Principia Ethica

Principia Ethica is a book by the British philosopher G. E. Moore, originally printed in 1903, in which Moore argues the indefinability of "good" and gives an exposition of the naturalistic fallacy. Principia Ethica was widely influential, and Moore's arguments were long regarded as path-breaking advances in moral philosophy, though they have been seen as less impressive and durable than his contributions in other fields.