Naturalistic fallacy

In philosophical ethics, the term "naturalistic fallacy" was introduced by British philosopher G. E. Moore in his 1903 book Principia Ethica. Moore argues it would be fallacious to explain that which is good reductively in terms of natural properties such as "pleasant" or "desirable".

Moore's naturalistic fallacy is closely related to the is–ought problem, which comes from David Hume's A Treatise of Human Nature (1738–40). However, unlike Hume's view of the is–ought problem, Moore (and other proponents of ethical non-naturalism) did not consider the naturalistic fallacy to be at odds with moral realism.

The term "naturalistic fallacy" is sometimes used to describe the deduction of an "ought" from an "is" (the is–ought problem).

In using his categorical imperative Kant deduced that experience was necessary for their application. 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 G. E. Moore's Principia Ethica, when philosophers try to define "good" reductively in terms of natural properties like "pleasant" or "desirable", they are committing the naturalistic fallacy.

...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.

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