The standard view of judicial motivation is pluralist. Many considerations, on this view, motivate judges to apply the law. Perhaps they do so out of fear, or greed, or—on some occasions—because it is the right thing to do. Here I defend a competing view. Judges must believe legal duties are moral duties. That belief explains their enforcement of those duties. Various features of legal practice support this inference. Judges often render decisions the merits of which they vehemently disagree. They take pride in the lawfulness of such decisions, and are angry at the lawlessness of others. Those features of legal practice are only intelligible if a decisive number of judges were to believe legal duties are moral duties. Judges must believe possess this belief for certain core features of legal practice to obtain.