The ethical and legal thought of Thomas Aquinas and F. A. Hayek emerged out of distinct philosophical traditions. Aquinas, following the Aristotelian tradition, emphasized the inexact character of ethics and hence the mutability of law due to the contingency of particular circumstances. Hayek, relying on Kant, advocated a view of law as universal and general rules of conduct not intended to achieve particular, substantive social goals. Despite these differences in philosophical orientation, the legal theories of Aquinas and Hayek converge in their mutual recognition of the limits of law and legislation. Both believed that the legislator’s ability to address and solve social problems through the statutory enactment of rules is severely limited. In light of these limits, both Aquinas and Hayek appealed to custom as an effective source of law and thus as an alternative to legislation.