Introduction

In the centuries often characterized as 'post-antiquity', people, material objects, ideas, and knowledge continued to migrate across vast geographical spaces. Knowledge exchange took place in an increasingly heterogeneous political, economic, and cultural landscape, implying immense losses but also striking innovations. B. Gruendler's contribution analyzes the formation of a new professional group together with the formation of book-based forms of knowledge production and distribution in third/ninth-century Abbasid Baghdad. Knowledge in fact varies as widely as the challenges met by humans in different historical and cultural circumstances. As codified experience, knowledge has a cognitive or mental dimension that has traditionally been a focus of the history of ideas. Knowledge also has a systemic quality. Different elements of knowledge often relate to and depend on each other. Forms of knowledge vary along three basic dimensions: distributivity, systematicity, and reflexivity. Knowledge has a self-organizing quality that comes with its systematicity and reflexivity.