Principia Ethica

Context

Principia Ethica, published in 1903 by Cambridge University Press, is the foundational text of twentieth-century metaethics and one of the most influential works of analytic philosophy ever written. Its author, George Edward Moore, was then a young Fellow of Trinity College, Cambridge, and a central figure in the intellectual ferment that was transforming British philosophy at the turn of the century. Together with his close friend and colleague Bertrand Russell, Moore was leading a revolt against the idealist philosophy that had dominated British universities for a generation — the absolute idealism of F.H. Bradley and T.H. Green, which held that reality is a single, all-inclusive, spiritual whole and that ordinary moral distinctions are ultimately illusory.

The idealism against which Moore and Russell rebelled was not merely a philosophical position but an academic establishment. The professorships at Oxford and Cambridge were held by idealists, the textbooks were written by idealists, and the intellectual atmosphere was one in which common sense and clear reasoning were regarded as philosophically naive. Moore's rebellion was motivated by a deep conviction that the deliverances of common sense — that tables exist, that some things are good and others bad, that we can know truths about the world — were more trustworthy than the elaborate metaphysical systems that denied them. Principia Ethica was, among other things, a manifesto for this conviction: an attempt to bring the same clarity, rigor, and respect for common sense to moral philosophy that Russell was bringing to logic and the philosophy of mathematics.

But Principia Ethica was not merely a negative work — not merely a demolition of idealism. It was also a constructive attempt to answer the most fundamental question in ethics: what is good? Moore's answer was as radical as it was simple. "Good" is the name of a simple, unanalyzable, non-natural property — a property that cannot be reduced to any natural property (pleasure, happiness, desire-satisfaction) and cannot be defined in terms of anything else. It is, Moore argued, as impossible to define "good" as it is to define "yellow." You can point to examples of yellow things, but you cannot tell someone who has never seen yellow what yellowness is. Similarly, you can point to examples of good things, but you cannot tell someone who has never grasped the concept of goodness what goodness is. It is a fundamental concept, irreducible to anything more basic.

This position — that "good" is a simple, non-natural property — places Moore in a tradition known as ethical non-naturalism. It stands in opposition to ethical naturalism, which holds that "good" can be defined in terms of natural properties (John Stuart Mill defined good as pleasurable; Aristotle defined good as that which fulfills a thing's nature). It also stands in opposition to ethical non-cognitivism, which holds that "good" doesn't refer to a property at all but merely expresses an attitude or prescription (A.J. Ayer would later argue that "x is good" means "hurrah for x!"). Moore's non-naturalism occupies a distinctive middle ground: "good" refers to a real property, but that property is not a natural one — it is known not through empirical observation but through a special faculty of moral intuition.

The book's reception was extraordinary. It became the bible of the Bloomsbury Group — the circle of writers, artists, and intellectuals that included Virginia Woolf, Lytton Strachey, John Maynard Keynes, and E.M. Forster — who were drawn to Moore's insistence that the good life consists in the enjoyment of beauty, friendship, and personal relationships. Keynes later wrote that Principia Ethica "was the most important book he had ever read" and that it had shaped the values of his generation more powerfully than any other philosophical work. Within academic philosophy, the book established the agenda for metaethics for the next half-century. The arguments Moore developed — the naturalistic fallacy, the open question argument, the concept of intrinsic value — became the starting points for virtually every serious work in ethical theory for decades.

Summary

The Naturalistic Fallacy

The naturalistic fallacy is the most famous concept in Principia Ethica, and it is also the most misunderstood. Moore did not use the term to refer to the error of deriving an "ought" from an "is" (that was a later usage, popularized by others). Moore's naturalistic fallacy is the error of identifying "good" with some natural property — of defining good as pleasure, or as desire-satisfaction, or as evolutionary fitness, or as anything else that can be described in naturalistic terms. The fallacy, Moore argued, is committed by virtually every moral philosopher who has tried to say what "good" means, from the utilitarians (who identify good with pleasure) to the evolutionary ethicists (who identify good with what is favored by natural selection) to the metaphysicians (who identify good with what God commands or with what conforms to the moral law).

