Tamar Gendler, teaching Yale's Philosophy and the Science of Human Nature, lays out Plato's analogy between the city-state and the soul and his answer to Glaucon's challenge that justice is intrinsically valuable because it is the well-ordered functioning of the soul's parts. She connects this ancient argument to modern psychology, bringing in Jonathan Haidt's account of the hedonic treadmill and the progress principle to test whether Plato's picture of harmony maps onto contemporary findings about happiness. The lecture closes with an introduction to Aristotle's claim that reflection and reasoning constitute the distinctive function of human beings and therefore the highest good. Gendler opens with a classroom poll on a voluntary no-Internet pledge before turning to the substantive material. Recorded in Spring 2011 as part of the Open Yale Courses series, the talk moves briskly from ancient text to empirical research and back, treating the two as genuinely in conversation rather than separate exercises.