On the Logic of Demonstratives |
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Kaplan (David) |

Source: Journal of Philosophical Logic, Vol. 8, No. 1 (Jan., 1979), pp. 81-98 |

Paper - Abstract |

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- In this paper, I propose to outline briefly a few results of my investigations into the theory of demonstratives: words and phrases whose
*in*tension is determined by the contexts of their use. - Familiar examples of demonstratives are the nouns 'I', 'you', 'here', 'now', 'that', and the adjectives 'actual' and 'present'. It is, of course, clear that the extension of 'I' is determined by the context - if you and I both say 'I' we refer to different persons. But I would now claim that the intension is also so determined. The intension of an 'eternal' term (like 'The Queen of England in 1973') has generally been taken to be represented by a function which assigns to each possible world the Queen of England in 1973 of that world. Such functions would have been called
*individual concepts*by Carnap. - It has been thought by some - myself among others - that by analogy, the intension of 'I' could be represented by a function from speakers to individuals (in fact, the identity function). And similarly, that the intensions of 'here' and 'now' would be represented by (identity) functions on places and times.
- The role of contextual factors in determining the extension (with respect to such factors) of a demonstrative was thought of as analogous to that of a possible world in determining the extension of 'The Queen of England in 1973' (with respect to that possible world).
- Thus an enlarged view of an intension was derived. The intension of an expression was to be represented by a function from certain factors to the extension of the expression (with respect to those factors).
- Originally such factors were simply possible worlds, but as it was noticed that the so-called tense operators exhibited a structure highly analogous to that of the modal operators, the factors with respect to which an extension was to be determined were enlarged to include moments of time.
- When it was noticed that contextual factors were required to determine the extension of sentences containing demonstratives, a still more general notion was developed and called an 'index'. The extension of an expression was to be determined with respect to an index. The intension of an expression was that function which assigned to every index, the extension at that index.
- Here is a typical passage ….

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