Wednesday, September 16, 2009

Presentism and vagueness

  1. If presentism is true, then necessarily: if t is present, then x exists at t if and only if x exists simpliciter, x exists definitely at t if and only if x exists simpliciter definitely, x exists vaguely at t if and only x exists simpliciter vaguely.
  2. There can be vagueness about existence at a time.
  3. There cannot be vagueness about existence simpliciter.
  4. Any time can be present.
Then by 2, suppose that t is such that at t there is vagueness about existence at t. By 4, t might be present. By 1, it follows that if presentism is true, there can be vagueness about existence simpliciter. By 3 and modus tollens, presentism is false.

I think 3 is very plausible. The idea that, say, I might vaguely exist seems absurd. However, 2 is also very plausible. Think of the vagueness in the moment of a brute animal's death. (Human death is not the cessation of existence, so human death is beside the point.)

The weakness in the argument is that one might take 2 to be strong evidence for the denial of 3. Suppose there is vagueness in the moment of conception, so that at at the actual world w0, it is vague whether Bucephalus exists yet at t0. Then take a world w1 which is a duplicate of everything in w0 up to and including t0, but with everything getting annihilated after t0. Plausibly, at w1 it will be vague whether Bucephalus exists. Here, I would bite the bullet if I accepted 2. I would say that it's vague whether a world w1 that contains Bucephalus is a duplicate of w0 up to and including t0, or whether the duplicate is a world w2 that doesn't contain Bucephalus. This is a hard bullet to bite, but it is better than allowing for vague existence.


Jonathan D. Jacobs said...

Do you think it's a harder bullet to bite than denying 2? That's my initial inclination. (I don't know the vagueness stuff well enough to have more than an inclination.)

Alexander R Pruss said...

I don't know. I think the assessment of that will differ from person to person. For instance, if one has God involved in things coming into existence (he starts sustaining) and in things coming out of existence (he stops sustaining), then there is some reason to think 2 is false.

Mike Almeida said...

There can be vagueness about existence at a time.

Grant that it is not vague whether x exists or not, and grant that x exists. The open question is whether it is indeterminate that x is at t (for some time t). Certainly there is vagueness with respect to spatial location. So, presumably there can be vagueness with respect one's frame, and so vagueness wrt whether one is at time t.

Alexander R Pruss said...

The problem, though, is that some of the reasons for thinking there can be vagueness in respect of temporal location are also reasons for thinking there can be vagueness in respect of existence. But my argument requires that there be vagueness in respect of temporal location but not in respect of existence. And presentists probably are going to bristle at spatial analogies. :-(

Martin Cooke said...

...e.g. I would so bristle! I would rather deny either 2 or (as you say, given 2 then) 3. Regarding the former, consider the example you gave for 2 (vagueness in the moment of an animal's death) in more detail. There will be senses in which the animal is a bit alive, and senses in which it is dead. So there are all these different ways in which the animal can be said to be alive, or to exist.

The general principle is that to exist is to exist as one of a kind, and that the vagueness comes from the variety of possible kinds. So if we specify our terms more precisely, the vagueness goes away. The vagueness is not really there, it is an illusion caused by the imperfections of our languages. So there is not really vagueness about existence at a time (except insofar as there can be vagueness about existence simpliciter).

There would, if I'm right, be no vagueness about our existence at any time, because we are real individuals, not aggregates of molecules that conveniently take various names at various times, and because Presentism is true. Were 4-dimensionalism true, and were spatial vagueness about existence possible (not just the existence of spatially fuzzy things, presumably) then you would be right.