So if an empty moral system is rational, and that's the only one we have, isn't that the same as saying there is no rational moral system? I agree that you wan

So if an empty moral system is rational, and that's the only one we have, isn't that the same as saying there is no rational moral system? I agree that you want to minimise axioms, but not because they're a source for error - after all, the concept of "valid" flows entirely from not violating the axioms - but because internal consistency leans on axioms not contradicting each other. That might have been what you meant though, in which case we're in agreement.