identity2 alternative sheds considerable light on these problems even if it does not promise a resolution of them all.

A word about notation. In what follows, lower case italic letters ‘x’, ‘y’,etc., are used informally either as variables (bound or free) or as (placeholders for) individual constants. The context should make clear which usage is in play. Occasionally, for emphasis or in deference to logical tradition, other expressions for individual constants are employed. Also, the use/mention distinction is not strictly observed; but again the context should resolve any ambiguity.

  1. The Standard Account of Identity
  2. Paradoxes of Identity
  3. Relative Identity3
  4. The Paradoxes Reconsidered
  5. Absolute Identity
  6. Objections and Replies
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First published Mon Apr 22, 2002; substantive revision Mon Nov 5, 2007. Link.

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