Thursday, September 8, 2016

Presentists can't reduce time

Historically, some philosophers have attempted to reduce time to something else, say change or the causal nexus. It's interesting to note that this cannot be done if presentism is true. For to reduce time to something else requires giving a nontemporal account of the "wholly earlier" relation between events. But if presentism is true, there never exist two events one of which is wholly earlier than the other. For if one of them is present, the other is not. And only present events exist given presentism.

Now, of course, the presentist has a way of talking about non-present events. She can, for instance, use the temporal modal operators WAS and WILL. However, she cannot do so in the course of reducing time to something else, since WAS and WILL already presuppose time. The presentist must take time to be primitive, thus.

In particular, this means that Aristotle, who attempted to reduce time to change, cannot be consistent if he is a presentist.


Tom said...

Somewhat related to this, how is it that a presentist can have an arrow of time? If there is no past or future, what sense does it make to say that one event occurs after another? To take an analogy: if the only real location is New York City, what sense does it make to say that any other location is north or south of it?

Alexander R Pruss said...

I think the presentist can use any of the standard theories about the arrow of time. She can say, for instance, that the order of time is the order of causation, or that the order of time is the order of increasing entropy, or that it is grounded in the fundamental difference between the WAS and WILL modal operators.

Alexander R Pruss said...

A partial response to my post has occurred to me. Suppose the presentist takes as a primitive a single modal operator NONPRESENTLY. Then she might be able to talk about non-present events using that modal operator, and then give an account of time.

But she has to resist the claim that NONPRESENTLY = WAS or WILL. She has to hold that NONPRESENTLY is a fundamental modal operator. That seems implausible to me. It seems very plausible that NONPRESENTLY is disjunctive in nature.

Tom said...


But it seems that the standard theories of time presuppose the reality of the past. For instance, if we use entropy to ground an arrow of time, I take it that there has to be a past state of affairs in which entropy was low. If all that exists is the present, then does it even make sense to say that the past had lower entropy?

David McPike said...

"if presentism is true, there never [presently] exist two events one of which is wholly earlier than the other." - Right... But how anyone could deny this consequent (regardless of what they think about 'presentism')?

Alexander R Pruss said...


I didn't write "presently exist". I wrote "exist". An eternalist can say "exists", without relying on temporal operators and without limiting the existence to the present. The presentist can only do that by using some locution like "existed, exists or will exist". But she can't use that locution if she's trying to reduce time.

DAS said...

We should also consider what we know about time from a physics perspective. A corollary of the Heisenberg Uncertainty principle is that we cannot be entirely certain about exactly when any event occurs. There is some minimum unit of time similar to the minimum unit of length (Planck Length) over which there is uncertainty as to when an event occurred.

Thus there is no infinitesimally dividable element of time. There is some non-zero chunk of time that has to exist in order for Quantum Mechanics to work its magic.

This seems to me that it could be the stake through the heart of presentism.

Michael Gonzalez said...

DAS: Uncertainty over when an event occurred is merely an epistemological problem. The event occurred at some exact instant, even if we are barred by various physical constraints from determining exactly when that was.