  The last objection to moral naturalism that we will consider is the Motivation Objection. This objection is a favorite of metaethical expressivists, and they deploy it with equal fervor against all moral realists, both naturalists and non-naturalists alike. But it is still worthy of discussion as a major objection to naturalist moral realism, because naturalism is the realist view that seems to have the most problem answering the objection.