A friend and I were talking about the recent blog post and the "ought implies can" principle. We agreed that we should make the principle explicit in a somewhat philosophical form, so here goes:
S is morally obligated to do X at t if and only if S is commanded to do X at t and it is within S's causal power to do X at t in the actual world.
This formulation prevents against the idea that whatever one can do, one ought to do (hence the "command" clause). It also helps avoid problems that arise when it is possible for S to perform X at t in one sense, but not in another. For instance, if S is commanded to fly (without any aids) it is logically (and even metaphysically) possible for S to fly; yet, if S is a human, S cannot perform this act. In fact, it is physically impossible for S to fly, so that it is not within S's causal power to fly at time t. So, if someone could possibly perform some morally-commanded action in the actual world, then they have an obligation to do such. If, however (per impossible, as I happen to think), S is morally-commanded to do some action at a time that lies outside of her causal power in the actual world at that time, then S would not be morally obligated to do such a thing at that time.
H/T to Pranav Bethala. Although, I wouldn't tip my hat even if I had one, so perhaps we can change it to "hat throw"?
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