Abstract. “Legalism” is defined as requiring that all matters of legal regulation and controversy ought so far as possible to be conducted in accordance with predetermined rules of considerable generality and clarity. Thus there may be moral limits on governments which ban them from acting on the substantive moral merits of situations with which they have to deal. This is most important in public law, but also applies in private law, e.g., in cases involving property. Hume, Kant, and Hayek are examined in respect of their case for legalism; Alexy and Finnis also reviewed. Autonomy is the foundation for legalism, and justifies “ethical positivism,” in T. Campbell's phrase. Critical legal studies (Unger, Kelman, Kennedy et al.) however challenge legalism's premises. But the “critical” arguments against reification merely raise, they do not settle, the issue about the politics of legalism and the desirability of legal dogmatics. With all faults, legalism is a prerequisite of free government.