Harry Frankfurt is credited (by some) with having shown that alternate possibilities are not necessary for freedom and moral responsibility. There are any number of Frankfurt-style counterexamples (FSC) to the principle of alternate possibilities (PAP) and any number of (more or less relevant) versions of PAP. There are, further, any number of (more or less cogent) replies to each of the counterexamples. The literature is vast. I want to suggest a rather direct reply that (as far as I know) hasn’t been suggested and that does not depend on any specific version of the FSC. I will consider a brief counterexample with just a few bells and whistles, add the ornaments that you think matter. First, the sort of PAP that matters to the discussion is something like PAP0.
PAP0. S is free and morally responsible for what he has done only if S could have done otherwise.
It’s important to note that PAP0 does not apply to cases where we had choices to do otherwise but now cannot do otherwise (I could have tied myself to the mast, but now I cannot resist the Sirens). Cases like the following aim to show that PAP0 is false (I borrow liberally from Fischer here, but change the story a bit)
Black has secretly inserted a chip in Jones’s brain that enables Black to monitor and control Jones’s activities. Black can exercise this control through a sophisticated computer that he has programmed so that, among other things, it monitors Jones’s voting behavior. If Jones were to show any inclination not to rob the bank then the computer, through the chip in Jones’s brain, would intervene to assure that he actually decides to rob the bank.