When I say that something is metaphysically impossible to do, I will mean: metaphysically impossible for creaturely causation. For this post I leave open the question of what God might be able to do through primary causation. The following seems quite plausible to me:
- If a particle is in a mixed |A>+|B> quantum state, then it is metaphysically impossible to determine the particle to collapse into the |A> state.
The following seems to me to be just as plausible as (1):
- If an agent is deciding between A for reasons R and B for reasons S, then it is metaphysically impossible to determine the agent to choose A for R over B for S.
Simply doing A after deciding between A and B does not constitute having chosen A. Nor is it sufficient for having chosen A that one does A because of deciding between A and B. For one to have chosen, one's doing of A must be caused in the right way by one's process of decision between A for R and B for S. But it just seems very implausible that an externally determined transition, even if it somehow causally incorporated the process of decision, would be a case of causing in the right way.
Could there perhaps be overdetermination, so that one's transition from deciding between A and B one's doing of A be both an exercise of freedom and externally determined? Quite possibly. But that wouldn't be a case where the choice is overdetermined. Rather, it would be a case where choice and external determination overdetermine the action A. The choice, however, is still un-determined.
But couldn't one make the agent choose A for R over B for S by strengthening the motive force of R or weakening that of S? I don't think so. For as long as each set of reasons has some motive force over and against the other set of reasons, it might yet win, just as a particular in a |A>+0.000001|B> state might yet collapse into the |B> state.
The above doesn't settle one question. While it is not possible to determine that one choose A over B, maybe it is possible to determine that one not choose B, by preventing a choice into a decided-for-B state, while allowing a choice in favor of the decided-for-A state? I see little reason to allow such a possibility.