In philosophical ethics, the naturalistic fallacy is the claim that it is possible to give a reductive explanation of good, in terms of natural properties such as pleasant or desirable. The term was introduced by British philosopher G. E. Moore in his 1903 book Principia Ethica.
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 naturalistic fallacy should not be confused with the appeal to nature, which is exemplified by forms of reasoning such as "Something is natural; therefore, it is morally acceptable" or "This property is unnatural; therefore, this property is undesirable." Such inferences are common in discussions of medicine, sexuality, environmentalism, gender roles, race, and carnism.
Is–ought problem
The term naturalistic fallacy is sometimes used to describe the deduction of an ought from an is (the is–ought problem). This usually takes the form of saying that If people do something (e.g., eat three times a day, smoke cigarettes, dress warmly in cold weather), then people ought to do that thing. It becomes a naturalistic fallacy when the is–ought problem ("People eat three times a day, so it is morally good for people to eat three times a day") is justified by claiming that whatever practice exists is a natural one ("because eating three times a day is pleasant and desirable").
In using his categorical imperative, Kant deduced that experience was necessary for its 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.