What Is Moral Naturalism? Definition & Theories

Question

What is moral naturalism, and how could moral truths be part of the natural world? The question is central to meta-ethics: it asks whether the good can be understood in the same terms as the rest of reality, or whether the values stand apart from the facts.

Quick Answer

Moral naturalism is the metaethical theory that moral properties are natural properties and that moral truths are part of the natural world, knowable by the same empirical and rational methods as the truths of the sciences. The naturalist holds that "good" and "right" refer to natural facts — facts about well-being, flourishing, desire-satisfaction, or human nature — and that the moral judgment "X is good" is true in virtue of the natural facts about X. The theory is a form of moral realism: moral truths exist, and they are objective, because they are truths about the natural world. Its great obstacle is the is-ought problem, posed by Hume: how can the normative "ought" be derived from the descriptive "is"? The naturalist answers that the distinction is not as sharp as Hume suggested — the facts about human nature and well-being carry normative weight — and that moral knowledge is continuous with natural knowledge. The great rival of naturalism is the non-naturalism of G.E. Moore, who argued in Principia Ethica (1903) that "good" is a simple, non-natural property that cannot be defined in natural terms, and that the attempt to define it commits the naturalistic fallacy.

Historical Wisdom

Moral naturalism has deep roots. Aristotle grounded the ethics in the natural teleology of the human being: the good life is the life of the flourishing human being, and the virtues are the characteristics that enable the flourishing — the ethics is the natural knowledge of the human good. The modern naturalism was developed by the utilitarians: Bentham defined the good as the pleasure, and Mill as the happiness — natural facts, measurable by the empirical methods. The theory was challenged by Moore in 1903: his open-question argument — "is the good the pleasure? the question remains open, therefore the good is not the pleasure" — seemed to show that the good cannot be defined in natural terms, and the naturalism went into decline. The twentieth century revived it: the Cornell realists (Boyd, Brink, Railton) argued that the moral terms refer to natural kinds, as "water" refers to H2O, and that the moral truths are the natural truths discovered by the empirical investigation of human nature and well-being.

Philosophical Perspectives

Moral naturalism has three components. The ontological claim: moral properties are natural properties — the goodness is a natural fact about the world, not a non-natural or supernatural property. The semantic claim: the moral terms refer to the natural properties — "good" refers to the property (well-being, flourishing, desire-satisfaction) that the theory identifies. The epistemological claim: moral truths are knowable by the natural methods — the same observation, theory, and reasoning by which the truths of the sciences are known. The theory is the most ambitious form of moral realism: it promises the objectivity of the moral truths without the metaphysics of the non-natural.

The great obstacle is the is-ought problem. Hume observed that the moral arguments move from the "is" of the facts to the "ought" of the values without explanation, and the non-naturalists concluded that the gap is unbridgeable. The naturalist answers in two ways. The first is the rejection of the sharp distinction: the descriptions of the human nature and the human well-being are not purely descriptive — the fact that the child flourishes with the care and withers without it is a fact that carries normative weight. The second is the natural-kind response: the moral terms refer to natural properties as "water" refers to H2O — the discovery that the good is the well-being is the discovery of the identity, not the reduction of the value to the fact.

Lessons From Thinkers

From Aristotle: the ground — the good life is the flourishing of the human being, and the ethics is the natural knowledge. From G.E. Moore: the challenge — the open-question argument, and the naturalistic fallacy. From Bernard Williams: the caution — the naturalistic account must not lose the texture of the moral life, the thick concepts that carry the real moral substance.

Practical Application

Moral naturalism has direct practical application. For the person: the theory grounds the moral convictions in the facts — the conviction that the cruelty is wrong is grounded in the facts about the harm and the flourishing, and the moral reasoning is continuous with the reasoning about the human good. For the public debate: the naturalism supplies the common ground — the arguments about the rights, the welfare, and the justice are arguments about the facts of the human well-being, and the empirical evidence is relevant to the moral conclusions. For the student of the ethics: the is-ought problem is the reminder of the difficulty — the derivation of the value from the fact is the deepest question of the meta-ethics, and the naturalist must answer it with the care that the subject demands.

Quotes

Hume poses the problem: "In every system of morality, I have always remarked that the author proceeds for some time in the ordinary way of reasoning... when of a sudden I am surprised to find that instead of the usual copulations of propositions, is and is not, I meet with no proposition that is not connected with an ought or an ought not." Moore states the challenge: "The good is a simple, non-natural property, and the attempt to define it in natural terms commits the naturalistic fallacy." And the naturalist's answer: "The moral truths are the natural truths about the human well-being — the facts carry the values, and the values are knowable by the natural methods."

Related Questions

• What Is the Is-Ought Problem? — the great obstacle.
• What Is Meta-Ethics? — the wider field.
• What Is Moral Realism? — the realism that naturalism defends.
• Moral Relativism vs Absolutism — the objectivity debate.