So one of the problems advanced against libertarian accounts of free will is that while perhaps Suzy’s doing A for some set of reasons R, given the choice between A and B, may be explained, it isn’t explained why Suzy did A rather than B. Clearly, though, Suzy is the explanation for AvB. Now, if the libertarian is at least able to get this far, then the problem is going from Suzy being the explanation for, or cause of AvB, to her being the cause of A (supposing A is her choice in the actual world).
Pruss in his book offers us a principle which is worth some consideration here, and which I hadn’t really reflected sufficiently on previously. He calls it the Principle of Disjunctive Causation (PDC). If Suzy is the explanation for AvB, then she must be that which brings it about that AvB. However, she can only do this, it seems, by actually bringing about A, or bringing about B. Thus, a principle can be articulated thus:
Any immediate cause of a disjunctive state of affairs is also the cause of at least one of the disjuncts – indeed, it is a cause of the disjunctive state by being a cause of a disjunct state or states.
~ Pruss, PSR p.143
If this principle is sound then so long as the libertarian can explain that Suzy is the cause of AvB, then whichever disjunct obtains subsequently is the disjunct she causes, because she cannot be the cause of B if B is non-actual, she must be the cause of at least one of the disjuncts if she is the cause of the disjunction, and “stating the cause of something does explain it” (Pruss, 143).
Pruss runs through three clever counter-arguments against the principle, and diffuses them all pretty easily. However, I wonder about the underlying assumption, namely that that which is caused is explained. Perhaps the objector to libertarian free will will argue that just because some quantum mechanical event, say a particle fluctuating into extension, is clearly ’caused’ by the quantum vacuum state, does not mean that that the particle fluctuated into extension really is explained by the quantum vacuum state.
However, let’s imagine that the principle holds enough intuitive appeal to be persuasive, and let’s imagine that it can be applied to the quantum mechanical event (though it is harder, perhaps, to argue that an aimless indeterministic process acts as a cause of it’s effect in the same sense as a libertarian-free person taking aim at some end, and intentionally bringing it about; but let’s just bracket that kind of consideration out for the moment). The only question is whether identifying the cause of A is sufficient to explain A. If it is, maybe this principle does hold promise for solving the paradox of libertarian free will. However, as with the quantum vacuum state, I imagine that we will always be able to ask ‘why did it do so, rather than not’? This will lead us back into the more general problem with contrastive explanations.