Thursday, October 29, 2009

Presentism and "ago"

According to most proponents of presentism, propositions are tensed. Thus, when yesterday you said that it is raining and I said it today, we expressed the same proposition, which, perhaps, was false yesterday and is true today. Moreover, presentists believe that one cannot refer de re to non-present objects.

For presentism to have any hope of being able to express all of reality, the presentist needs an "Ago" operator, where Ago(t,p) is a proposition that backdates p by t (units of time). If p is expressed by a present tense sentence, Ago(t,p) can be expressed by a past tense sentence. Thus, if p is the proposition that it is raining, Ago(3 days,p) is the proposition that three days ago it was raining.

Here is a plausible fact about the logic of "Ago":

  1. Ago(t,p) is now true iff p was true t units of time ago
The seriously actualist presentist adds this:
  1. No proposition that refers de re to a presently non-existent entity can be true. (If we like, we can probably qualify this as: "no positive proposition".)
Let p be the proposition that there is someone who will vote for Obama. Then:
  1. Ago(70 years,p) is true.
I.e., 70 years ago, there was someone who would vote for Obama. Thus, by (1):
  1. p was true 70 years ago.
But p makes de re reference to Obama. Since Obama didn't exist 70 years ago, it follows by (2) that:
  1. p was not true 70 years ago.
And this, of course, contradicts (4).

Thus, the presentist cannot hold (1)-(3) together.

Thus, the straightforward presentist reading of the claim that 70 years ago there was someone who would vote for Obama as the claim that 70 years ago someone existed who would vote for Obama is one that doesn't fit with (1) and (2). But there is a non-straightforward way of giving the truth-conditions that does:

  1. There (is) a time t at which there (is) a person x who (votes) for Obama at t and who also existed on October 29, 1939,
where "(is)" is short for "was, is or will be" and "(votes)" is short for "voted, votes or will vote".

An interesting question is whether such truth conditions are available for all possible examples of this sort.

There is, however, a different route for the presentist. She could deny (1). This would be analogous to Robert Adams' move of allowing that a proposition might be true at a world without being such that were that world actual, the proposition would be true. Such a view a view, when married to Crisp's concept of abstract times, would have the problematic consequence, that in general, at a time t, the time t was not present. (For t will contain propositions that make de re reference to now-actual objects that didn't exist at t, and so at t the maximal proposition would have been different from what it actually is.) To me, (1) seems very plausible.

Probably, most presentists will simply deny (2), allowing for de re reference to non-existents by means of haecceities. They will then open themselves to Lewis's objection that they are not really presentists, but there is probably a way out of that. It would, however, be an interesting thing if they had to deny (2)—this would mean that presentists cannot be serious actualists in the sense involved in (2). And if presentists could not be are not serious actualists, then their claim that only present objects are actual is not quite as revolutionary as it seems.


Mike Almeida said...

But p makes de re reference to Obama. Since Obama didn't exist 70 years ago, it follows by (2) that:
p was not true 70 years ago.

But certainly actualists can truthfully say, 'possibly, Obama does not exist', where 'Obama' does not refer to him in that possible non-actual world. It rather refers to Obama in our world, despite being embedded in the possibility operator. Presentism should allow for the same thing when names are embedded in the 'ago' operator. It's true that Obama did not exist 70 years ago or it was the case 70 years ago that Obama did not exist. 'Obama' in that proposition refers to the currently existing Obama.

Andrew said...

I don't see how the presentist is open to this response, since Obama didn't exist 70 years ago, and if 'Obama' used 70 years ago referred to the Obama who exists now, then the use of 'Obama' 70 years ago must be referring to a non-present thing _at the time of 70 years ago_.

I am missing how the actualist's response would be analogous to the the presentist's one. (If I am just being thick-skulled, please just ignore my comment...I will just let it steep a bit more).

Alexander R Pruss said...


p is true only if p exists, just as Socrates sits only if Socrates exists.

Therefore, assuming presentism, if p was true 70 years ago, p existed 70 years ago. But if the actualist presentism is true, then, etc.

I agree that modal actualists can say "possibly, Obama does not exist." However, they cannot say this: "possibly, the proposition that Obama does not exist is true." Here, I am thinking of "serious" actualists like Robert Adams who do not admit haecceities.

Adams (in his thisness and actuality piece) then makes the move of distinguishing what is true in a world and what is true at a world. p is true in a world only if p exists and has the property of truth in that world. p is true at a world if p correctly describes that world. So, possibly, Obama does not exist, but it is not possible that the proposition that Obama does not exist is true (i.e., there is no world in which it is true).

The presentist can, it seems, make the very same move. But to do that will require the denial of (1).

Alexander R Pruss said...

By the way, I wonder if this problem isn't a red herring. Consider the simpler and more obvious problem: "Seabiscuit existed." What can the actualist presentist say about that?

Mike Almeida said...


I think the Adam's move is exactly the one presentists should make. Distnguish a proposition being true at a time and (if you will) in a time. (1) would have to be modified to read,

1. Ago(t,p) is now true iff there was a n (-t units) at which p,

where I assume that what is true in a time is also true at a time, but not vice versa. We can then say that it was true at t (= 70 yrs. ago) that Obama did not exist, but it is not true in t that Obama did not exist.
I concede that the distinction does not go comfortably from worlds to times.

Mike Almeida said...

Actually, it would be better to contrast truth at a time and truth about a time. It is true about the time t (=70 yrs ago) that Obama does not exist but it is not true at time t that Obama does not exist. That seems to work out nicely for presentists.

Alexander R Pruss said...

Yes, that sure sounds better.