The Blockage Argument is designed to improve upon Harry Frankfurt’s famous argument against the Principle of Alternative Possibilities (PAP) by removing the counterfactual intervener altogether. If the argument worked, then it would prove in a way that Frankfurt’s argument does not that moral responsibility does not require any alternative possibilities whatsoever, not even the weakest “flicker of freedom” (such as the possibility of avoiding voluntary action).
Some philosophers have rejected the Blockage Argument solely on the basis of their intuition that the inability to do otherwise is incompatible with moral responsibility. I will argue, however, that it is not merely the inability to do otherwise by itself but rather the inability to do otherwise in combination with the absence of a counterfactual intervener that is incompatible with moral responsibility. If I cannot do otherwise and it is not because of a counterfactual intervener, then it must be the case that I am being forced to choose and therefore act as I do, in which case I cannot be morally responsible for this action.
Because the Blockage Argument fails, and because it was really the only way to establish that moral responsibility does not require any alternative possibilities whatsoever, it follows that moral responsibility does indeed require at least one alternative possibility in any given situation. But it turns out that this conclusion does not tip the balance in favor of incompatibilism over compatibilism. It would have if blockage and determinism were equivalent. But they are not. Unlike blockage, determinism is compatible with certain counterfactuals that compatibilists traditionally believed the ability to do otherwise reduces to. So even though moral responsibility is incompatible with blockage, it does not necessarily follow that moral responsibility is incompatible with determinism.
Levy, Ken, "Blocking Blockage" (2016). All Scholarship. 8.