The use of such general descriptive words or labels as ‘Naturalism’, ‘Realism’ and ‘Idealism’ can hardly be avoided in writing the history of philosophy, but it can sometimes be misleading. Philosophy is written by individuals, not by schools or groups. Labels, where they are correctly and sensibly applied, are signs of resemblances and affinities between the various things to which any one label is affixed; but those resemblances and affinities are not the whole story, and not all naturalists or realists or idealists give identical answers to identical questions. It is especially important to guard against the danger of wrongly reading back into history the disputes and arguments of one’s own day; however understandable may be the desire to strengthen one’s own case by finding it anticipated in the work of one’s most distinguished predecessors, the history of philosophy repeats itself no more exactly than the history of any other human activity. The philosophical views and arguments discussed in this essay were not designed, and should not on the whole be interpreted, as contributions to the twentieth-century debate on ethical naturalism which was initiated by G. E. Moore’s supposed discovery of the Naturalistic Fallacy (in Principia Ethica, first published in 1903).