A central tenet of positivism is that social practices are at the foundations of law. This has been cashed out in a variety of ways. For example, Austin argues that, among other practices, a habit of obedience to a sovereign is at the foundations of law, and Hart argues that at the foundations of law is the converging attitudes and behaviors of a class of relevant officials. Since Hart, some prominent positivists have employed either David Lewis's analysis of conventions or Michael Bratman's theory of shared cooperative activities to develop new accounts of the social practices that are at the foundations of law, whatever those foundations might be. In this paper, I identify five features characteristic of the Lewisean and Bratmanian models of social facts—models of what I call hypercommittal social practices. I then show that models of social facts that have these features ought not to be used to explain the way in which a social practice is at the foundations the law. I conclude that hypercommittal social practices such as Lewisean conventions or Bratmanian shared activities are not at the foundations of law.