Why Companions in Guilt Arguments Won't Work

One recently popular strategy for avoiding the moral error theory is via a 'companions in guilt' argument. I focus on those recently popular arguments that take epistemic facts as a companion in guilt for moral facts. I claim that there is an internal tension between the two main premises of these arguments. It is a consequence of this that either the soundness or the dialectical force of the companions in guilt argument is undermined. I defend this claim via (i) analogy with philosophical debates concerning the indispensability of mathematical objects to natural science, and (ii) discussion of the 'entanglement' of epistemic concepts and moral concepts in deliberation. I conclude by proposing a positive view of what kind of argument must be used if moral error theories are to be successfully undermined.