Taking metaphysics seriously: Kant on the foundations of ethics

Abstract Ask most philosophers for an example of a moral rationalist, and they will probably answer “Kant.” And no wonder. Kant's first great work philosophy, Groundwork the Metaphysics Morals , opens with clarion call rationalism, proclaiming need to out once pure metaphysics morals. That this includes principle ethics, law, is obvious. But what about second principles, particular laws, such as duties truthfulness, beneficence, etc.? Are these principles metaphysical too? Many have thought not, since make essential use empirical anthropological considerations. I argue otherwise; are fact matters. do by taking seriously morals—more specifically, understanding morals alongside nature. For, qua metaphysics, both employ common two‐stage methodology, stage which wholly priori but partly empirical. As explain, appreciating methodology sheds new light on how be established, well reach rationalism.