Your complimentary articles

You’ve read one of your four complimentary articles for this month.

You can read four articles free per month. To have complete access to the thousands of philosophy articles on this site, please

SUBSCRIBE NOW

Time, Identity & Free Will

To Be Is To Persist

Dustin Gray finds out that continuing to exist isn’t as simple as you might think.

What does it mean for an object to persist through time? Consider the statement, ‘My car is filthy, I need to wash it.’ Consider the response, ‘How did it get that way?’ The answer is that dirt, dust and other particles have collected on the car’s surface thus making it filthy. Its properties have changed. At one point in the car’s career, none of that dirt and grime existed on its surface and the car was said to be clean. The fact is that for a car to get dirty, the extension of time is necessary. The standard view of identity is that each thing is entirely itself at any given time. So how can an object remain identical with itself over time, if it changes its properties? In many ways I have different properties now than those I had last week. But if I am different, how then can I be the same?

The objective of this article is to answer the question of what it means to say that we and other things persist through time. First I’ll lay out two popular philosophical views of persistence through time, then I will present possible problems with both views. After that, I will outline another possible answer that lies outside of these views. Finally, I will provide my own answer.

Endurance & Perdurance

Image © Paul Gregory

Before unwrapping the popular views, let me introduce two key terms, the first of which is concrete particular. A concrete particular is an entity which comes into existence at a certain time, passes out of existence at some later time, and exists at all the times in between. Its career is ‘temporally bounded’. Examples include human beings, animals, plants, chairs, and hamburgers – as opposed, for instance, to abstract ideas, such as 1+1=2. A concrete particular is what we usually mean by a ‘thing’ or ‘object’.

The second term is diachronic sameness, which literally means ‘the same thing at two times’. If I say something has diachronic sameness, I am saying that “an individual existing at one time is the same object as an individual existing at some other time” (Metaphysics: A Contemporary Introduction, Michael J. Loux & Thomas M. Crisp, 2017, p.224). Having diachronic sameness means I can accurately describe myself as being the same concrete particular that I was last year, two minutes ago, or when I started typing this sentence.

Like the notion of time itself, on the face of things, all this seems to be common sense. All of our pre-philosophical intuitions tell us this story, and it is a widely accepted one.

In these terms, one answer to the question of what it means to persist through time is that throughout its career a concrete particular is wholly present at each of the different times at which it exists: that is, for any one time that X exists, all of the parts that X has are present at that time.

This is the account given by endurantists. Endurantists maintain a steadfast hold on the notion of diachronic sameness, claiming that at any one time in its career, object X is identical with X at any other time it exists. So expressions like ‘the Jack of today’ and ‘the Jack of yesterday’ are referring to one numerically identical concrete particular whose spatial parts are wholly present at any given time throughout Jack’s existence. The endurantist will claim that an object’s spatial parts are the only genuine parts of it.

By contrast, the account of persistence through time known as perdurantism claims that along with a thing’s spatial parts, it also has temporal parts. Perdurantists argue that over and above the three dimensions of space, there exists a fourth dimension in which an object’s temporal parts exist; so that Jill yesterday, Jill today, and Jill tomorrow, are different parts of Jill. These expressions do not pick out one numerically single object, rather they refer to numerically different parts of a single thing. Its persistence through time consists in its being an aggregate of different temporal parts present at different times. For the perdurantist, these temporal parts are just as real as spatial parts: temporal parts have properties just like spatial parts – such as the property of ‘being Jill last week’. So, along with having spatial extension – for example, fingers and toes – the perdurantist will claim that a concrete particular also has temporal extension – for example, Jill yesterday, Jill today and Jill tomorrow. There are also temporal parts of temporal parts. An example of this could be that Jack this morning is a temporal part of Jack today.

Endurantism is the standard or normal view of objects. Perdurantism is typically seen as a counter to the standard view. Given this, the perdurantist must go to greater lengths not only in justifying her account, but in objecting to claims made by endurantists as well.

Possible Problems

The endurantist’s claim that a concrete particular is numerically identical at different times, when it has different properties, is to deny a principle from G.W. Leibniz (1646-1716) accepted by most philosophers, known as the Indiscernibility of Identicals. It states that necessarily, if x=y, then x and y must have all the same properties.

