In this paper, a model of norms as cognitive objects is applied to establish connections between social conventions and prescriptions. Relevant literature on this issue, especially found in AI and the social sciences, will be shown to suffer from a dychotomic view: a conventionalistic view proposed by rationality and AI scientists; and a prescriptive view proposed by some philosophers of law (Kelsen 1934/1979, Hart 1961, Ross, 1958).In the present work, the attempt is made to fill the gap between these views (...) by putting forward a hypothesis concerning the process from perceived behavioural regularities to normative assumptions. The emergence of norms will be here seen as intrinsically intertwined with the emergence of normative beliefs. Unlike that assumed by the conventionalistic sight, the process of emergence is seen as a non-continuous phenomenon. A given behavioural regularity will be argued to give rise to a normative belief if and as long as that regularity is believed to be prescribed within the community. Two corollaries of this hypothesis will be examined: (1) unlike that implied by the conventionalistic view, the spreading of norms is not only due to a passive behavioural social influence (imitation) but also to an active cognitive one (the spreading of normative wants and beliefs); (2) unlike that assumed by the prescriptive view, a norm is not necessarily explicitly and deliberately issued by some normative authority, but is grounded upon the norm-addressees' beliefs that they are generally prescribed to comply with it. (shrink)