TRANS-TEMPORAL IDENTITY
This concerns the problem of re-identification through time; that is, of supplying the grounds on which an individual b at time t 2 can be identified as the same individual a at an earlier time t A necessary condition of trans-temporal identity would seem to be spatio-temporal continuity. 45 In other words, we can say that a is identical with b only if there is a continuous trajectory connecting them, 46 or, in other words, that b and a should both be 'individual stages' in the succession of such stages which corresponds to the 'career' of a single persisting individual. This trajectory or career must then satisfy the following necessary conditions: 47
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I. |
The trajectory or succession must be spatio-temporally continuous. 48 However, there are an infinite number of continuous spatio-temporal paths between any two space-time points separated by a non-vanishing interval. Thus it has been suggested that a criterion of qualitative continuity is required. |
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II. |
The trajectory or succession must be qualitatively continuous in the sense that any individual stage on the trajectory or in the succession must be qualitatively similar to a neighbouring individual stage on the trajectory or in the succession. 49 This is still not enough, as I and II together would not prevent us from tracing an individual in such a |
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way that we combine stages of the individual with stages of some of its parts. 50 What is further required is a sortal constraint such that every individual stage in the succession falls under a sortal term S. 51 |
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III. |
There is a sortal term S such that the succession is a succession of S-stages or the trajectory underlies such a succession. 52 |
Of course, the S-stages themselves must be momentary in the sense that they do not depend on any criteria for reidentification through time.
Other conditions have also been suggested such as the requirement that the matter of which a thing is composed at one moment should be the same, or nearly the same, as the matter of which it is composed at the next moment and that there must be a causal relationship between individual stages. 53 It is not our intention to become involved in a detailed discussion of these further requirements here but it is worth noting that the causal criterion may obviously be related to I above. 54
In this context we can once again see the difference between the approaches to individuality delineated above. STI is more economical, metaphysically speaking, in the sense that it claims that it is the points of space-time (however they are understood) which confer individuality, distinguishability and trans-temporal identification. However, this conferral hinges on the Impenetrability Assumption 55 and any threat to the latter would undermine the whole edifice. According to the TI view, on the other hand, the points of space-time have only a secondary role to play in allowing us to infer a trans-temporal identification and it is something else, the underlying Lockean substratum or the primitive thisness of the object, which, ontologically speaking, confers the re-identifiability. And, as we shall see, the way in which we formally represent the notion of non-individuality will have an impact on our understanding of sortal terms and how they themselves are formally represented.
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