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George Edward Moore

The naturalistic fallacy is an alleged logical fallacy, identified by British philosopher G.E. Moore in Principia Ethica (1903), which Moore stated was committed whenever a philosopher attempts to prove a claim about ethics by appealing to a definition of the term "good" in terms of one or more natural properties (such as "pleasant", "healthy", "natural", etc.).

The naturalistic fallacy is related to, and often confused with, the is-ought problem (as formulated by, for example, David Hume). As a result, the term is sometimes used loosely to describe arguments which claim to draw ethical conclusions from natural facts. Even more distantly, the term is used to describe arguments which claim to draw ethical conclusions from the fact that something is "natural" or "unnatural."

Moore's discussion

Moore's argument in Principia Ethica is (among other things) a defense of ethical non-naturalism; he argues that the term "good" (in the sense of intrinsic value) is indefinable, because it names a simple, non-natural property. It is, rather, "one of those innumerable objects of thought which are themselves incapable of definition, because they are the ultimate terms by reference to which whatever is capable of definition must be defined" (Principia Ethica § 10 ¶ 1). By contrast, many ethical philosophers have tried to prove some of their claims about ethics by appealing to an analysis of the meaning of the term "good"; they held, that is, that "good" can be defined in terms of one or more natural properties which we already understand (such as "pleasure", in the case of hedonists, or "survival", in the case of evolutionary ethics). Moore coined the term "naturalistic fallacy" to describe arguments of this form; he explains (in § 12) that the fallacy involved is an instance of a more general type of fallacy, which he leaves unnamed, but which we might call the "definitional fallacy". The fallacy is committed whenever a statement to the effect that some object has a simple indefinable property is misunderstood as a definition that gives the meaning of the simple indefinable property:

That "pleased" does not mean "having the sensation of red", or anything else whatever, does not prevent us from understanding what it does mean. It is enough for us to know that "pleased" does mean "having the sensation of pleasure", and though pleasure is absolutely indefinable, though pleasure is pleasure and nothing else whatever, yet we feel no difficulty in saying that we are pleased. The reason is, of course, that when I say "I am pleased", I do not mean that "I" am the same thing as "having pleasure". And similarly no difficulty need be found in my saying that "pleasure is good" and yet not meaning that "pleasure" is the same thing as "good", that pleasure means good, and that good means pleasure. If I were to imagine that when I said "I am pleased", I meant that I was exactly the same thing as "pleased", I should not indeed call that a naturalistic fallacy, although it would be the same fallacy as I have called naturalistic with reference to Ethics.

— G. E. Moore, PE § 12

The point here is connected with Moore's understanding of properties and the terms that stand for them. Moore holds (§7) that properties are either complexes of simple properties, or else irreducibly simple. The meaning of terms that stand for complex properties can be given by using terms for their constituent properties in a definition; simple properties cannot be defined, because they are made up only of themselves and there are no simpler constituents to refer to. Besides "good" and "pleasure", Moore also offers colour terms as an example of indefinable terms; thus if one wants to understand the meaning of "yellow", one has to be shown examples of it; it will do no good to read the dictionary and learn that "yellow" names the colour of egg yolks and ripe lemons, or that "yellow" names the primary colour between green and orange on the spectrum, or that the perception of yellow is stimulated by electromagnetic radiation with a wavelength of between 570 and 590 nanometers. It is true that yellow is all these things, that "egg yolks are yellow" and "the colour perceived when the retina is stimulated by electromagnetic radiation with a wavelength of between 570 and 590 nanometers is yellow" are true statements. But the statements do not give the meaning of the term "yellow", and (Moore argues) to confuse them with a definition of "yellow" would be to commit the same fallacy that is committed when "Pleasure is good" is confused with a definition of "good".

Moore goes on to explain that he pays special attention to the fallacy as it occurs in ethics, and identifies that specific form of the fallacy as ‘naturalistic’, because (1) it is so commonly committed in ethics, and (2) because committing the fallacy in ethics involves confusing a natural object (such as survival or pleasure) with goodness, something that is (he argues) not a natural object. However, it's important to note that in spite of his rhetorical focus on the ‘naturalistic’ nature of the fallacy, Moore was not any more satisfied with theories that attempted to define goodness in terms of non-natural properties than he was with naturalistic theories; indeed, the basis of his criticism of “Metaphysical Ethics” in Chapter IV of Principia Ethica is that theories which define 'good' in terms of supernatural or metaphysical properties rest on the very same fallacy as naturalistic theories (§69). The target of Moore's discussion of the "naturalistic fallacy" is reductionism at least as much as it is naturalism specifically, and the important lesson, for Moore, is that the meaning of the term "good" and the nature of the property goodness are irreducibly sui generis.

