 In general, the worry about Joyce’s debunking argument is similar to the worry about Street’s: unless we start out already assuming (against the realist) that there are no knowable moral truths, it is hard to see why we should accept Joyce’s premise that we possess a complete non-moral geneaology of moral judgment, and hence that it is explanatorily superfluous to posit moral truths. Whether or not the non-moral geneaology is complete is precisely what is in question in ongoing metaethical debates: realists, who posit knowable moral truths, can reasonably hold that the correct explanation for at least many of our moral beliefs does appeal to moral truths or facts that we have grasped, while anti-realists, who deny the existence of such truths, claim that the correct explanation for all of our moral beliefs involves no such appeal. The issue remains controversial. So unless one has independently settled that issue against realism, one is unlikely to accept the premise that there is a complete non-moral genealogy of our moral beliefs: there may well be a partial non-moral genealogy, for the sorts of reasons Joyce gives, but it will be complete only if none of our moral beliefs are the result of our having grasped moral truths; and this negative claim will be very unlikely if there are in fact knowable moral truths (since we would plausibly have grasped some of them, and they would thus figure into the explanation of some of our moral beliefs). We should therefore feel compelled to grant Joyce’s premise that there is such a complete non-moral genealogy only if we have already given up on the idea of knowable moral truths. But that makes it hard to see how the argument as a whole can be used to persuade anyone who doesn’t already accept its conclusion.