Metaethics is the study of moral language, moral ontology, and moral epistemology. This book addresses each of these in a way accessible to both students and professional philosophers. Van Reken defends the classic view of moral realism, advanced by philosophers such as Plato, Aristotle, Augustine, and Kant. Moral language tends to be the focus of much current metaethical discussion, but this volume concerns itself more with questions of moral ontology and moral epistemology. The concept of the moral field is introduced, which helps distinguish what is moral and what is amoral (a discussion too often overlooked by moralists), and--adapting an epistemological theory developed by Alvin Plantinga--an argument is made that we can know moral truths. Principia Meta-Ethica presents a return to the core issues of metaethics and strengthens the case for moral realism with new arguments, distinctions, and concepts.