Possible or ideal psychology may permit more demanding moral motivations than actual psychology.

This worry about the demands of utilitarianism is not easy to assess. One might wonder how to interpret and whether to accept the psychological realist constraint. If the constraint is relative to people’s actual psychologies, then it represents a potentially conservative constraint on moral theorizing that one might well reject. If the constraint is relative to possible or ideal psychology, then it is not clear that even a highly revisionary moral theory need flout the constraint. Then there is