Full Idea
The naturalistic fallacy ..consists in the contention that good means nothing but some simple or complex notion, that can be defined in terms of natural qualities.
Gist of Idea
The naturalistic fallacy claims that natural qualties can define 'good'
Source
G.E. Moore (Principia Ethica [1903], §044)
Book Reference
Moore,G.E.: 'Principia Ethica' [CUP 1980], p.73
A Reaction
Presumably aimed at those who think morality is pleasure and pain. We could hardly attribute morality to non-human qualities. I connect morality to human deliberative functions.