What are the conditions that must be present in order for fads to arise in a regional sphere and national level?
In analyzing the historical value of fads and fashions, I would say that there are some specific conditions that have to be met. One should be that the fad has to be embraced on a large enough level to be absorbed by as many people as possible. In this widened embrace is some level of contingency that is shared by many, which can be the basis for historical analysis. At the same time, the fad or fashion has to reflect something of the time period which is uniquely and distinctive. This makes the analysis of the fad or fashion something worthy of noting both at the time and afterwards. Finally, the fad or fashion might contain both surface and symbolic meaning and the historian has to be willing to see both.
Recent American History can be a great guide to this process. For example, the Disco fad can be seen as something "surface" within the 1970s,or can feature a deeper level of meaning. The same can be done to flapper fashion of the 1920s, the rise of 1960s Counter Culture, as well as to a more modern setting as with Grunge in the 1990s or 1980s Rap. These elements can be analyzed as more than mere fads or fashions,but can reveal more about the nation and the people of that time period.