Chisholm v. Classical Compatibilism: Part II

As part of his argument that PAP is not equivalent to PAPC, Chisholm makes the following inference:

(1) You couldn't have decided to do anything other than what you did decide to do.

(2) Therefore, you could not have done anything other than what you did do.

This seems correct, but I've been wondering what one might do to resist Chisholm's inference.

What if "could" means different things in each line? The word "could" is a shifty beast and it can be hard to police. For example, if the first line asserts that it was morally impossible (i.e. forbidden) to decide otherwise, but the second line asserts that it was logically impossible to do otherwise, then the inference would equivocate in a way that would defeat the transfer of warrant from line 1 to line 2.

The classical compatibilist's view that we ought to understand PAP as PAPC rests on the thought that "could" here is a practical modality. I can do something if and only if I have the ability to do it. The classical compatibilist then gives a counterfactual account of having an ability. Thus, the classical compatibilist's understanding of PAP (as PAPC) can be derived like so:

(3) You're accountable for x only if you had the ability to not x.

(4) You have the ability to not x only if had you decided to not x, you would have not x-ed.

(5) Therefore, you're accountable for x only if had you decided to not x, you have not x-ed.

An effective argument against the classical compatibilist, then, will be one in which the modality in play is understood as practical possibility.