An Argument for Primitive Persistence

The first premiss of our argument is that time necessarily involves change—by which I mean that time necessarily involves happenings or events.¹⁵⁶ I do not want to imply by this that there could not be time in a universe which was qualitatively indistinguishable from one moment to the next (nor, though, do I particularly wish to defend the suggestion that there could be time in such a universe). All I am saying is that it is partly constitutive of the notion of time that every period of time should contain events or happenings, and that events or happenings are to be understood as changes. Nor do I want to insist, here, that all changes are necessarily changes to something or in something which persists (even though I am sympathetic to that view, as I made clear in Chapter 4): that

156 In ‘Time without Change’ (reprinted in his Identity, Cause, and Mind ), Shoemaker argues that at least in some logically possible worlds it could be reasonable to hypothesize that a period of time had elapsed during which nothing whatever had changed in any way. I am not persuaded by his argument, though I cannot discuss it here. But, in any case, it is clear that the argument cannot be construed as establishing that time might pass in the absence of any change whatever without presupposing that the persistence of objects in such a world would not be grounded in spatiotemporal-cum-causal conditions on sequences of momentary entities (such as durationless ‘time-slices’), since the continual comings-to-be and ceasings-to-be of such entities would precisely constitute changes during the supposedly changeless period of time (even though no qualitative change need be involved in such a case). So Shoemaker's argument, even if it is correct, cannot be used to any effect against me by adherents of the views of persistence which I am attacking, at least as far as my first premiss is concerned.

would be too easy a way to try to secure our desired conclusion. For present purposes, we can characterize the nature of change by saying that whenever a change occurs, something begins to be the case which was previously not the case—for instance, it begins to be the case that a light is glowing or that there is noise in a certain room.¹⁵⁷Change in this sense could conceivably still occur even in a qualitatively unvarying universe—for it might begin to be the case, say, that something was yellow where previously something else qualitatively indistinguishable was yellow.¹⁵⁸ (Whether this really is possible depends on whether the relevant version of the principle of the identity of indiscernibles is valid—an issue which I shall not go into here.)

The second premiss of our argument is that a change can only occur if there is something which persists through that change. Again, it is not being urged that a change must be understood as a change in or to something which remains the same throughout that change. For it is at least arguable that some events are not changes in or to things at all. All that is being urged is that when something begins to be the case which was previously not the case (that is, when a change occurs), there must exist at the time of the change something which also existed prior to the change. For suppose on the contrary that nothing existing at the time of the change existed prior to the change: that would of course imply that everything in existence at the time of the supposed change had begun to exist at that very time. However, what is it to say this, but to say that the time in question was the beginning of the universe and hence the beginning of time itself? (I am assuming, I hope fairly uncontroversially, that time would not exist in an empty universe.) But the beginning of time cannot be the time of any change in our sense, since we cannot truthfully speak of anything's beginning to be the case then which was previously not the case.¹⁵⁹ Hence we have reduced our original supposition to absurdity.

No doubt this reasoning may appear sophistical on first sight, but I

157 It is customary when discussing change to distinguish between ‘real changes’ and ‘mere Cambridge changes’: e.g. between Socrates's dying and Xanthippe's becoming a widow. But since the latter sort of change is apparently parasitic upon the former (in the sense that the latter sort of change can only occur provided the former sort does), it is not crucial to my argument to restrict the sense of change it invokes to that of ‘real’ change—nor, hence, is it crucial for me to tackle the difficult issue of defining the precise difference between the two sorts of change.

158 Thus consider a universe containing just two balls, one yellow and the other red but otherwise qualitatively indistinguishable from one another: and then suppose that at a certain moment the yellow ball turns red while the red ball turns yellow (and nothing else changes). It seems that the states of such a universe before and after the change would differ only in respect of the identities of the ball which was red and the ball which was yellow.

159 This means that if we want to call the beginning of the universe an event, we had better make this an exception to the rule that events are changes.

believe that deeper examination will vindicate it. Suppose I tell you that nothing that has existed between now and five minutes ago existed more than five minutes ago: what can you make of this but that I am saying that the entire universe began to exist five minutes ago? The earth, the sun, the stars—all these and everything else existing now or in the past five minutes began to exist, I tell you, no earlier than five minutes ago: how could you accept this and yet still give credence to the thought that there were events occurring more than five minutes ago? Ex hypothesi, no record of any such events could possibly now exist. So what would warrant our talking of these supposed events as having occurred more than five minutes ago rather than talking of them as belonging (at best) to an altogether different space-time continuum—another ‘possible world’?

