1. The Open Question Argument and its Aftermath: Moore’s Influence on Russell Russell’s destiny as an ethical thinker was dominated by one book—G.E. Moore’s Principia Ethica (1903). Before 1903, Russell devoted some of the energy that he could spare from German Social Democracy, the foundations of mathematics and the philosophy of Leibniz to working out a meta-ethic of his own. After 1903, he became an enthusiastic but critical convert to the doctrines of Principia Ethica (though there is some evidence that the conversion process may have begun as early as 1897). Moore is famous for the claim, which he professes to prove by means of what has come to be known as the Open Question Argument, that there is a “non-natural” property of goodness , not identical with or reducible to any other property or assemblage of properties, and that what we ought to do is to maximize the good and minimize the bad. Russell subscribed to this thesis—with certain important reservations—until 1913.…