|This paper argues that both Marx and Hayek objected to the dichotomy between physis and nomos, and offered concepts which integrate, or mediate between, the two. Marx's value forms and Hayek's rules aim to grasp something neither purely natural nor purely artificial or social, but "socially natural". Value forms and rules are natural in the sense that they pre-exist the agents and are taken by the agents as given. On the other hand, forms and rules are social in that productions relations or spontaneous order are reproduced as the unintended consequences of the agents' using forms or following rules. Thus value forms and rules stand as links between agents and production relations or spontaneous order.