La Segunda República en Ronda 1. El tejido asociativo

I want to move on now to the problem of persistence. As I remarked in the opening paragraphs of this chapter, theories of the persistence of objects through time are commonly divided into two classes: perdurance theories and endurance theories. Standardly, the theories are characterized as follows.¹⁴⁵ According to the perdurance account, an object persists through time by having different temporal parts at different times at which it exists, whereas according to the endurance account, an object persists through time by being ‘wholly present’ at each time at which it exists. (I have to say that I find the expression ‘wholly present’ less than fully perspicuous, but I take it to mean, at the very least, that persisting objects do not have temporal parts.) The debate turns, then, on the question of whether or not persisting objects have temporal parts.

Unfortunately, the very term ‘temporal part’ has a number of different possible meanings, and is very difficult to clarify in any useful sense. One thing we need to be clear about is that the notion of a temporal part of a

144 Certainly, that is the way in which both David Hume and David Lewis approach the analysis of causation: see David Lewis, ‘Causation’, i n hi s Philosophical Papers, vol. ii (New York: Oxford University Press, 1986).

145 See further Lewis, On the Plurality of Worlds, 202. See also my ‘Lewis on Perdurance versus Endurance’, Analysis, 47 (1987), 152–4, reprinted in H. Noonan, ed., Identity (Aldershot: Dartmouth, 1993). In this paper I criticise an important argument offered by Lewis in support of the perdurance theory. I argue more positively on behalf of the endurance approach in my ‘Substance, Identity and Time’, i n my ‘Primitive Substances’, and in Chapter 5 below.

persisting object is not, for the purposes of the perdurance versus endurance debate, to be assimilated to the notion of a temporary part of a persisting object. The leg of a chair might be a temporary part of it, if it is a replacement for the original leg while the latter is undergoing repair. But such a chair leg is itself a persisting object, which will itself have temporal parts if all persisting objects do. Of course, some philosophers apparently do hold that at least some temporal parts of persisting objects are themselves persisting objects—as when David Lewis likens a temporal part of a person to a short-lived person.¹⁴⁶But, clearly, this is not a view which a perdurance theorist would do well to take about all temporal parts, since that would deprive him of any non-circular account of persistence. Sometimes, temporal parts of persisting objects are purportedly introduced to us as entities representable by ordered pairs of objects and times—for instance, by the pair 〈Napoleon, 5 June 1805〉-—and such an entity, we are led to suppose, might be referred to by a complex noun phrase such as ‘Napoleon on 5 June 1805’. Whether one can concoct entities in this easy fashion is a matter for debate, but even if one can, it seems plain that a temporal part thus conceived is both conceptually and ontologically posterior to the persisting object (here, Napoleon) of which it purports to be a part. So jejune a notion of temporal part accordingly seems of little use in a metaphysical account of the persistence of objects—as is demonstrated by the fact that even an endurance theorist need apparently have no special qualms about countenancing the existence of temporal parts thus conceived.

Is there, then, any acceptable notion of temporal part that is robust enough to serve a useful metaphysical purpose?

Well, it is sometimes urged that events and processes, at least, clearly have temporal parts in a robust sense of this sort.

(I take a process to be a sequence of temporally successive events, the events in the sequence being parts of the process.) We talk, after all, of such items as an early part of the performance of a certain play, such as the performance of its first scene. In like manner, we may talk of an early or late part of a persisting object's existence or life—though here I would agree with those who insist that this does not of itself entitle us to think that there are such entities as early or late parts of that object. But still, it may be urged, even if it is indeed open to debate whether such entities exist, at least we have now hit upon an intelligible way of talking about the supposed temporal parts of persisting objects which can be put to use in the metaphysical debate as to whether or not such objects persist

146 See David Lewis, ‘Survival and Identity’, i n hi s Philosophical Papers, vol. i(New York: Oxford University Press, 1983), 76.

by perduring. (If we couldn't even talk intelligibly about the possibility of objects having such parts, the debate could never get started; though I suppose some might say that that would be no bad thing.)

Now, I don't think it would necessarily be fair to protest that to model the supposed temporal parts of persisting objects upon the supposed temporal parts of processes in this way is simply to reduce persisting objects to processes.

