So, “You can do what you should do” is equivalent to”You should do what you should do”.
If these are equivalent, then the truth of the second statement should entail the truth of the first. But “You should do what you should do” is ostensibly a tautology, while “You can do what you should do” is not, and could be false.
One out you might want to take is to declare “S should X” only meaningful when ability and circumstance allow S to do X; when “S can X.” But then you just have two clear tautologies, and declaring them equivalent is not suggestive of much at all.
As you have shown them to not be equivalent, I would have done better to say:
“You can do what you should do” entails “You should do what you should do”.
But if the latter statement is truly a tautology, that obviously doesn’t help. If I then add your second edit, that by “should” I mean “provided one is able to”, I am at least less wrong...but can my argument avoid being wrong only by being vacuous?
If these are equivalent, then the truth of the second statement should entail the truth of the first. But “You should do what you should do” is ostensibly a tautology, while “You can do what you should do” is not, and could be false.
One out you might want to take is to declare “S should X” only meaningful when ability and circumstance allow S to do X; when “S can X.” But then you just have two clear tautologies, and declaring them equivalent is not suggestive of much at all.
Decisive points.
As you have shown them to not be equivalent, I would have done better to say:
But if the latter statement is truly a tautology, that obviously doesn’t help. If I then add your second edit, that by “should” I mean “provided one is able to”, I am at least less wrong...but can my argument avoid being wrong only by being vacuous?
I think so.