Tuesday, December 2, 2008

A sound argument against necessary tensism

Necessary tensism is the thesis that necessarily tensism is true.

  1. Tensism holds if and only if everything that exists in some way, either existed, or exists presently, or will exist. (Definition)
I think a lot of presentists are tensists. The "exists in some way" is a tricky thing. Maybe it should be glossed as: "can be quantified over"?

Here is an argument that tensism is not a necessary truth. In all of the premises, "the present" and tensed expressions must be taken to narrow temporal scope. I take definitions to be necessary truths. I will use "exists*" as an abbreviation for "existed, exists presently or will exist".

  1. Two times are temporally related if and only if they are simultaneous or one is earlier than the other. (Definition)
  2. Necessarily, if x existed, then it existed at a time earlier than the present. (Premise)
  3. Necessarily, if x will exist, then it will exist at a time later than the present. (Premise)
  4. Necessarily, if x exists presently, then it exists at a time simultaneous with the present. (Premise)
  5. Necessarily, if x exists*, then x exists in some way. (Premise)
  6. It is possible for there to exist in some way an entity at a time not temporally related to the present. (Premise)
  7. Necessarily, if tensism holds and x exists in some way, then x exists in some way at a time temporally related to the present. (By (1)-(6))
  8. Possibly, tensism is false. (By (7) and (8))
No tensist will be convinced, I suppose, since they will deny (7) (they may quibble about other premises, but I don't think these are a big deal). But I think (7) is very plausible. Surely it is possible for there to be parallel time lines with no temporal relations between them. Likewise, surely it is possible that there be no fact of the matter to the effect that a short-lived entity on Alpha Centauri has existed pastly, and no fact of the matter that it exists presently, and no fact of the matter that it will exist futurely. (One just thinks a little about relativity theory, and this becomes plausible.)

Moreover, not only is it possible that tensism is false, but we are not in a position to know tensism to be true. For we are in no position to know that there are no parallel timelines, and if there are, then tensism is false.

5 comments:

larryniven said...

I'm a bit confused - why can we not match up parallel timelines to get multiple presents, multiple pasts, and multiple futures? Especially if we assume that everything that exists began to exist at some point, every universe - i.e., every set of time-space axes - can be matched up at time 0. Just because we say that something exists now doesn't mean that it exists now and here, does it? If so, then parallel timelines wouldn't really help much here.

Alexander R Pruss said...

I think the notion of multiple presents does not make sense. That would be a case of one present, in multiple locations.

And while in fact everything contingent began to exist at some point, it is far from clear that this is a necessary truth. And if it's not, then there will be worlds where stuff has always existed.

larryniven said...

Okay, but leave that second thing aside for the moment - I'm not even sure the question makes sense anyway. Just assume for the sake of argument that everything had to begin to exist and that therefore we can at least match up each timeline with another in the obvious way. I still don't see why we can't be satisfied with one present in multiple places, so to speak. The problem, I thought, was that we don't have an obvious way to differentiate between the past, present, and future of other universes from where we are - that, in other words, your use of "the present" in 7 means "our present." And yes, while we have no way of relating our present to the current value of t in any other universe, why not simply say (on the assumption that the universe had a beginning) that, for any time t in our universe, the "present" in any other universe is the time that was t minutes (or whatever unit) after 0? That would establish, or so it seems to me, a good enough relationship between our timeline and any other timeline to say whether something in another universe existed before, during, or after something in our universe.

If that's too complex, is the following a fair representation of tensism:

Tensism holds if and only if everything that exists in some way in a given universe, either existed in that universe, or exists presently in that universe, or will exist in that universe.

I honestly just don't know enough about the view to say whether this does anything harmful to its intentions, but it seems like a common sense qualification to me: would they really want to say that something that exists in one universe used to exist in another? That's just weird. But if we accept this, then your 6 and 7 are irrelevant, no?

Mike Almeida said...

Tensism holds if and only if everything that exists in some way, either existed, or exists presently, or will exist. (Definition)
I think a lot of presentists are tensists. The "exists in some way" is a tricky thing. Maybe it should be glossed as: "can be quantified over"?


Help me with this view, Alex. I take presentists to quantify only over those things existing simpliciter. The set of things that exist simpliciter is the set of presently existing things. Of course these things can have the property of existing at tn (where tn is some future time), but the quantifier in, 'there is some x such that x exists at tn' is restricted to things now existing. But presentists don't want to deny that something existed in the past without presently existing, right? So, I'm wondering about your definitnion of tenism above.

Alexander R Pruss said...

Mike:

Well, your presentist will be a tensist, since she will say that everything that exists simpliciter exists presently (and hence exists, existed or will exist).