Premise (2) of the argument is taken as given by those who advance this argument, but of course some would deny it. Premise (1) might seem strange, since we have substantive knowledge of many kinds of facts that surely are mind-independent, such as facts about the stars. But (1) is intended as a claim specifically about knowledge of normative facts. The claim is that there is something about the normative such that we could not have knowledge of facts of this kind if they were mind-independen