This article highlights the importance of the notions of radical uncertainty and social structures when studying the concrete functioning of markets and the different forms of competition that take place among entrepreneurs. The article refers to two theoretical currents which take these notions seriously in their respective research project: post-Keynesian economics and structural economic sociology. The theoretical argument is illustrated with empirical data from a survey of 300 restaurants’ owners in and around Lille (France). JEL codes: L16, L14, D43, D8