Environmental regulators must sometimes decide whether to install rules absent full information about either a risk’s or a precaution’s costs. In Europe, recourse is had to a “precautionary principle” that warrants intervention not­withstanding epistemic gaps. While debate persists about how to formulate the precautionary principle, American scholars have leveled withering criticism of its strong form’s incoherence. “Take every precaution,” they argue, is infeasible, even paralyzing, counsel.

Constitutions, Adrian Vermeule notes, are tools for managing risks. Ver­meule detects precautionary reasoning across American constitutional thought. He finds it in Chief Justice John Marshall’s sweeping repudiation in McCulloch v. Maryland of states’ authority to tax federal institutions such as the Bank of the United States. More recently, Vermeule argues, precautionary logic has underwritten narrow construction of the President’s recess appoint­ment power. In both cases, government power is constrained based on fear of future abuse. Generalizing, Vermeule suggests that precautionary logic is typically employed to underwrite “narrow construction” (p. 53) of governme