On Alasdair MacIntyre's After Virtue: A Study in Moral Theory (1981), mostly ch. 3-7 and 14-17. What justifies ethical claims? MacIntyre claims that no modern attempt to ground ethics has worked, and that's because we've abandoned Aristotle. We see facts and values as fundamentally different: the things science discovers vs. these weird things that have nothing to do with science. In Aristotle's teleological view, everything comes with built-in goals, so just as a plant will aim grow green and healthy, people have a definite kind of virtue towards which we do and should naturally strive. Get the full discussion at partiallyexaminedlife.com.