This is a problem for endurantists, but one that perdurantists find easy to navigate. Given the claim of perdurantists that a thing has temporal parts, they can easily account for changes in properties through time. They will say that bearded Jack is simply one of the many temporal parts of Jack, just as is Jack with a clean shave.

The perdurantist can easily explain Jack’s change in properties throughout time by following this line of reasoning. However, the endurantist will have more work to do. Consider a metaphysician named Henry being tanned in the Summer while surfing in Hawaii, and pale in the Fall while locked in his office busily grading undergraduate papers. Henry’s properties have changed. This difference in properties implies that Henry in the Summer does not equal Henry in the Fall. The endurantist’s burden is to prove how tan Henry has the same properties as pale Henry, which he must have in order to be the same concrete particular, according to the Indiscernibility of Identicals (Metaphysics, p.236).

In response to this worry, the endurantist might suggest that Henry has both the property of being tan and of being pale; he just exemplifies them at different times. Being tan and pale can be expressed by Henry having time-indexed properties; for instance, tan-in-Summer and pale-in-Fall.

However, it seems that the perdurantist has a leg up here. (This argument is taken from David Lewis.) Recall the perdurantist’s claim that concrete particulars persist through time due to their having temporal parts? They will insist that although tan Henry and pale Henry are different, both the former and the latter are parts of a single collection of Henry’s temporal parts. The upshot is that the perdurantist can maintain our pre-philosophical intuition that Henry does indeed persist as the same individual through time, and since he persists as an aggregate of interconnected, albeit different temporal parts, there is no denial of the Indiscernibility of Identicals.

Image © Paul Gregory

Another Possible Answer

Now I want to bring to light a possible alternative answer to the question of how we and other things persist through time that lies outside of endurantism and perdurantism.

Closely related to, but certainly distinct from perdurantism, is exdurantism, or stage theory. Like perdurantists, stage theorists believe in the existence of temporal parts, and hold them to be what a thing’s persistence through time consists in. However, they deny that a concrete particular is an aggregate consisting of its temporal parts. Instead, they say that each stage of an object’s career is a separate distinct object. Stage theorists label these stages counterparts, which proceed or follow one another almost instantaneously. The difference is, that for perdurantists, a persisting object exists in stages; for exdurantists, the same object exists as stages. Sally Haslanger, a professor of philosophy at MIT, sums the notion up nicely by saying of stage theory that, “Although on this view ordinary objects are stages and so (strictly speaking) only exist momentarily, they can nonetheless persist by virtue of having counterpart antecedent and/or successor stages” (The Oxford Handbook of Metaphysics, Michael J. Loux & Dean W. Zimmerman, eds, p.318, 2003).

So on this theory there is no whole made up of temporal parts, only distinct stages. However, the succession of separate, distinct stages doesn’t seem to give a satisfactory explanation of something’s persistence through time. Imagine that you toss a tennis ball downward, so it bounces off the floor, and lands back in your hand. Stage theory tells us that the ball’s persistence through time consists in a succession of different spatial stages of the ball. In describing the matter specifically, an exdurantist would use the expression ‘ball moving downward’ to designate the existence of a distinct and separate counterpart; followed instantaneously by the counterpart ‘ball bouncing’; followed instantaneously by the counterpart, ‘ball moving upward’, and so on. Again, these are not stages of tennis balls, but stages as distinct balls. Each stage consists of a different object – which implies that the tennis ball does not actually persist through time, especially when we consider the mere momentary existence of each variant stage. For how could such instantaneous ‘things’ have temporal extension?

This brings up the main difference between stage theory and the other views we have looked at so far. In claiming that concrete particulars exist in a succession of distinct and separate stages, the exdurantist seems to be painting a picture of objects unable to persist through time. If each stage is a completely separate entity, we lose all continuity, and thus lose persistence through time. The entire theory rests upon the inability of a thing to be temporally extended.

