In a volume celebrating the scholarship of Ed Sanders, Shaye Cohen considered the evidence of Greek and Roman writings for Sanders's notion of “common Judaism.” There he makes a point important for my effort here: These writers mention things distinctive to Jews, but have almost nothing to say about what was common across the Mediterranean. Thus, for instance, they say nothing about Jewish hymns and prayers. But what exactly is the price to pay for characterizing Jewish religion by difference only?

Ed Sanders's idea of common Judaism has been a hit, albeit with a number of dissenters. The idea beautifully expresses intuitions underlying conceptions of Jewish and Christian origins that have been and still are normative for many. In my estimation, there is clearly something right about common Judaism. There were, for instance, social mechanisms that allowed for ethnic-religious self-identification and identification by others. But the idea contradicts much of the scholarship about social groups that has become dominant in the social sciences, parts of the humanities and the mind sciences in the last several decades. The academy is in the midst of a major revolution in thinking about social groups. I will briefly discuss why the common belief/practice model that “common Judaism” assumes cannot adequately deal with the dynamics of ancient Mediterranean religion.

Psychology and other fields have shown dramatically that we know far less than we think we know. With unrealistic confidence individuals hold fragmentary outlines of knowledge and what is known varies greatly across individuals in a population. This overconfidence has in many ways served our species well. The unfounded confidence has made us bold about acting and going forward even when we really do not know. The mentally efficient fragments and outlines often pay off because they allow us just enough information to discover where to go for types of expertise or to technologies of knowledge for answers. Brains/minds with intrinsic limits can not survive unless they are efficient and adapted to the resources of their social environment. The key resource of social environments comes in that many people in any culture are experts in some small corner of knowledge.