G.E. Moore is often remembered for his exposition of the the 'naturalistic fallacy,' which he explained in "Principia Ethica" by thrashing the views of Herbert Spencer, in particular. In this book, Moore addresses questions such as "What is 'good'?" and "How can one know?" Utilitarianism offered one answer, which Moore did not find fully satisfactory. Moore's arguments illustrate that something one may have thought was completely self-evident, that is, the nature of 'good,' is not as clear cut as one may believe.