Formal Legality for Nudges

Abstract Nudges are small psychological prompts that steer behavior in a noncoercive way. For example, low‐calorie products can be placed at eye level to encourage people to eat healthier. This article argues that governmental nudges are in tension with Fuller's formal legality principle, according to which regulation should meet requirements such as generality and promulgation. Moreover, it shows that this tension can be solved by taking two steps. The first consists in revising the principle of legality in light of the psychological insights that have inspired the theory of nudging; the second in tweaking the requirements of legality so as to arrive at a special legality principle for nudges.