This chapter sketches four forms of realism ascribed to four great historical figures that provide an important set of determinate versions of moral realism. Plato provides a picture according to which moral facts exist in a non-concrete realm of abstract universal properties. Aristotle provides a picture according to which moral facts exist as concrete facts in the world. Hume provides a picture according to which moral facts have their basis in universal human sentiments. Kant provides a picture according to which (...) moral facts are simply truths of universal reason. It is argued that the revolution in our understanding of metaphysical explanations that occurred between Aristotle and Hume has important consequences for realist views. (shrink)