Cornell realists maintain that irreducible moral properties have earned a place in our ontology in virtue of the indispensable role they play in a variety of explanations. These explanations can be divided into two groups: those that employ thin ethical concepts and those that employ thick ethical concepts. Recent work on thick concepts suggests that they are not inherently evaluative in their meaning. If correct, this creates problems for the moral explanations of Cornell realists, since the most persuasive moral explanations are those that employ thick concepts. If thick concepts are not inherently evaluative, then the most plausible explanations on offer cannot support Cornell realism. Moral explanations employing thin concepts, however, are too flimsy to support the view. Unless proponents can develop a compelling story about thick concepts or thin explanations, Cornell realism is in trouble.