 Some may reply that we are still talking about different abilities. In contrast to the case in which the opera singer sometimes cannot sing, your attempt to carry out retro-suicide inevitably fails. The opera singer is able to sing operas because he has shown it before and can demonstrate it again, but the attempted retro-killer has not proved and can never prove his ability. Therefore you are never in a situation where you can kill your younger self. If we accept this objection, we may reformulate the solution by saying that the contextual solution explains why you should be able to retro-kill your younger self under the appropriate circumstances. But, again, how can we talk about the ability to make retro-suicide relative to certain facts at all, if there are no possible worlds in which you carry out your deed. It seems reasonable to say that you have the ability to do something if there is a possible world in which you carry out this action. This is true of the opera singer. He can sing operas because he does it in a possible world in which he has not lost his voice. But you cannot make retro-suicide because there is no possible world in which you kill your younger self. You are unable, even in principle, to do so.