Often, in a case of first instance, a judge will reach a decision by an appeal to legal principles. For example, in the 1889 case of Riggs v. Palmer a New York court had to decide whether a grandson who had murdered his grandfather could inherit under the will in which his grandfather had named him an heir. The statutes and rules of testamentary law did not prohibit the inheritance. The court, however, invoked the legal principle that no one should be permitted to profit by his own wrong and denied the claim to inheritance. The use of such principles by courts raises an important question for legal theory: Do these principles exist within or without the legal system? This note argues that an adequate conception of a legal system must inclu...