In Chapter 5 of Deontic Morality and Control, Ishtiyaque Haji issues the following challenge:
“ Develop a prima facie plausible account of ‘S can do X.’ Then  show that in this very sense of ‘can’, the agent can both do X and refrain from doing X in a Frankfurt-type case, where X is the sort of action that the counterfactual intervener wants the agent to perform. I suspect that  any such account of ‘can do X’ will yield the result that in a Frankfurt-type case, the agent won’t be able to refrain from doing other than what she in fact does. [sic] This is because (i)  such an account will, in all likelihood, include a proviso to the effect that there are no external or internal impediments that prevent that agent from doing X or from refraining from doing X; (ii)  in Frankfurt-type cases, the counterfactual intervener ensures that the agent will lack opportunity to do otherwise even is she has the ability to do otherwise; so there will be an external impediment that prevents the agent from refraining from doing X; and (iii)  refraining her doing X requires both the ability and the opportunity to refrain from doing X. In turn, if this is all correct, then  we will have strong reason to believe that, in the proposed sense of ‘can’, it won’t be true that the agent will be able to refrain from doing what she in fact does if determinism is true.” (Haji, p. 69)
Here, I would like to accept the challenge and outline a response step by step.
1) Jones can ask Smith to marry her.
2) Suppose Black wants Jones to ask for Smith’s hand in marriage and has the power to generate in Jones’s mind the thought that she will propose to Smith because Jones loves Smith and has learned that she is pregnant with his child. But it just so happens that before Black can work his magic Jones asks for Smith’s hand in marriage because she loves him and is pregnant with his child.
3) Contrary to Haji’s suspicions, it is not that case that Jones cannot refrain from asking for Smith’s hand in marriage. This is so because FAP – ‘it is within S’s power to do X iff it is within S’s power not to do X’ – obtains. (Ibid. p. 45, cited in Zimmerman 1996:86-7)
4) In accord with Haji’s anticipation, it is true that we must include a proviso that there are no “external” impediments (like a broken telephone connection) or “internal” impediments (like either Jones or Smith falling unconscious) that prevent Jones from exercising her ability to propose to Smith or to refrain from doing so. But such a proviso only serves to hold the relevant variables fixed. If either type of impediment (both of Haji’s examples seem ‘external,’ to my lights, by the way) obtained, then neither the decision to propose to Smith nor the decision not to propose to Smith would be live options for Jones. But such a proviso does not rig the game; it merely sets the terms of play.
5) Though it is true that in FTCs the counterfactual intervener, here Black, robs the agent of the opportunity to do otherwise than she does, it does not follow from this, I argue, that Black’s presence in any way hinders the exercising of her power to do otherwise. For, according to FAP, the very ability to do other than X is exercised in the doing of X. For Jones, the very possibility of not asking for Smith’s hand in marriage (and the consequences that would follow from that course of action) plays a determinate role in her decision to ask Smith to marry her. If Jones could not entertain this possibility — if she could not understand what it would mean for her to refrain from marrying Smith — then she equally could not be said to have the power to make marriage proposals, to Smith or to anyone.
6) Despite Haji’s adamant insistence on this point, I do not think that having the power to refrain from doing X requires both the ability and the further opportunity to do so. I feel this way because on my view, those alternative possibilities that are sufficient to underwrite free-will, deontic anchors and moral responsibility are built-in to any power that satisfies the concept of a rational ‘ability’ in the first place. (I suppose this puts me on even ground with Fischer and Dennet, though I haven’t worked out the details of any specific alliances yet).
7) Since determinism — taken as the view that states that all the “non-relational” or “hard” facts of the past together with the laws of nature produce one definite future (Ibid. p. 60) — is only devastating to those who take opportunity to be the gold-standard of alternative possibilities against which we measure one’s moral responsibility and/or the existence of deontic anchors it matters not to my view of freedom, obligatoriness and responsibility whether or not determinism so construed obtains. This is because on my view (as laid out so far), an agent is only morally responsible for what she has the ability to do and not for ensuring for herself that she have, in every possible situation, the opportunity to express this ability. Likewise, according to what I’ve said thus far, the ‘can’ in ‘ought implies can’ refers only to ability and not to opportunity. And so, although determinism seems to render it preordained whether or not any given agent will have the opportunity to exercise her ability to do X and not do X, I offer a perspective on moral responsibility and obligatoriness that corresponds to only that range of an agent’s ability that is ‘called upon’ in any given situation.
I have hereby met Haji’s challenge and I have done so by holding fast to FAP, the principle that states that an agent can only do X if an agent can do not-X. However, Haji asked not just for any account, but for a plausible one, which would preserve deontic anchors in either a FTC or in a deterministic universe. And though I think that the view I have offered here is not only plausible but also true, I have yet to argue for its plausibility or to demonstrate its validity.
If I can show that a FAP-like principle holds not only for actions but for any and all determinations that range over a gradient of possibilities, including the “non-relational” or “hard” facts of determinism then I will shift the onus onto advocates of Haji’s style of moral nihilism to show why FAP should be rejected in the sphere of ethics while its equivalent principle — for now what I will call determinate negation — is not contested in the same way in other fields of metaphysics.