Let’s see how well the view defends itself. Looking into my past, I can make the true statement, ‘‘I was an immature teenager’’. There seems to be no conflict with any of my pre-philosophical intuitions in my saying so. More specifically, the statement doesn’t conflict with any of the views I’ve elucidated so far. The endurantist would explain the statement by talking about my numerical identity across time, and to explain the difference between me now and then, remind us of her notion of time-indexed properties. Analysis by the perdurantist would conclude that my existence as an immature teenager signifies one of my many temporal parts. But what if I were to say, ‘‘I still am that immature teenager? For I am still the same concrete particular, am I not?’’ In this instance both these views hold water, but the stage theorist’s view falls short due to her central claim that my existence as an immature teenager is a separate and distinct counterpart succeeded by my existence as a (somewhat) mature adult. The stage theorist might object that by using the ‘I am’ version of the statement I think I refer to the same thing as when I use the ‘I was’ statement, but in the strict sense decreed by her theory, this is not the case. (For more on this, see Theodore Sider, ‘All the World’s a Stage’, Australasian Journal of Philosophy 74, 1996.)

There is another similar but stronger objection to stage theory. Critics of this view might point out that saying ‘I persist through time’ is the same as saying ‘I exist at many times’. According to stage theorists’ central claims, they cannot make the former statement, and, in fact, cannot effectively utter the latter statement either. The stage theorist could only truly paraphrase the former statement by saying, ‘Separate and distinct mes exist in their own times’.

Although I find stage theory to be thought-provoking, objections like these lead advocates of both endurantism and perdurantism to conclude that the view is flat-out false, and I tend to agree with them.

My Proposed Answer

All paths taken so far in search of an elegant and fortified answer to the question of how we and other things persist through time have led to a myriad of objections and dead ends. So where can we turn now? In this final section, I want to propose an answer to the question that, though not extravagant, serves as a fitting response, with less objectionable precepts than those of the theories we’ve already looked at.

The view I advocate, known as presentism, tells us that what is real is only what exists now. To the presentist the past and future simply don’t exist. Reality is not temporally extended. The present is the only real time. “To be real and to be present, the presentist wants to say, are one and the same thing” (Metaphysics, p.214).

Opponents will ask of the presentist how she can give an accurate description of events that took place in the past; for instance, what she did last week. She will claim that there’s no inherent problem in giving a clear account of events that have transpired – with the fundamental qualification that those events no longer exist. And the same could be said for events that might take place in the future. Those events may be predicted, but they are not real, yet. Until an event is happening in the present moment, no degree of reality is ascribed to it by the presentist.

Let’s conduct a closer inspection by considering the sentence ‘George Washington had false teeth’. It can be agreed upon by both professional historians and well-educated children that this expresses a true proposition. What can the presentist say about this? Their central claim is that objects and the events that transpired in the past are not real. But is not this proposition a true one, and so referring to reality? The presentist could respond by saying that it’s a true proposition about conditions that used to exist but no longer do.

Let’s see how presentism handles the difficulties incurred by the other views. With no ascription of reality to the past or future, the worry of change in properties experienced by the endurantist is of no consequence to the presentist. And, since the only temporal part that could be said to be real for the presentist is the momentary one of now, we can seemingly hold on to the perdurantist’s notion of temporal parts; however, under the presentist’s view, the temporal extension is that across the timespan of now, so there is actually only one temporal part to be concerned with! Finally, recall the stage theorist’s inability to describe themselves as the person they once were. It is tempting to say that presentists are in the same predicament. However, this inability to describe herself as the person she once was is of no consequence to the presentist, because the person she once was simply no longer exists. Nor does there exist the person she will be. There is only the person she is now. But still the question remains, how do we and other things persist through time? By saying that the only real time is now, we seem to be saying that we do not persist through time, because our past and future selves don’t exist. What kind of answer is that?

I would reply first that to describe events accurately, we must use accurate tenses, saying that events in the past existed and events in the future will exist. When we do so, my claim that the only real time is now still holds water, and I can also effectively describe past and future events. Additonally, I would say that in the strictest sense, we do not persist through time. However, I would like to add that if the only real time is now, then within that one and only real time, I can do nothing but persist. Therefore, all that is necessary for me and other things to persist through time, is to be. To persist is simply to exist… in the now.

Dustin Gray is a PhD student at the University of California, Santa Cruz whose interests include metaphysics and philosophy of technology.