The paper addresses the problem on the source of epistemic normativity of science from a social-historical approach. Based on the communitarian model of linguistic practices, it argues that scientific norms are institutions, ie stable patterns of collective behavior which are generated and constituted through the historical development of scientific investigation. First it gives an account of the normativity of linguistic practices. Then it characterizes the normativity of science insofar as it is an institution concerned to produce knowledge of