The normative dimension is essential in social life. In this work, it is claimed that a crucial aspect of the normative mechanism is the normative request, which plays a fundamental role in the spreading of normative behaviours. A social norm is here defined to be such only if it is associated with a normative request (want) that it be observed. However, within both the rational decision theory and, more recently, the multi agent systems research, norms have so far been viewed essentially as conventions. Little reference, if any, has been made to the prescriptive character of norms, that is, to the normative requests.