(Certainly, though, I would want to reject any such reduction because, as I explained earlier, I take an ‘Aristotelian’ view of events and processes as consisting in changes and unchanges in the properties and relations of persisting objects.) Even so, I have serious doubts about the attempted analogy with events and processes. For I am not sure that even they have ‘temporal parts’ in any metaphysically significant sense. The performance of the first scene of a play is, no doubt, a part of the performance as a whole. (Processes, as I said a moment ago, are sequences of events, which are parts of them.) But in what sense is the performance of the first scene a temporal part of the whole performance? In the sense that it occurs, or comes into existence, before the rest of the performance? But if that were all there were to its being a temporal part, then, it seems, the proposed analogy between the ‘temporal parts’ of events and the ‘temporal parts’ of persisting objects would require us to regard the temporary parts of persisting objects as ‘temporal parts’ of them. After all, the replacement leg of a chair, which is a temporary part of it, may come into existence before or after certain other of its parts; so that if all that is required for something to be a temporal part of a persisting object is that it be a part of it and come into existence before or after other parts of it, then the replacement leg is as good an example of a ‘temporal part’ of the chair as anything could be. Nor will it help much to point out that an ‘earlier’ part of the performance of a play ceases to exist before its ‘later’ parts begin to exist, whereas the temporary leg of a chair may go on existing even after it has been replaced as a part of the chair—for, clearly, the temporary leg could perfectly easily be destroyed in the course of removing it from the chair. Indeed, some temporary parts of persisting objects have to be destroyed in the course of removing them from the objects in question: for example, certain living parts of organisms.

It is true that, at the time at which the ‘later’ parts of the performance of a play exist, none of the ‘earlier’ parts still exists. But equally, in the case of a chair, there may be a time at which none of the parts—legs, arms, seat, and so forth—which it had at some former time still exists, all having been destroyed and replaced by newly fashioned parts.

Are we then to say that such parts of a chair are temporal parts of it? If we do, we shall clearly not be deploying a notion of ‘temporal part’ which can have any relevance to the debate between perdurance and endurance theorists of persistence, because such parts of a

chair are themselves just other persisting objects about the nature of whose persistence the debate is concerned.

My own view is that if any metaphysically significant notion of the temporal parts of persisting objects is to be constructed, then the proper analogy to make is not with items like the performance of the first scene of a play, but rather with the spatial parts of concrete things (whether these be persisting objects or events). And here I would point out that by a spatial part of, say, a chair, I do not mean something like one of its legs. Rather, I mean a spatially extended entity whose spatial boundaries are defined in relation to the chair: something such as the bottom three inches of one of its legs, or the left-hand half of its back as seen from the front. Clearly, concrete things can only have spatial parts thus conceived if the things in question are extended in space (this applies just as much to events as to persisting objects).

By the same token, then, concrete things can only have temporal parts, in the sense in which I want to speak of them, if those things are extended in time.¹⁴⁷ By this account, a temporal part of a persisting object would be a temporally extended entity whose temporal boundaries are defined in relation to that object. (One minor refinement has to be made at this stage: just as we may, in principle, need to admit two-, one-, and zero-dimensional spatial parts of things in addition to three-dimensional ones, so too we may need to admit zero-dimensional temporal parts of things if we admit one-dimensional ones—but nothing crucial hinges upon this point, since what is important is that we must indeed be prepared to speak of temporally extended entities if we are to talk of temporal parts in any metaphysically significant sense.)

So, then, a temporal part of Napoleon, if such an entity exists, would be a temporally extended entity whose temporal boundaries are defined in relation to Napoleon—thus the boundaries of one such part might be fixed by the date of his birth and the date of his tenth birthday. One might try to refer to such an entity by some such complex noun phrase as ‘Napoleon up to the age of ten’. (This notion of temporal part is, I believe, quite distinct from the ‘ordered pair’ conception discussed earlier, because the latter conception involved no commitment to the existence of temporally extended entities of any sort. And this is not just because each such pair contained only a single time: for, in the first place, it was not implied that the time in question had to be momentary—the example I gave actually specified a day—and, secondly, no material difference would have been made if instead of ordered pairs we had talked of ordered triples,

147 Here, I believe, I may be in agreement with Robin Le Poidevin, even though he wants to say that things are extended in time whereas I want to deny this: see Le Poidevin, Change, Cause and Contradiction, 60 ff.

each containing two times, for there would still have been no commitment to the existence of temporally extended entities.) What emerges from all this, if I am correct, is that the perdurance versus endurance debate doesn't really hinge upon issues in mereology (the study of part–whole relations) as such, but rather upon the question of whether anything—and here I include not only persisting objects but also events and processes—is extended in time, in anything like the way in which things are extended in space. But this is at bottom a question about the nature of time, rather than a question about the nature of things existing in it. The question is whether we can properly talk about time as being some sort of dimension of reality, relevantly akin to the three dimensions of space. (A word of caution here: there is an abstract or purely formal notion of dimensionality used, for instance, to describe perceptible colours as differing from one another along the three independent ‘dimensions’ of hue, brightness, and saturation—but in what follows I am concerned with a much more robust notion of dimensionhood for which spatial length, breadth, and height constitute the paradigm, all of these providing independent ways in which concrete things can be extended.)