Naturalistic fallacy

The naturalistic fallacy is a central concept in metaethics, describing the mistaken attempt to define the evaluative property good in terms of purely natural, descriptive properties such as pleasant, desirable or biologically fit. Introduced by the British philosopher G. E. Moore in Principia Ethica (1903), the term is closely connected to broader debates on the relationship between facts and values, especially the issue of deriving an ought from an is. While inspired by David Hume’s discussion of fact–value distinctions, Moore’s concept serves a distinct purpose within ethical non-naturalism.

The Is–Ought Problem and Common Usage

In everyday discussions, the naturalistic fallacy is often taken to refer to the is–ought problem—the faulty inference that because something is the case, it ought to be the case. This can take the form of appealing to widespread behaviour as moral justification. Related inferences appear frequently in discussions of natural law, social customs or biological tendencies.
The appeal commonly follows a pattern in which descriptive facts are invoked as if they entail normative conclusions. For example, because people naturally act in certain ways, it is argued that these behaviours are morally good. Moore regarded such attempts as philosophically unsound, though his primary concern was narrower than general fact–value reasoning.

Moore’s Argument and Ethical Nonnaturalism

Moore’s naturalistic fallacy concerns the semantic and metaphysical analysis of moral terms. He argued that good is a simple, indefinable quality that cannot be reduced to natural properties such as pleasure or desirable outcomes. According to Moore, attempts to equate good with any natural feature fail the open question argument: for any proposed definition, it remains an open question whether that natural property is in fact good.
For Moore, simple terms such as colour qualia illustrate indefinability; understanding a simple property like yellow is achieved by direct acquaintance, not by definition. In the same way, understanding goodness does not arise from analysing descriptive features. Thus, ethical naturalism—attempts to define moral properties in scientific or psychological terms—is rejected, while moral realism may still be maintained.

Appeal to Nature in Ethical Reasoning

The phrase naturalistic fallacy is sometimes used in a broader, informal sense to criticise arguments that appeal to nature for moral justification. Such arguments assert that because something is natural it is morally acceptable, or that what is unnatural must be undesirable. These inferences are common in discussions of health, environmental ethics, sexuality or dietary debates. Although this usage diverges from Moore’s technical meaning, it illustrates a persistent error in moral reasoning.

Criticisms and Alternative Approaches

Moore’s formulation has been criticised from several angles. Bernard Williams described the term as misleading, since Moore’s argument is conceptual rather than strictly logical. Some philosophers argue that the is–ought distinction is not as firm as commonly assumed. The claim that ought is embedded within is suggests that the functions or natures of things produce evaluative standards: understanding what something is includes understanding what it should do.
Other critics challenge the notion that empirical facts and moral norms are disconnected. They argue that moral judgements arise within cognitive processes shaped by factual beliefs. Differences in perceived facts can lead individuals to different moral conclusions, illustrating the complex interaction between descriptive and normative dimensions.

Inconsistent Application and Rhetorical Use

Some commentators note that accusations of the naturalistic fallacy are often applied inconsistently. For example, critics of evolutionary psychology sometimes argue that it commits the fallacy, while simultaneously making evaluative claims about the consequences of certain beliefs or behaviours. This inconsistency suggests that the label is sometimes used rhetorically rather than diagnostically.
Furthermore, discussions of harm or social consequences exhibit how descriptive claims may carry implicit normative weight. Depending on the values held, descriptions of groups or behaviours can have different moral implications. This underscores the difficulty of maintaining a strict separation between factual statements and moral interpretation.

Broader Implications in Metaethical Debate

The naturalistic fallacy remains a significant topic in metaethical theory. It raises questions about the nature of moral properties, the role of intuition in ethical understanding and the limits of empirical approaches to ethics. While many philosophers continue to accept a distinction between descriptive facts and normative values, others explore ways in which evaluative concepts may be grounded in human psychology, social practices or naturalistic accounts of moral reasoning.