 To make this point clear, let us look at how the standard Frankfurt case would have to be amended to make it a close analogy to the situation of infallible foreknowledge. As Zagzebski has argued (1991, chap. 6, sec. 2.1), the device implanted in Mary’s brain would have to be set in such a way that no matter what Mary did, it never intervened. It is not even true that it might have intervened. Any world in which Mary decides to commit the murder is a world in which the device is set to make her commit the murder should she not decide to do it, and any world in which she does not decide to commit the murder is a world in which the device is set to prevent her from deciding to do it if she is about to decide to do it. Now of course this might be an impossible device, but it would have to be as described to be a close analogy to the foreknowledge scenario. And our reactions to this amended Frankfurt case are very different from typical reactions to the standard Frankfurt case. In the standard case it at least appears to be true that the agent cannot do otherwise, whereas in the case amended to be parallel to the foreknowledge case there is a very straightforward sense in which the agent can do otherwise because her will is not thwarted by Black in any reasonably close possible world. The machine is ready to manipulate her, but it does not manipulate her, nor might it have manipulated her since it does not even manipulate her in counterfactual circumstances. We might think of the machine as a metaphysical accident—an extraneous addition to the story that plays no part in the sequence of events in any possible world. Possibly it is not clear in the amended story whether or not Mary has alternate possibilities. What the story shows, then, is that alternate possibilities are not always relevant to the possession of libertarian freedom.