Principia Ethica : G . E. Moore

Another book I am mentioning here is G. E. Moore's Principa Ethica. Moore is one of the most important, and the most overlooked, figures in Analytic philosophy. All too many historical surveys of early Analytic philosophy treat him as attached to Bertrand Russell’s hip, and as soon as they have got done discussing their joint break with Absolute Idealism and offered a rather Russellian understanding of Moore’s work on Analytic method, they pretty quickly move on to talk about what’s taken to be the heavy-duty stuff: Principia Mathematica, Wittgenstein, and the Vienna Circle. All of this is too damn bad; for as valuable as the parts of Analytic method that Moore and Russell developed more or less in tandem are, there are in the end deep differences between Moore and Russell, in the motivations that led each to adopt Analytic method and the understanding of the aim and right method of philosophy that resulted for each.

G. E. Moore in his seminal Principia Ethica stated that a naturalistic fallacy was committed whenever a philosopher attempts to prove a claim about ethics by appealing to a definition of the term "good" in terms of one or more natural properties (such as "pleasant", "more evolved", "desired", etc.).

The naturalistic fallacy is related to, and often confused with, the is-ought problem (as formulated by, for example, David Hume). As a result, the term is sometimes used loosely to describe arguments that claim to draw ethical conclusions from natural facts.
Alternately, the phrase "naturalistic fallacy" is used to refer to the claim that what is natural is inherently good or right, and that what is unnatural is bad or wrong.

This book, I love a lot.