Abstract

Evolutionary debunking arguments use the evolutionary origins of our moral attitudes to argue that our moral beliefs are not explained by realistically construed moral facts, and that our moral beliefs are therefore unjustified. Third-factor replies to debunking argument rely on substantive moral claims to argue that, even if our moral beliefs are not explained moral facts, they are explained by some third-factor that also explains those moral facts. This is supposed to show that our moral beliefs can be justified even given the debunker’s evolutionary genealogy of those beliefs. In this paper I argue that third-factor replies fail. First, I argue that our belief is defeated if we withhold belief that it is explained by the fact that makes it true or by some third-factor that also explains that fact. I then argue that the third-factor replier cannot consistently take our beliefs about basic moral principles to be explained by some such third-factor because of the concession they make in response to debunking arguments and the meta-ethical view they are looking to defend. This implies that the third-factor replier’s beliefs about basic moral principles are defeated. Furthermore, we cannot take non-basic moral beliefs to be explained by some such third-factor if we withhold our basic moral beliefs, and so the third-factor replier’s non-basic moral beliefs are also defeated. Thus, the third-factor replier ought to withhold their moral beliefs in response to debunking arguments and, because their arguments rely crucially on moral claims, those arguments fail.