What Is Moral Non-Naturalism? Definition & Arguments

Direct Answer

Moral non-naturalism is the metaethical theory that moral properties are not natural properties and cannot be defined in natural terms. Its most famous defender is G.E. Moore, who argued in Principia Ethica (1903) that "good" is a simple, unanalyzable, non-natural property. "Simple" means it cannot be broken down into parts; "unanalyzable" means it cannot be defined; "non-natural" means it is not the kind of property studied by the natural sciences. Goodness is real and objective — non-naturalism is a form of moral realism — but it is sui generis, of its own kind, irreducible to pleasure, desire, well-being, evolutionary function, or any other natural fact. The theory says that when we call something good, we attribute to it a genuine property, and our claim is true or false depending on whether the object really has that property. Because the property is non-natural, moral truths cannot be discovered by empirical science; they are known, Moore argued, by intuition — a position that makes non-naturalism the natural ally of intuitionism.

Historical Context

Non-naturalism emerged from the collapse of the idealist moral philosophy that dominated late-nineteenth-century Britain. Henry Sidgwick, in The Methods of Ethics (1874), had already insisted on the indefinability of moral terms and the intuitional character of basic moral axioms, preparing the ground. It was Moore, however, who turned this into a systematic metaethical theory. Reacting against both the utilitarian naturalism that identified the good with pleasure and the idealist metaphysics of his teachers, Moore argued in Principia Ethica that philosophers had repeatedly confused two distinct questions: "What things are good?" — a normative question about what has value — and "What does 'good' mean?" — a metaethical question about the nature of the property itself. Moore's answer to the second question — that "good" is indefinable and non-natural — defined the agenda for twentieth-century metaethics. For most of the century, non-naturalism was treated with suspicion, especially by naturalists and logical empiricists, but it experienced a revival in the late twentieth century through the work of Derek Parfit and others who sought to defend objective value against the tide of anti-realism.

Key Arguments & Debates

The central argument for non-naturalism is the open-question argument. Moore asked us to consider any proposed definition of the good, for example "the good is pleasure." We can then ask: "This act is pleasant, but is it good?" The question is meaningful and open — it does not answer itself the way "this is a bachelor, but is he unmarried?" does. Moore concluded that "good" cannot be identical with pleasure (or with any natural property), because if the two were identical, the question would be closed. The argument has been criticized from many angles: naturalists reply that the openness only reflects a gap in our concepts, not in reality, and that identity statements such as "water is H2O" were similarly open before science discovered them. Non-naturalists must also answer the supervenience question: moral properties supervene on natural properties, so how can they be non-natural? And the epistemological question: if moral properties are non-natural, how do we come to know them? Critics such as J.L. Mackie pressed these worries — the "queerness" of non-natural properties and the mysterious faculty of intuition that would be needed to grasp them. Contemporary non-naturalists respond that normative knowledge is a legitimate form of non-empirical knowledge, as mathematical knowledge is.

Contemporary Relevance

Non-naturalism matters today because it is the clearest statement of the view that moral truths are objective yet not reducible to facts about biology, psychology, or social convention. This position underlies a great deal of ordinary moral thinking: many people believe that human rights are not merely useful inventions but are true in a way that no scientific discovery could overturn. The theory also anchors the realism debate: if naturalism is a realist strategy that grounds value in the natural world, non-naturalism is the realist strategy that defends value as autonomous. Contemporary philosophers such as Derek Parfit and T.M. Scanlon have revived versions of non-naturalism (Scanlon's is constructivist) in response to the perceived failures of both naturalism and anti-realism, making the theory central to current debates about reasons, values, and normativity.

Related Concepts

Non-naturalism is best understood against moral naturalism, its great rival within realism. The naturalistic fallacy is the mistake — identified by Moore — of identifying goodness with a natural property, and the open-question argument is its engine. Non-naturalism is typically paired with moral intuitionism, since Moore held that non-natural truths are known by intuition, and it participates in the general debate over moral realism and anti-realism.

Further Learning

The Stanford Encyclopedia of Philosophy entry on moral non-naturalism is the definitive survey. For Moore's own argument, read Principia Ethica (Cambridge University Press, 1903); for the revival, see Derek Parfit's On What Matters (Oxford University Press, 2011). A concise overview of the surrounding debate is available in the Internet Encyclopedia of Philosophy's entry on G.E. Moore.