The naturalistic fallacy is often claimed to be a formal fallacy. It was described and named by British philosopher G. E. Moore in his 1903 book Principia Ethica. Moore stated that a naturalistic fallacy is 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", "more evolved", "desired", etc.). Arthur N. Prior defined it as
…the assumption that because some quality or combination of qualities invariably and necessarily accompanies the quality of goodness, or is invariably and necessarily accompanied by it, or both, this quality or combination of qualities is identical with goodness. If, for example, it is believed that whatever is pleasant is and must be good, or that whatever is good is and must be pleasant, or both, it is committing the naturalistic fallacy to infer from this that goodness and pleasantness are one and the same quality. The naturalistic fallacy is the assumption that because the words 'good' and, say, 'pleasant' necessarily describe the same objects, they must attribute the same quality to them. 
The naturalistic fallacy is related to (and even confused with) the is-ought problem, which comes from Hume's Treatise. The term is sometimes used loosely to describe arguments that claim to draw ethical conclusions from natural facts. This view is in opposition to some forms of ethical naturalism.
Alternatively, the phrase "naturalistic fallacy" is used to refer to the claim that what is natural is inherently good or right, and that what is unnatural is bad or wrong (see "Appeal to nature"). It is the converse of the moralistic fallacy, the notion that what is good or right is natural and inherent.
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). 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. Yellow, then, may be understood as a quale; 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, 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.
Moore advanced an argument for the indefinability of “good” (and demonstrating the “naturalistic fallacy”) which is known as the Open Question Argument.
Appeal to nature
Some people use the phrase "naturalistic fallacy" or "appeal to nature" to characterize 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. While such inferences may indeed be fallacious, Moore is not concerned with them. He is instead concerned with the semantic and metaphysical underpinnings of ethics. However, emotivists like Charles Leslie Stevenson hold that it may be reasonable to assert that the term "good" is merely an affirmation of approval and that, as such, good may be defined as "I approve."
Philosophers such as St. Thomas Aquinas held that the "good" was a process of actualization where the formal principle of a natural object fulfilled its final cause (purpose) such that a tree's purpose is to develop another tree or a bouncy ball's is to bounce. The formal principle to Aquinas was defined through Aristotle as "that which makes a thing what it is." Thus the source of potency to accomplish all natural object ends is through the formal cause of an object. For which Aquinas suggests a non-dualistic model for substance: Form and Matter. Aquinas held that what is good is what is natural in that God created all things and they were good. However, he argued from human reason rather than faith when he discussed the ontological significance. He suggested that the end (fulfillment of its purpose) is the good and there are various degrees of Good, such as the processes of development in a living being. Arguably, happiness is the ultimate end for all human beings and thus all morality is in reference to what actualizes this "happiness." But Aquinas argued that there was an objective principle, not relative, which accomplished self-actualization. A simple example is that drugs simulate happiness but are only "apparent/false" happiness while integrity, reason, and love all flow with nature and therefore permit actualization of the ultimate end: happiness.
The is-ought problem
The term "naturalistic fallacy" is also sometimes used to describe the deduction of an "ought" from an "is" (the Is-ought problem), and 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." An example of a naturalistic fallacy in this sense would be to conclude Social Darwinism from the theory of evolution by natural selection, and of the reverse naturalistic fallacy to argue that the immorality of survival of the fittest implies the theory of evolution is false. Moralists Jeremy Bentham and Immanuel Kant both indicated the is-ought problem in order to identify their theories of morality and law.
In using his categorical imperative Kant deduced that experience was necessary for their applications. But experience on its own or the imperative on its own could not possibly identify an act as being moral or immoral. We can have no certain knowledge of morality from them, being incapable of deducing how things ought to be from the fact that they happen to be arranged in a particular manner in experience.
Bentham, in discussing the relations of law and morality, found that when people discuss problems and issues they talk about how they wish it would be as opposed to how it actually is. This can be seen in discussions of natural law and positive law. Bentham criticized natural law theory because in his view it was a naturalistic fallacy, claiming that it described how things ought to be instead of how things are.
According to Bernard Williams, Moore's use of the phrase 'naturalistic fallacy' to describe this particular kind of meta-ethical thinking was a 'spectacular misnomer'; Williams contending that it is not properly either naturalistic or a fallacy. Far from clear is whether the thinkers Moore criticised, even supposing he were right in those criticisms, were committing an error of inference - the true meaning of 'fallacy' - rather than simply a metaphysical mistake, or a dubious redefiniton. Moreover, the mistake being made is not very closely related to what would ordinarily be considered either moral or metaphysical naturalism. Moore's arguments may rule out attempts to define 'goodness' in such obviously naturalistic terms as 'happiness', but no less do they preclude similar attempts to define the good in terms of God's will — in other words, divine command theory, not an ethic which could sensibly be described as naturalistic at all.
Science and moral questions
Some scientists and philosophers reject the Naturalistic Fallacy, arguing that it is indeed possible to derive "ought" from "is", and even that it has already been done to some extent. Proponents of this view see morality as a budding science. This view is critical of Moore's "simple indefinable terms" (which amount to qualia), arguing instead that such terms actually can be broken down into constituents.
- Appeal to novelty
- Appeal to tradition
- Definist fallacy
- Evolution of morality
- Fact-value distinction
- Moralistic fallacy
- Philosophical naturalism
- Norm (philosophy)
- Value theory
- Moore, George Edward (1903). Principia Ethica. Cambridge: Cambridge University Press. http://fair-use.org/g-e-moore/principia-ethica.
- 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
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