The Open Question Argument
Whatever natural property you say 'good' means, whether pleasure, survival, or flourishing, it always makes sense to ask: but is that property actually good? If so, what does 'good' really mean?
G. E. Moore published this argument in 1903 as a challenge to ethical naturalism, the project of defining moral terms using natural or scientific concepts. If 'good' can always be coherently questioned when identified with any natural property, Moore argued, it cannot be defined in natural terms at all.
Moore, G. E. (1903). Principia Ethica. Cambridge University Press.
The argument, with a concrete example
Suppose you're a hedonist. You believe that "good" means pleasure. On this view, "pleasure is good" is a tautology, like "a bachelor is unmarried." You can't meaningfully doubt it.
But Moore points out: you can ask, without any confusion, "Yes, this is pleasurable, but is it actually good?" That question is not like asking "Is a bachelor really unmarried?" It feels open. It has genuine content. People disagree about the answer.
The same test applies to any natural property. Evolutionary ethicists say "good" means what promotes survival and reproduction. Ask: "But is promoting survival actually good?" The question makes sense. Theological naturalists say "good" means what God commands. Ask: "But is what God commands actually good?" Same result. The question never closes.
Moore concluded that if "good" were identical to any natural property, these questions would be as nonsensical as "Is a bachelor really unmarried?" The fact that they remain open proves the identity is false. He called the mistake of treating "good" as definable in natural terms the naturalistic fallacy.
The naturalistic fallacy
Moore was targeting a widespread move in Victorian ethics: deriving moral conclusions from facts about nature, evolution, pleasure, or divine command. This move, he argued, is always a sleight of hand.
The naturalistic fallacy is the error of defining ethical terms using non-ethical terms. Not just any error in moral reasoning, but specifically this one: treating "X is good" as if it were equivalent to "X has natural property Y."
The argument has teeth beyond metaethics. It challenges any attempt to ground morality in science, evolution, or religion in a straightforward way. Even if it's true that humans evolved to value cooperation, the question "But is cooperation good?" remains genuinely open. The fact can't settle the value.
The objection
The most persistent objection: maybe "good" is just harder to define than "bachelor," not indefinable.
Definitions of complex terms take work. "Knowledge" took philosophers centuries to partially define, and debates continue. That doesn't make knowledge an unanalyzable simple. Maybe "good" is similar: our current definitions fail, but that's a problem about our analysis, not about the nature of the concept.
Moore anticipated this. His response is that the open question isn't a symptom of definitional difficulty in the way "What is knowledge?" is. When someone genuinely asks "Is pleasure good?" they are not asking for clarification of the concept of pleasure. They're asking a further question. The structure of the question is different, which is evidence that the concepts are not identical.
Whether that evidence is decisive is what the argument leaves open.
Discussion questions
- Is 'is X good?' always a meaningful question, no matter what X is?
- What do you think 'good' means, and does Moore's argument make you doubt your answer?
- Does it feel right to you that 'good' cannot be boiled down to any simpler concept, or does that feel like a gap in the argument?
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