 Finally, there is ample evidence that people’s perceptions may change very rapidly. Since in this framework norms are defined as shared perceptions about group beliefs, one would expect that—whenever all members of a group happen to believe that others have changed their beliefs about core membership rules—the very norms that define membership will change. The study of fashion, fads and speculative bubbles clearly shows that there are some domains in which rapid (and possibly disruptive) changes of collective expectations may occur; it is, however, much less clear what sort of norms are more likely to be subject to rapid changes (think of dress codes rather than codes of honor). The social identity view does not offer a theoretical framework for differentiating these cases: although some norms are indeed related to group membership, and thus compliance may be explained through identity-validation mechanisms, there appear to be limits to the social identity explanation.