The fourth chapter traces out the implications of the second and third chapters for the organizing assumption of the Princeton School discussed in the first chapter. If Jewish merchants were educated as to the norms of Jewish commercial law and indeed chose to structure their economic relationships according to those norms, then the documents of the Geniza cannot be directly used as a proxy to describe commercial cooperation among Muslim merchants. The chapter introduces an alternative model for extrapolating from the Geniza documents to the broader Muslim world which takes into consideration Islamic and Jewish law as well as the surviving documentary evidence of Muslims and Jews alike.