Why defining "good" as anything physical always leaves an open question
If "good" simply meant "causing pleasure," asking whether a pleasurable act is good would be as silly as asking if an unmarried man is a bachelor. In 1903, G.E. Moore pointed out that for any natural definition—like pleasure or evolutionary survival—we can still meaningfully ask: "Yes, but is it good?" Because that question always stays open, Moore argued goodness cannot be reduced to physical facts.
The Search for the Meaning of Good
For centuries, philosophers attempting to ground morality sought to anchor the concept of 'good' in something observable in the natural world. Utilitarians suggested that goodness is simply the maximization of pleasure and the minimization of pain. Evolutionary thinkers argued that moral goodness reflects behaviors that promote species survival and social cohesion. Others pointed to psychological fulfillment, human desire, or societal harmony. In each case, thinkers attempted to take an abstract, elusive moral term and define it cleanly using physical, psychological, or biological facts.
In his 1903 work Principia Ethica, the English philosopher George Edward Moore interrupted this long tradition. Moore argued that every single attempt to define 'good' in terms of natural properties rests on a fundamental mistake. To demonstrate this, he introduced what became known as the Open Question Argument, a deceptively simple test designed to show that moral goodness cannot be identical to any physical or natural quality.
How the Open Question Argument Works
Moore’s test relies on a distinction between 'closed' and 'open' questions. A closed question is one whose answer is settled by the very definitions of the words involved. If someone asks, 'I know John is an unmarried man, but is he a bachelor?', the question is conceptually trivial. To understand the word 'bachelor' is already to know that he is one. Denying it or asking for further proof reveals a linguistic misunderstanding rather than a genuine factual or moral inquiry.
An open question, by contrast, remains meaningful and intelligible even after all the definitions are understood. Moore invited readers to test any proposed natural definition of goodness against this distinction. If a philosopher claims that 'good' literally means 'causing pleasure,' then asking 'This act causes pleasure, but is it good?' should sound as nonsensical and redundant as asking if a bachelor is unmarried. Yet the question never sounds nonsensical. It remains completely intelligible, open to debate, and substantive.
Because one can always meaningfully ask whether a pleasurable act, an evolutionary adaptation, or a fulfilled desire is actually good, Moore argued that goodness cannot simply be identical to pleasure, survival, or desire. The question stays open because the concept of goodness is distinct from whatever natural features accompany it.
The Naturalistic Fallacy and Simple Properties
Moore termed the error of identifying moral properties with physical ones the 'naturalistic fallacy.' In his view, naturalists conflate the things that possess goodness with goodness itself. An apple may be round and sweet, but roundness is not sweetness; similarly, an action may be pleasurable and good, but pleasure is not goodness.
To explain what goodness actually is, Moore drew a famous comparison to the color yellow. If a person who has never seen color asks what yellow is, no physical explanation can fully define the visual quality itself. One can describe the wavelengths of light that produce it or list yellow objects like lemons and daffodils, but the qualitative experience of 'yellow' is a simple, unanalyzable property. It cannot be broken down into smaller constituent concepts.
Goodness, Moore argued, is similarly simple and unanalyzable. Unlike complex concepts such as 'horse'—which can be broken down into parts like four legs, a mane, and specific anatomy—good is a basic building block of reality. It can be recognized, but it cannot be disassembled into non-moral components through definition.
Moral Non-Naturalism and Intuition
Moore’s conclusion led him to endorse moral non-naturalism: the view that moral properties exist, but they are not physical, empirical, or reducible to the entities studied by the natural sciences. Goodness is a real feature of states of affairs, but it belongs to a non-natural category of properties.
If goodness cannot be detected through sensory observation, scientific measurement, or definitional breakdown, a central epistemological question arises: how do humans know what is good? Moore’s answer was a form of ethical intuitionism. He held that foundational moral truths are self-evident to rational reflection. While we use empirical observation to learn the physical consequences of an action, the realization that a particular outcome or state of mind is inherently good is an act of direct intellectual awareness.
The Meaning Versus Reference Critique
Despite its enormous influence, the Open Question Argument faced major challenges in the latter half of the twentieth century. The primary objection emerged from developments in the philosophy of language, specifically the distinction between the meaning of a concept and the real-world property to which it refers.
Consider the discovery that water is chemically composed of two hydrogen atoms and one oxygen atom. Before modern chemistry, the question 'I know this liquid is water, but is it H2O?' was an open, intelligible question. It was not a conceptual contradiction to doubt it. Yet science proved that water is, in fact, identical to H2O. The two terms have different conceptual meanings (senses), but they refer to the exact same physical substance.
Critics applied this insight to ethics. Even if 'good' and 'maximizing pleasure' do not mean the same thing conceptually—explaining why the question feels open—goodness and pleasure might still refer to the same underlying natural property in the world. From this perspective, Moore proved that 'good' cannot be analytically defined away, but he did not necessarily prove that goodness is a mysterious, non-physical phenomenon.
The Legacy in Metaethics
Moore’s argument fundamentally reshaped modern philosophy by shifting attention from normative ethics—asking which acts are right—to metaethics, the systematic study of what moral terms mean and what kind of reality moral claims describe. Principia Ethica established the standard that any naturalistic account of morality must explain why moral judgments feel distinct from purely descriptive statements.
Whether philosophers agree with Moore's non-naturalism or side with modern physicalist critiques, the Open Question Argument remains a central touchstone. It clearly highlighted the persistent gap between purely descriptive descriptions of the world—what is—and the evaluative judgments we make about it—what ought to be.
Key takeaways
•Moore's Open Question Argument demonstrates that for any physical definition of 'good' (such as pleasure or survival), asking whether that physical quality is actually good remains a meaningful, open question.
•If 'good' were identical by definition to a natural property, questioning whether that property is good would be a nonsensical tautology, similar to asking if an unmarried man is a bachelor.
•Moore concluded that goodness is a simple, unanalyzable, non-natural property—comparable to the color yellow—that cannot be broken down into physical components.
•Later critics argued that Moore showed a difference in linguistic meaning rather than metaphysical reality, pointing out that two concepts can have different meanings while still referring to the same underlying physical property (like water and H2O).