Naturalistic Fallacy

"What's Crack?"
G.E. Moore believed that Naturalism had committed a fallacy in attempting to define something that was indefinable, i.e. terms such as good (which Moore felt were non-natural) and that naturalists tried to define it in naturalistic terms, like Pleasant, or Desirable (though, to be fair, that was kind of their schtick). In particular, Moore singled out utilitarianism as being especially guilty.

This argument can also be seen as the ought, section of the Is/Ought gap, I.e, he was telling off Mill and the crew for suggesting that something natural could give you an imperative. For example, in the utilitarian case of 'good': freeing a captive Mary from her room would make her happy, therefore you ought to do it. The first statement is factual, but it doesn't lead on that it just because it would increase happiness, you should do it.

The super imaginative name comes from a derivative of the two things he was talking about, namely, the fallacy of the naturalists. He certainly did some work on it, but he really could have put Moore effort into the title.