Moore's argument that this is a fallacy rests on what he called the "open question" test. For any proposed naturalistic definition of "good" — say, "good means pleasurable" — we can always ask, intelligently and without contradiction, "But is pleasure good?" If "good" simply meant "pleasurable," then asking "is pleasure good?" would be like asking "is a triangle three-sided?" — the answer would be obvious and the question would be trivial. But "is pleasure good?" is not a trivial question. It is a genuine, open question, one that thoughtful people can and do disagree about. And the fact that it remains open, Moore argued, proves that "good" does not mean "pleasurable." The same test applies to every other naturalistic definition: "Is the maximization of desire-satisfaction good?" "Is evolutionary fitness good?" "Is obedience to God's commands good?" In every case, the question remains open, and in every case, the openness of the question shows that "good" has not been defined by the natural property in question.

The naturalistic fallacy is more than a logical point about definitions. It is, Moore believed, the deepest error in the history of ethics. By identifying good with some natural property, moral philosophers had systematically confused two different questions: "What is good?" (a question about the nature of goodness) and "What things are good?" (a question about which things possess the property of goodness). The first question, Moore argued, has no answer — good is indefinable. The second question is the real task of ethics, and it can only be answered by direct intuition of which things are good.

Good as Indefinable

Moore's positive thesis is that "good" is a simple, unanalyzable, non-natural property. The argument for this claim proceeds by analogy with colors. "Yellow" cannot be defined in terms of anything more basic — you cannot explain what yellow is to someone who has never experienced it. You can describe the physical properties of yellow light (wavelengths between 570 and 590 nanometers), but that description doesn't capture the quality of yellowness, the way yellow looks. Someone who knows the physics but has never seen yellow still doesn't know what yellow is. Yellowness is a simple quality, grasped directly through experience, and any attempt to define it in terms of something else will fail.

"Good," Moore argued, is analogous. It is a simple quality, grasped directly through moral intuition, and any attempt to define it in terms of something else commits the naturalistic fallacy. When we say "pleasure is good," we are not defining good as pleasure (that would make the statement a tautology). We are asserting a relationship between two distinct things — pleasure and goodness — and the assertion is a substantive moral claim that could be true or false. The same is true of any other statement of the form "X is good": it asserts that X possesses the non-natural property of goodness, and it is not reducible to any natural fact about X.

The non-natural character of goodness is crucial. Goodness, Moore insisted, is not a natural property — not a property that can be discovered by empirical investigation. You cannot observe goodness with the senses, the way you observe yellow or hot or heavy. You grasp it with a distinct cognitive faculty — moral intuition — which delivers immediate, self-evident judgments about what is good. This is the intuitionist element of Moore's position: moral truths are known not through experience or reasoning but through direct apprehension, in much the way that the axioms of geometry are known. The comparison with geometry was important to Moore, because it allowed him to claim that ethics is a genuine science — a body of objective truths about a real property — even though its subject matter is not natural.

Intrinsic Value

If "good" is indefinable, how do we determine what things are good? Moore distinguished between two senses of "good": instrumental good (good as a means to something else) and intrinsic good (good in itself, regardless of consequences). A medicine is instrumentally good because it produces health; health might be intrinsically good because it is good in itself. The central task of ethics, Moore argued, is to determine what things are intrinsically good — what things possess the property of goodness as an end, not merely as a means.

To identify intrinsically good things, Moore proposed what he called the "isolation test." To determine whether something is intrinsically good, you should ask: would the existence of this thing alone, in isolation from everything else, make the universe better than its non-existence? If the answer is yes, the thing is intrinsically good. The test is designed to strip away instrumental considerations — to isolate the intrinsic value of the thing from the value it derives from its consequences.

Moore applied this test and reached conclusions that were surprising for their time. The intrinsically good things, he argued, are not (as the utilitarians claimed) pleasures and the absence of pain. They are, above all, two things: the enjoyment of beauty (aesthetic appreciation) and the enjoyment of human affection (personal relationships and friendship). Pleasure is good, Moore conceded, but it is not the only good, and it is not the highest good. A universe filled with nothing but pleasure — a universe of passive, undifferentiated sensation — would be less valuable than a universe containing the appreciation of beauty and the warmth of personal love, even if the latter contained some pain. This was a direct challenge to the utilitarian orthodoxy that had dominated English moral philosophy since Jeremy Bentham and John Stuart Mill, and it reflected Moore's conviction that the moral life is richer and more complex than the utilitarians had allowed.

