Abstract
Exploring the joint dynamics of laws and social norms helps understand when social norms are sticky or adaptive. Using the example of the social and physical distancing measures introduced to contain the COVID-19 pandemic in 2020, we studied whether introducing, and then lifting, distancing regulations led individuals to quickly change their habits, not only by modifying the monetary incentives of rule violators but also by shifting the individuals' perception of the appropriateness of social encounters. We conducted an online incentivized experiment in France, where we elicited the same participants' perceived norm and social distancing behavior every week for three months. We find that both norm perception and behavior shifted as soon as the government introduced or removed social distancing measures. This effect was fast acting and long lasting, a result that highlights the importance of the expressive power of the law for norm formation and behavior.