I’ve explained it many times. I don’t know how much clearer I can be, or even what it is you disagree with, but I’ll try once more:
- A soldier has an obligation to salute his superior officer because that is the institutional norm
- A soldier has a moral obligation to salute his superior officer because that is the institutional norm
Whatever the word “moral” means, either (1) and (2) mean the same thing and have the same truth value or they don’t mean the same thing and can have different truth values. So one of these must be true: a) (1) is false, b) (2) is true, or c) there are non-moral obligations.
Which of (a), (b), or (c) is your position? Mine is (c) because (1) and (2) do not prima facie mean the same thing; (1) seems uncontroversially true but (2) is an open question — and both the realist and the nihilist will argue that (2) is false because moral obligations are not the sort of thing that can be established by institutional norms (contra the relativist).