The Open Question Argument

Moore's argument for the indefinability of “good” (and thus for the fallaciousness of the “naturalistic fallacy”) is often called the Open Question Argument; it is presented in §13 of Principia Ethica. The argument hinges on the nature of statements such as "Anything that is pleasant is also good" and the possibility of asking questions such as "Is it good that x is pleasant?" According to Moore, these questions are open and these statements are significant; and they will remain so no matter what is substituted for "pleasure". Moore concludes from this that any analysis of value is bound to fail. In other words, if value could be analyzed, then such questions and statements would be trivial and obvious. Since they are anything but trivial and obvious, value must be indefinable. Critics of Moore's arguments sometimes claim that he is appealing to general puzzles concerning analysis (cf. the paradox of analysis), rather than revealing anything special about value. Other responses appeal to the Fregean distinction between sense and reference, allowing that value concepts are special and sui generis, but insisting that value properties are nothing but natural properties (this strategy is similar to that taken by non-reductive materialists in philosophy of mind).

Related uses

Many people use the phrase "naturalistic fallacy" to characterise inferences of the form "This behaviour is natural; therefore, this behaviour is morally acceptable" or "This behaviour is unnatural; therefore, this behaviour is morally unacceptable". Such inferences are common in discussions of homosexuality and cloning, to take two examples. (See this article on homosexuality by Massimo Pigliucci, and Social Darwinism.) While such inferences may indeed be fallacious, it is important to realise that Moore is not concerned with them. He is instead concerned with the semantic and metaphysical underpinnings of ethics.

Additionally, many alternative health advocates fall in to the naturalistic fallacy because they claim that because something is natural, it is safe and effective as a health treatment. Unfortunately, this is wrong both on principle (nature has made poison ivy, snake venom and the bubonic plague which are neither safe nor effective as medicine) and in practice (St. John's Wort is a natural herb sometimes used by herbalists as a treatment for depression and can be very dangerous when misused). Similarly with genetic modification, many opponents claim that it is unnatural and, by definition, undefendable. Similarly, organic foods are often defended on the basis that they are "natural", and therefore have qualities which non-organic products do not have, even if the two are indistinguishable.

This use of the term "naturalistic fallacy" to describe the deduction of an "ought" from an "is" (the Is-ought problem), has inspired the use of mutually reinforcing terminology which describes the converse (deducing an "is" from an "ought") either as the "reverse naturalistic fallacy" or the "moralistic fallacy".

A common use of the reverse naturalistic fallacy is the argument that the immorality of survival of the fittest (if it were practised by people) has a bearing on whether the theory of evolution is true:

In its simplest form, evolution represents the view that the ordering principle of reality is "the survival of the fittest", or that outcomes validate themselves simply by occurring. So if there is any standard at all, that standard is simply "what works". Whether you want to call it survival, dominance or superiority, the standard is simply "what works".
Whatever works for you! That summarises the standard that is implied by evolutionary theory...
If we are a people whose understanding of justice derives from the belief that all of us are created equal, and that the will of the Creator therefore has authority in determining human justice, then the question of creation vs. evolution is not just a question of scientific theory, it is a question of the utmost political significance. Evaluating the scientific discussion about evolution is sometimes difficult for the non-specialist. But the importance to our political and moral lives of facing the question should be immediately evident to anyone who remembers what it means to be an American, and who hopes to see justice prevail over the rule of tooth and claw. (Alan Keyes, 2001 [1])


Moore, George Edward (1903). Principia Ethica. Cambridge: Cambridge University Press.

See also

Further reading

  • Curry, O. (2006). Who's afraid of the naturalistic fallacy? Evolutionary Psychology, 4, 234-247. Full text
  • Walter, A. (2006). The anti-naturalistic fallacy: Evolutionary moral psychology and the insistence of brute facts. Evolutionary Psychology, 4, 33-48. Full text
  • Wilson, D. S., Dietrich, E., et al. (2003). On the inappropriate use of the naturalistic fallacy in evolutionary psychology. Biology and Philosophy, 18, 669-682. Full text

External links

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