Moore also argued that certain combinations of things — what he called "organic unities" — have a value that is not simply the sum of the values of their parts. A beautiful painting is not just the sum of the values of its pigments and canvas; the whole has a value that emerges from the arrangement of the parts and that cannot be predicted from the values of the parts alone. This principle of organic unity allowed Moore to defend the intuition that certain complex states of affairs — a consciousness that appreciates beauty, a relationship of mutual affection — are more valuable than any analysis of their components would suggest.

Key Arguments

The Open Question Argument

The open question argument is the most influential single argument in Principia Ethica, and it remains, more than a century after its formulation, the starting point for most discussions of moral definition. The argument is deceptively simple. Take any proposed definition of "good" in terms of a natural property N. Now ask: "Is N good?" If the definition is correct — if "good" simply means N — then the question "Is N good?" should be trivial, answerable by inspection, like "Is a triangle three-sided?" But it isn't trivial. It is a genuine, substantive question that remains open even after the definition has been proposed. And the fact that it remains open, Moore concluded, proves that the definition is wrong. "Good" does not mean N, for any natural property N.

The power of the argument lies in its generality. It applies not just to utilitarian definitions ("good means pleasurable") but to every naturalistic definition: theological ("good means commanded by God"), evolutionary ("good means fitness-enhancing"), perfectionist ("good means fully developed"), sociological ("good means approved by society"). In every case, the question "Is N good?" remains open, and in every case, the openness of the question shows that the definition fails. The only definition that would not leave the question open is "good means good" — which is not a definition at all but a tautology. So "good" is indefinable.

The open question argument has been subjected to extensive criticism. The most influential objection, developed by philosophers in the mid-twentieth century, is that it conflates semantic and substantive questions. The fact that "Is pleasure good?" is an open question shows that "good" and "pleasurable" have different meanings — but it doesn't show that goodness and pleasure are different properties. Two terms can have different meanings but refer to the same property, just as "water" and "H2O" have different meanings but refer to the same substance. (This objection, which draws on Saul Kripke's and Hilary Putnam's work on reference, was not available to Moore, but it has become the standard response.) Other critics have argued that the open question argument proves too much: if it shows that "good" is indefinable, then by parity of reasoning it would show that every term is indefinable, since for any term T and any proposed definition D, one can always ask "Is D really T?" Moore's defenders have responded by arguing that these objections miss the point: the open question argument is not about meaning in the semantic sense but about the cognitive significance of moral claims, and the fact that "Is pleasure good?" is a substantive question shows that moral inquiry is not reducible to naturalistic inquiry.

The Argument Against Hedonism

Moore devoted a substantial portion of Principia Ethica to a critique of hedonism — the view, central to utilitarian ethics, that pleasure is the only intrinsic good and pain the only intrinsic evil. Moore's argument is not that pleasure is bad (he agreed that pleasure is good) but that it is not the only good and not the highest good. His strategy is to deploy the isolation test: imagine a universe containing nothing but pleasure and a universe containing the appreciation of beauty and the warmth of personal love. Which is better? Moore's intuition says the latter, and he argues that any honest moral intuition will agree. A world of mere pleasure — of passive, undifferentiated sensation, with no beauty, no knowledge, no love — is less valuable than a world containing these richer goods, even if the latter contains some pain.

This argument was revolutionary in its context. The utilitarian tradition, from Bentham through Mill, had treated pleasure as the sole intrinsic good and had built the entire structure of moral theory on that foundation. Moore's argument didn't merely challenge a particular version of utilitarianism; it challenged the fundamental axiom on which all versions of utilitarianism rested. If pleasure is not the sole intrinsic good, then the utilitarian calculus — which measures the rightness of actions by the amount of pleasure they produce — is measuring the wrong thing, and the entire utilitarian program needs to be rethought.

Moore's critique of hedonism also illustrates his method of moral intuition. He doesn't argue that beauty and love are more valuable than pleasure in the way that a mathematician argues for a theorem. He points to the relevant states of affairs and invites the reader to consult their own moral intuition. If the reader's intuition agrees (and Moore was confident that it would, at least in readers of good will and clear mind), then the conclusion follows. This method — of appealing to self-evident moral truths that are grasped directly rather than derived from more basic principles — is the essence of Moore's intuitionism, and it was both the strength and the vulnerability of his position. Its strength lay in its refusal to reduce moral truth to something else; its vulnerability lay in its dependence on the reliability of moral intuition, which later philosophers would subject to devastating criticism.

