My first task is to define the subject. When I use the term law, I am distinguishing the category from other kinds of law such as positive law, divine law, or scientific law. When we discuss positive law, we look to materials like legislation, judicial opinions, and scholarly analysis of these materials. If we speak of divine law, we ask if there are any knowable commands from God. If we look for scientific law, we conduct experiments, or make observations and calculations, in order to come to objectively verifiable knowledge about the material world. Natural law-as I will be using the term in this essay-refers to a method that we employ to judge what the principles of individual morality or positive law ought to be. The natural law philosopher aspires to make these judgments on the basis of reason and human nature without invoking divine revelation or prophetic inspiration. Natural law so defined is a category much broader than any particular theory of natural law. One can believe in the existence of natural law without agreeing with the particular systems of natural law advocates like Aristotle or Aquinas. I am describing a way of thinking, not a particular theory. In the broad sense in which I am using the term, therefore, anyone who attempts to found concepts of justice upon reason and human nature engages in natural law philosophy. Contemporary philosophical systems based on feminism, wealth maximization, neutral conversation, liberal equality, or libertarianism are natural law philosophies. They start with assumptions about human nature and what is good for people, and they claim to employ reason to judge the relative justice or injustice of legal practices like slavery, the free market, patriarchy, and socialism. Like the man who was astonished to find that he had been speaking in prose all his life, we who make it our business to resolve differences about questions of morality and justice through the use of reason are surprised to find that we are expounding natural law. Next I should explain what I mean by reason, an ability available in theory to all humanity, however warped it may be in particular individuals or groups. Reason consists of two components: logic and clearheaded perception of reality. The rational mind must possess both qualities. For example, some paranoids have an impressive ability to think