Suppose that some person all of a sudden becomes the king of China, but only on the condition that he forgets what he has been, as if he were born anew; practically, or as far as the effects could be perceived, wouldn't that be the same as if he were annihilated and a king of China created at the same instant in his place? That is something this individual would have no reason to desire.
- Leibniz, Discourse on Metaphysics, c.34.
If you wish even to be equal to Peter in glory, you will be; I say "in glory", for you are not able to will to be Peter in person: for if you were to will this, you would will for yourself to be nothing - which you cannot will.
- Alexander of Canturbury, De S. Anselmi similitudinibus, c.64.
This issue comes up in theology, because the Devil's sin is said to be desiring to be equal to God. But how can a creature desire to be equal to God? This would be the same as desiring to be God, which is equivalent to desiring not to be a creature, which is to desire not to exist, or to desire that a finite creature be infinite and uncreated, which is a contradiction, and, as Aristotle says, impossibles do not lie within the realm of choice.
In the Ordinatio, Book II D.6 Q.1, Scotus resolves this difficulty by noting that there are two equivocal ways of understanding choice. One, the kind of choice Aristotle meant when he said that choice is about what is possible, is the termination of a practical syllogism: when I deliberate about the range of means available to achieve my goals, and my mind determines which is the best means for the best end, my will responds by choosing that end. So when I deliberate about how to get from Maryland to California, I weigh the possibility of getting groped by a government goon at the airport against the labor and expense and time of driving, and wonder whether in fact I want to make the trip at all. At length I make my choice. I don't deliberate about whether to teleport or take a wormhole shuttle, because these are not real possibilities for me.
However, in another sense I can incline my will towards anything my intellect can apprehend, whether possible for me or not. And my intellect can apprehend any proposition formed from simple intelligibles. "Being equal to God" is something my mind can grasp, since I can grasp that there is such a thing as God exists; and I can recognize that "Being equal to God" is something the will can desire, since God the Son can will to be equal to God the Father. - Likewise "being the king of China" or "being St Peter" is something I can recognize as intelligible, possible, and willable in itself. This doesn't imply that the object of my apprehension is possible for me and so able to be the subject of my will as a practical choice. Wishing for time travel is like this, in my opinion. The past was once the present, and so "being at such-and-such a date in the past" is intelligible and was once actual for certain people. So saying "I wish I were in 1310" is intelligible. There's no intrinsic contradiction about being in 1310. The only contradiction is in thinking that it's possible for me, as this person here and now, to be in the past. That would be more or less like me wishing to be Peter. Peter may exist, and I may imagine what it's like to be him, imagine having his experiences and so forth; but whoever is having Peter's experiences is Peter, not me. I can imagine the past, and wish that my own present was happening in medieval Oxford rather than modern America, but whoever had a life in medieval Oxford could not be me, since my life is necessarily the one being lived by me right now.
There must be some sort of disorder in the will if one wills for oneself what is impossible for oneself. The implication in such an act of will is that God's will in creating me was wrong, and instead of creating me he should have created something different, or abstained from creating. I thus set up my will in opposition to God's as superior. This is intrinsically different from willing unactualized possibilities for myself, such as being stronger, being wiser, being more virtuous (even being more wealthy), even desiring things which are possible but over which I have no power: that's the point of petitionary prayer.
It strikes me that some such set of distinctions as this can allow us to avoid the pitfalls of Nietzschean resentment, on the one hand, and the Nietzschean will of the eternal return, on the other. For if it's sinful to will in vain that one's life and past and possibilities were those of other people, or that they should consist in incompatible elements, it's also sinful to complacently accept my life, past and present, as completely good, necessary, unchangeable, and perfectly willable, even though this isn't true. Instead I must recognize what is possible but not actual for myself, past present and future, allowing the necessary room for repentance about the past, effort in the present, and resolutions about the future.