Thursday, November 8, 2012

A simple argument that the PSR is necessarily true or necessarily false

Aron Zavaro, in correspondence, supplied me with the following simple central idea for this argument: If the Principle of Sufficient Reason (PSR) were contingently true, there would be no explanation of why it is true.

So the PSR is either necessarily true or necessarily false.

10 comments:

Drew said...

How do you define the PSR, and how do you reconcile it with libertarian free will?

Alexander R Pruss said...

See either my PSR book or this.

Heath White said...

This is a neat little argument.

It works, I think, iff explanations must entail their explananda. For suppose they don't have to entail their explananda. Then the PSR can be contingent so long as I can give an explanation of the PSR which does not entail it.

Alexander R Pruss said...

It depends. While some things do have non-entailing explanations--say, outcomes of stochastic processes--it is hard to see a very plausible story on which the PSR has such an explanation.

Houdini said...

Dr. Pruss, I have a question concerning Koon's epistemological argument--I believe you presented a shortened version in your Leibnizian Cosmological Argument. It seems as if Koons is arguing that if ~PSR is true then it's possible that our perceptual states are brute facts (either part of the time or all of the time). Therefore, we could have no trust in our perceptual sates. But, of course, even if ~PSR is true it still might be the case that our perceptual states aren't brute facts and that perhaps other things in the external world are. In fact it might be the case that only one thing is a brute fact, or three, or three-hundred. But ~PSR doesn't necessarily entail that our perceptual states are brute facts. But this means that Koons is arguing from mere possibility. That is, if it's even possible for ~PSR to be violated--and to be violated with regards to our perceptual states--then we can have no trust in the veracity of our perceptual states.

If Koons is basing his argument off of mere possibility (i.e. that PSR isn't necessarily true and can possibly be violated) then, even if ~PSR were false and PSR true we would still fall into radical skepticism concerning our perceptual states. It's logically possible, even if PSR is true, that we are brains in vats or being controlled by some higher power (Descarte's demon for example). And since it's possible that these scenarios are true then, like Koons' argument, we can't trust our perceptual--heck!--even our cognitive states. So it seems to me that Koons' argument is actually too broad. If we're going to argue from mere possibility that ~PSR entails radical skepticism concerning our perceptual states, then we should equally affirm radical skepticism with regards to demon or brain in vat scenarios (seeing how they are possible scenarios).

Houdini said...

Well not so much a question as it is a criticism. I'm wondering if you can answer it.

Alexander R Pruss said...

My preferred move is that if PSR is false, then one cannot say that such sceptical scenarios are *unlikely*, because no meaningful probabilities can be attached to violations of PSR.

Houdini said...

I'm not even sure we can determine the probability of these sceptical scenarios even with PSR. For suppose we take the evil demon route. Any attempt to prove that such a scenario is unlikely would presuppose that our cognitive faculties are reliable and can subsequently draw a conclusion from certain evidences. But if such a demon existed then we couldn't trust our cognitive faculties at all.

Alexander R Pruss said...

We might have a deductive argument for the existence of God, and then argue that God isn't likely to allow much in the way of such demonic deception.

But more generally, I think that if our metaphysics commits us to the non-unlikeliness of a sceptical scenario, then either we should doubt that metaphysics or we should be sceptics.

Houdini said...

Yes but using a deductive argument against an epistemic scenario like the demon would be to presuppose that one isn't already in the grasps of the demon and can consequently rely on their cognitive faculties to make a sound deductive argument. How can one tack any degree of probability to a sceptical scenario without presupposing that the sceptical scenario is false?