The Refutation of Subjectivism

Moore also argued against ethical subjectivism — the view that "good" means "what I desire" or "what is approved by society" or "what is commanded by God." His argument is a direct application of the open question test. If "good" meant "what I desire," then "Is what I desire good?" would be a trivial question, answerable by inspection. But it is not trivial — it is a genuine question that we can and do ask. The fact that we can meaningfully ask whether our desires are good shows that "good" does not mean "what I desire." The same argument applies to every subjectivist definition: we can always meaningfully ask whether what society approves or what God commands is good, and the meaningfulness of the question shows that goodness has not been identified with the object of approval or command.

This argument was important because it defended the objectivity of ethics against the relativistic and subjectivistic tendencies that were gaining ground in Moore's time (and that would become dominant in the twentieth century). If "good" refers to a real, non-natural property, then moral judgments are objectively true or false — they describe the world as it is, not merely as we feel about it. This objectivism was central to Moore's philosophical identity and to the identity of the analytic tradition in ethics that he founded. It would be challenged by the non-cognitivists (Ayer, Stevenson, Hare) who argued that moral judgments are not descriptions at all but expressions of attitude, and by the error theorists (Mackie) who argued that moral judgments purport to describe but always fail because there are no moral properties. But these challenges were formulated in response to Moore, and the debate between Moorean objectivists and their critics has structured metaethics ever since.

Legacy

Principia Ethica transformed moral philosophy. Its influence has been so pervasive that it is difficult to identify a major work in twentieth-century ethics that does not, in some sense, define itself in relation to Moore's arguments.

In metaethics, the naturalistic fallacy and the open question argument set the agenda for the entire field. The question of whether "good" can be defined in naturalistic terms — and what this means for the objectivity of ethics — became the central question of metaethics, and remains so today. The non-naturalism Moore defended spawned a tradition of intuitionist ethics (Prichard, Ross, Ewing) that held sway in British philosophy for decades. The naturalists regrouped, developing more sophisticated forms of naturalism (Cornell realism, naturalized ethics) that attempted to evade the open question argument. The non-cognitivists, who agreed with Moore that "good" couldn't be defined naturally but concluded that "good" doesn't refer to a property at all, created a third tradition that dominated mid-century ethics. All of these positions were defined in relation to Moore, and the metaethical landscape he created is still the one in which contemporary debates take place.

In normative ethics, Moore's critique of hedonism opened the door to a richer, pluralistic conception of value. The idea that pleasure is the sole intrinsic good was never again accepted without serious qualification. Moore's insistence that beauty, knowledge, and love are intrinsically good, and that their goodness is not reducible to the pleasure they produce, helped create the intellectual space for value pluralism. This pluralism has influenced contemporary theories of well-being and enriched the debate about what makes a life go well.

Beyond philosophy, Principia Ethica had remarkable cultural influence. The Bloomsbury Group — the circle of writers and intellectuals including Virginia Woolf, Lytton Strachey, John Maynard Keynes, and E.M. Forster — adopted Moore's ethics as their credo. They were drawn to his insistence that the highest goods are the enjoyment of beauty and the warmth of personal relationships, and they built their lives and art around these values. Keynes later wrote that Principia Ethica had done more to shape the values of his generation than any other book.

The enduring significance of Principia Ethica lies in the combination of philosophical ambition with extraordinary analytical precision. Moore set out to answer the most fundamental question in ethics — what is good? — with an argument so clear and powerful that it has shaped every subsequent attempt to answer it. Whether one agrees with Moore's non-naturalism or not, one cannot do ethics without engaging with his arguments. The naturalistic fallacy, the open question argument, the distinction between intrinsic and instrumental value, the principle of organic unities — these are living tools that philosophers continue to use. More than a century after its publication, Principia Ethica remains a work that no serious student of ethics or analytic philosophy can afford to ignore — a text that reshaped the questions philosophers ask about knowledge, truth, and the understanding of reality.