In many writings, Pruss has defended an argument for PSR from his Aristotelian-inspired causal powers view of modality. The way I understand it, I don't think the argument works, but that may be because I'm not really grasping it correctly, so it would be nice if someone could clear it up a little.

That view of modality, as I get it, is basically that every "purely possible" state of affairs can ultimately be caused by something (in other words, X is possible if there is something that can initiate a chain of causes leading to X holding).

The argument for PSR is as follows: say p is a false contingent proposition, and (given ~PSR) it is possible that p holds without an explanation. Then let p* be the proposition that p holds without a causal explanation. By the assumed account of modality, if p* is possible then there is something that can initiate a chain of causes leading to p* holding, but that is absurd since that chain of causes would causally explain both why p holds and that it holds without a causal explanation.

Now, the problem I have is it seems like p* is being reified/thingified in some illegitimate way here. Say p is a contigent thing (a chicken, for instance) and p* reports the brute existence of that chicken. It's not p* that needs a possible cause, but rather p. P* simply is p holding without a cause. A contigent chicken is possible because there is something that can initiate a causal chain leading to the existence of that chicken; p* is simply reporting the fact that the chicken does not actually have a cause. P* holds if p holds without an actual cause, that's all. It makes sense to think the chicken can have a cause, but why think "the chicken's existing without a cause" is something that can also be caused?

I guess this would be a criticism of that specific view of alethic modality. It makes sense to say positive states of affairs can be caused (the existence of a chicken can be caused; events such as the chicken eating corn can be caused; etc), but why say that a purely negative state of affairs like "X does not have a cause" is something that can be *caused*? How exactly does that work? It seems nonsensical.

Perhaps the argument isn't supposed to be read like that; perhaps the point is just that given that p* is always possible, it would have to be possible even in worlds in which p has a causal explanation, which is absurd. In other words, p is only possible if it can be caused; p* holds in w, therefore p holds in w; because p holds in w, p can be caused in w; but then p can be caused in w while, simultaneously, p* holds in w, which is absurd. Is that it? It would seem like a weird use of possible worlds since normally we'd think the conditions for p's possibility could be preserved by p having a cause in another possible world, not necessarily in w...

Am I overlooking something?

Last edited by Miguel (8/02/2018 1:34 pm)