this was an error. Unlike Prichard, Moore thought that one could derive principles of obligation from propositions about what is good. W. D. Ross's intuitionism was influenced both by Prichard and Moore. He holds that we can know moral truths through intuition, for example, that it is wrong to lie or that knowledge is intrinsically good. Intuitions involve a direct apprehension that is not mediated by inferences or deductions: they are self-evident and therefore not in need of any additional proof. This ability is not inborn but has to be developed on the way to reaching mental maturity. But in its fully developed form, we can know moral truths just as well as we can know mathematical truths like the axioms of geometry or arithmetic. This self-evident knowledge is limited to general principles: we can come to know the prima facie duties this way, e.g. that, generally speaking, one should keep one's promises and refrain from harming others. But intuition is unable to reveal one's absolute duty in a particular situation: what one should do all things considered. All we can do is consult perception to determine which prima facie duty has the highest normative weight in this particular case, even though this usually does not amount to knowledge proper due to the complexity involved in most specific cases. Ethical intuitionism suffered a dramatic fall from favor by the middle of the century, due in part to the influence of logical positivism, in part to the rising popularity of naturalism in philosophy, and in part to philosophical objections based on the phenomenon of widespread moral disagreement. C. L. Stevenson's emotivism would prove especially attractive to Moorean intuitionists seeking to avoid ethical naturalism. In the later parts of the 20th century, intuitionism would have few adherents to speak of; in Bernard Williams' words: "This model of intuition in ethics has been demolished by a succession of critics, and the ruins of it that remain above ground are not impressive enough to invite much history of what happened to it." Contemporary developments Some recent work suggests the view may be enjoying a resurgence of interest in academic philosophy. Robert Audi is one of the main contemporary supporters of ethical intuitionism. His 2005 book The Good in the Right claims to update and strengthen Rossian intuitionism and to develop the epistemology of ethics. Michael Huemer's book Ethical Intuitionism (2005) also provides a recent