But perhaps you will dispute the suggestion that no record of these supposedly earlier events could now exist—urging that this trades on an ambiguity in the term ‘record’. A record may either be an object bearing a trace of some earlier event, or it may just be an effect of some earlier event (in short, it may be what I have just called a ‘trace’). But, you may contend, it is only in the first sense of ‘record’ that records of the supposed events could not exist in our hypothesized case: there might still be states of presently existing objects which could be attributed to causes which occurred more than five minutes ago. However, it seems to me that to argue in this fashion is to beg the very question at issue. Our question is what reason we could have, in the hypothesized case, to suppose that any events might have occurred more than five minutes ago: it is no answer to say that we could attribute various states of presently existing objects to causes which occurred more than five minutes ago without explaining with what justification we could suppose causal relationships to be capable of reaching more than five minutes into the past. After all, the putative causes of these present states would themselves be events in the very category under dispute. Furthermore, I find it very difficult to see how any such justification could be forthcoming: for how could the required causal influences have been propagated in the absence of any objects surviving from the supposed earlier time into the current five-minute period? No photons, for instance, transmitted from objects existing in the supposed earlier period could be received by us—for all existing photons, being persisting things themselves, would ex hypothesi have existed for no longer than five minutes.

It shouldn't be thought, incidentally, that my reasoning in this matter is motivated by a crude verificationism: the point is not that, in the hypothesized case, the predicate ‘occurred more than five minutes ago’ would be devoid of meaning because no empirical evidence could warrant its application. On the contrary, I am presupposing that the predicate would be

meaningful in the hypothesized case, while contending on metaphysical grounds that nothing could made its application true in that case. After all, what I am urging is that, in the hypothesized case, the statement ‘Some event occurred more than five minutes ago’ would, of metaphysical necessity, be false—not that it would be ‘meaningless’. And the reason why it would be false is that in that case the universe itself—which, after all, would be one of the things presently existing—would have come into existence only five minutes ago and with it time itself.

The third premiss of our argument is that if there were nothing whose persistence was ungrounded, then everything's persistence would ultimately have to depend upon a succession of (suitably interrelated) changes. This may demonstrated with the aid of the two rival approaches to persistence discussed earlier—the property instantiation approach and the temporal parts approach—both of which contend that there is nothing whose persistence is ungrounded. According to both of these approaches, the persistence of any object is to be regarded as consisting in the obtaining of certain spatiotemporal-cum-causal relations between non-persisting entities of some sort. According to the first approach, the non-persisting entities in question are momentary instantiations of appropriate properties at certain place-times. According to the second approach, they are momentary ‘time-slices’ of persisting objects. However, this means that both approaches must regard the persistence of any object as depending upon a succession of changes. On the temporal parts approach this is quite evident, since each of the supposed time-slices of a persisting object has to come into being and each such coming-to-be constitutes a change necessary for the continued persistence of the object in question. But it is equally evident on the property instantiation approach too. For—taking a tomato again as our example of a persisting object—this approach must presume that tomatohood is freshly instantiated at each moment in the history of a single tomato: and each such fresh instantiation once more clearly constitutes a change necessary for the continued persistence of the tomato in question. (For an adherent of the property-instantiation to deny that tomatohood need be freshly instantiated at each moment in the history of a tomato would be tantamount to an admission that tomatoes simply persist—ungroundedly—at least through some periods of time.)

So, the three premisses of our argument are as follows: (1) time necessarily involves change, (2) a change can only occur if there is something which persists through that change, and (3) if there were nothing whose persistence was ungrounded, then everything's persistence would have to depend upon a succession of changes. From (1) and (2) we can infer that (4) time can only exist if there is something which persists through time.

(This is obviously not to say that any one thing must persist throughout the whole of time, just that there can be no period of time during which no persisting object exists.) But, also, from (2) we can infer that (5) if anything persists through time, then there is something whose persistence does not depend upon a succession of changes. For if everything's persistence depended upon a succession of changes, there would be nothing whose persistence through change could render those changes possible in the way required by (2). (I shall return to this claim in the next section, where I shall defend it against a certain objection.) Then, from (5) and (3) we can infer that (6) if anything persists through time, then there is something whose persistence is ungrounded. Finally, from (4) and (6) we can infer that (7) time can only exist if there is something whose persistence is ungrounded. And this completes our argument.