What is "naturalistic fallacy"

n. Any attempt to verbally define "good", instead of treating it as an undefined term, in terms of which other terms are defined.

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.