Date of Degree


Document Type


Degree Name





Jesse Prinz

Committee Members

Hagop Sarkissian

Catherine Wilson

Subject Categories

Ethics and Political Philosophy | Philosophy | Philosophy of Language | Philosophy of Mind | Philosophy of Science


Ethics, Moral Philosophy, Metaethics, Moral Realism, Moral Psychology


Morality is not merely a social construction or a convenient fiction. Nor is it supernatural or non- natural. Rather, ethics could eventually be studied as a branch of the social sciences, concerned with empirically discovering the many and diverse best ways of living. There are moral facts (like “murder is wrong”), and these facts are natural, objective, and universal. In other words, moral realism is true.

Philosophers often assume that moral realism matters because it is a commitment of common sense. Drawing on new work in the psychology of metaethics, I argue that ordinary people are not in fact moral realists. Instead, in the absence of principled philosophical education, or religious indoctrination, the folk have highly variable metaethical attitudes. I explain this folk metaethical pluralism by arguing that metaethical attitudes are seldom caused by rational processes, but instead are typically the result of a variety of developmental, social, personality, and judgment factors, all rationally irrelevant to the truth of moral realism.

If moral realism is not a commitment of common sense, then some may doubt that moral realism matters at all. I argue for a new reason to think that this thesis matters: when we believe it, it can make us more moral. New empirical findings show that people who have objectivist and universalist attitudes toward their own morality are more likely to act in accordance with that morality. Though this may not be good from an outside, objective perspective, it is good from the perspective of virtually every person’s subjective system of moral beliefs. This gives us a strong moral reason to be moral realists.

Moral realism has more than moral goodness to recommend it, however. We can epistemically secure objectivity in ethics by understanding moral facts from a metaphysical perspective that is simultaneously reductionist and realist. I formulate a metaphysical relation that I call thin reductionism, which is a minimal metaphysical relation between facts. I argue that every fact must have this relation with some other set of facts if that fact is to be even minimally scientifically respectable. I then argue that we have reason to believe that moral facts are no special case, and that we ought to therefore reject non- naturalist interpretations of ethics. If moral facts exist at all, they must be identical to some subset of natural facts. I also respond to conceptual objections to ethical reductionism, including Hume’s is/ought gap, Moore’s open question argument, and Moral Twin Earth. All of these, I claim, rely on false assumptions about how we can come to know the meaning of moral concepts. Though philosophers often think we can, no one can simply intuit the meaning of our moral concepts. As a result, proper account of moral semantics cannot be determined without a normative ethical theory that answers to global epistemic considerations.

If there is a naturalistic account of the metaphysics of morals, this provides a powerful way to respond to classic arguments against the possibility of objectivity in ethics. Because many of the metaphysical and epistemic arguments against the objectivity of morality are premised on the idea that moral facts must be somehow metaphysically or epistemically special, these arguments fail if it turns out that moral facts aren’t special at all. I respond to the major arguments in this vein, including supervenience, explanation, and evolutionary skepticism.

Even if morality is natural and objective, this does not imply that it is universal. Nevertheless, I argue that a portion of folk morality really is universal, and that metaethics and psychology can define the outer limits of a naturalistic, objective, and universal morality. I draw on the empirical literature on moral judgment to show that the foundational content of moral judgments is produced by innate cognitive modules and is shared cross-culturally. I then show how this innateness and universality can bolster a traditional response to the argument from disagreement. We can eliminate fundamental moral disagreements by using a targeted argument from disagreement, which undermines the more controversial and unnaturalizable binding foundations of moral judgment, while sparing the universally shared and more readily naturalizable individualizing foundations. This gives us reason to believe that a portion of folk morality is innate, and tracks natural facts that are objective and universal, while another portion of folk morality is innate, but fails to track anything real. This conclusion has implications for normative ethics, since the portion of morality that tracks these natural, objective, and universal moral facts broadly corresponds with liberal, enlightenment values concerning harm reduction and justice.