The Significance of Significant Fundamental Moral Disagreement1

This paper has four parts. In the first part I argue that moral facts are subject to a certain epistemic accessibility requirement. Namely, moral facts must be accessible to some possible agent. In the second part I show that because this accessibility requirement on moral facts holds, there is a route from facts about the moral disagreements of agents in idealized conditions to conclusions about what moral facts there are. In the third part I build on this route to show that if there is significant moral disagreement in idealized conditions, then our understanding of morality is fatally flawed and we should accept relativism over non-naturalism and quasi-realism. So, if, like many, you think that there would be significant moral disagreement in idealized conditions, you should hold that our understanding of morality is fatally flawed and reject non-naturalism and quasi-realism. In the fourth part of this paper I show that undermines the plausibility of non-naturalism, quasi-realism, and the view that our understanding of morality is not fatally flawed even if we do not have sufficient reason to believe that there would be significant moral disagreement in idealized conditions.