In Western philosophy, the study of human psychology and of ethics has been intertwined since before the time of Plato. Plato relies on Greek psychology’s account of the three parts of the soul—the rational, the appetitive and the spirited, and describes the just person and just state as ones who align those parts into a harmonious whole. A balanced person, for Plato, is what we would call an ethical person. But if Plato were alive today, he would be accused of muddling the normative and the descriptive, or of deriving what ought to be from what is, an objection first made famous by David Hume in the 17th century and reiterated by G. E. Moore in the early twentieth century.