Wednesday, May 30, 2018

Reattachment of fingers and a new Aristotelian argument for presentism

Suppose Alice loses her finger at t1 and at t2 it is reattached. Intuitively, after t2 she has the same finger as she had before t1. But now suppose that at t3 she loses her finger again, and it is reattached again at t4. Then at t1 and t3 she is shedding the numerically same finger. Do the two sheddings result in the numerically same severed finger (which is a finger in name only)?

It seems that the answer is affirmative—if we were right in thinking the reattached finger to be the same finger as the original one. For there seems to be a symmetry between re-shedding and re-attachment as we could replace shedding by a transplant operation when a finger is moved back and forth between two people (Terry Pratchett’s Igors probably do that sort of thing for fun sometimes), after all.

But here’s something metaphysically odd. Call the finger F and the severed finger S. Then there is a major metaphysical difference between the first and the second severing. Let’s think about the difference assuming eternalism. Then the first severing causes a severed finger to exist simpliciter. But the second severing does not cause a severed finger to exist simpliciter, but only to come to exist at t3. This is puzzling. In both cases, it seems that we have the same kind of cause, namely the severing of a finger, but the first time this has an ontic effect, a new being exists, and the second time it has no ontic effect. This seems wrong: the same kind of cause should have the same kind of effect, barring something indeterministic.

Maybe we could say that the finger’s coming to exist simpliciter is overdetermined by the severings. But this is counterintuitive. It shouldn’t be possible to add overdetermination to an effect already achieved, in the way that the second severing does. (Moreover, the overdetermination view conflicts with strong origins essentialism, which I accept, and the plausible counterfactual thesis that if the second severing didn’t happen, the very same severed finger S would have come into existence at t1 as actually did. For by strong origins essentialism, if an object was overdetermined in its origination, it could not exist without being thus overdetermined. But then if the second severing didn’t happen, S wouldn’t have been overdetermined, so it couldn’t exist.)

So we have a puzzle for eternalism (and growing block, too). One could even take the above line of thought as a direct argument for presentism. Informally:

  1. After reattachment, one has the same finger F as originally.
  2. If after reattachment one has the same finger as originally, then each severing results in the same severed finger S.
  3. The first severing causes S to exist simpliciter and presently.
  4. The second severing only causes S to exist presently.
  5. Both sheddings have the same kind of effect.
  6. So, existing simpliciter must be nothing but existing presently.
  7. So, presentism is true.

What should the eternalist (or growing blocker) say? It seems to me that the best move is to deny that both sheddings result in the same severed finger. The first results in S1 and the second results in S2 and S1 ≠ S2. By symmetry between re-shedding and re-attachment, I think we have to say that the reattached finger is numerically different from the original one, and deny (1). That is counterintuitive, but it seems the least costly response.

Objection: God could ensure that the reattached finger is the same as the original.

Respose: I think so. But that would be a miraculous intervention. And the symmetry would then require a similar miraculous intervention to ensure that the severed finger after the second shedding is the same as the severed finger after the first shedding. And this makes the second shedding causally different from the first, since no such miraculous intervention was needed to modify the first shedding. And with the two sheddings being different in kind, (5) will no longer be plausible.


Michael Staron said...

You seem to think that it is counterintuitive to hold that the two sheddings are numerically distinct severed fingers. But if we think that the two sheddings are numerically identical, then we are committed to the possibility of intermittent existence - S comes into existence for a time, goes out of existence, and then is brought back into existence for a time. And isn't intermittent existence counterintuitive as well? I don't think, then, that your solution is one to which the eternalist should be afraid to commit.

James Goetz said...

I agree with presentism, but both presentism and eternalism distinguishes between the respective t1, t2, t3, and t4. We need more than this scenario to disprove eternalism and support presentism.

Martin Cooke said...

Severing a finger hardly causes a thing to come into existence, and giving the severed finger a name is not going to make any difference. (I wonder too, about the severed finger losing molecules: are those new things? Why ever not?) If you are going to say that the severing produces a new thing, though, then it is not more odd to deduce that the second severing produces a second thing, imho. But I would say that there is a finger before the severing and the same thing after.

Alexander R Pruss said...

Mr. Staron:

Intermittent existence doesn't seem problematic. Forward time travel results in intermittent existence but seems quite unparadoxical. And one can dissassemble a watch, thereby destroying it, and then later reassemble it.

Mr. Goetz:

Sure, they distinguish between the times. But the argument isn't about that. It is about the weird way that two severings have very different effects given eternalism.

Mr. Cooke:

Well, that's the Aristotelian way of looking at it, and this is an Aristotelian argument. When you die, a corpse comes into existence. The corpse didn't exist before--your body did. Similarly, the severed finger is like a little piece of a corpse.

Modern-day Aristotelians dispute whether the molecules we shed are new things. The issue is this. After being shed they seem to be substances. But it is a central tenet of classical Aristotelian metaphysics that a substance does not have substances as parts. So given that tenet, either the molecules existed prior to shedding but not as substances--and the idea that something can change whether it is a substance is very strange--or else they came into existence when shed.