What is a social norm? A discussion of three analytical approaches

In this paper we compare the definitions of social norm proposed by standard Rational Choice Theory, Cristina Bicchieri and Jon Elster. We try to determine how similar or different they are. As long as they present some differences, we try to establish which captures better the very nature of the phenomena that we usually name "social norm" and which provides us with a concept (or concepts) more precise and productive and more easily useable in explicative models. In our opinion, Jon Elster's classification between moral, quasi-moral and social norms is the more successful in this respect. In spite of the fact that Jon Elster does not plan to use their concepts in formal mathematical models with predictive purposes, there is not anything inherent in them which prevents this use. On the other hand, the precision of these concepts makes them especially useful to be used in social mechanism models which let us propose causal, informative and parsimonious explanations of real concrete cases.