This essay proposes and defends a descriptive definition of morality.Under this definition, a moral system is a system of rules, psychological states,and modes of character development which performs the function of enabling mutually beneficial social cooperation.I shall argue that the methodologies employed by two prominent moral psychologists rely upon to establish a descriptive definition of morality only serve to track patterns in people’s uses of moral terms.However,these methods at best reveal a nominal definition of morality, since moral appraisers may be ignorant about the references of their moral terms.I propose a real definition of morality which characterizes moral systems as a natural kind—more precisely, a copied kind. I explain what it takes for a moral system to satisfy this definition, and I identify the sorts of evidence needed to distinguish moral systems from value systems of other kinds.