Compiled in 987–88, Ibn al-Nadim's work al-Fihrist (The Catalogue) needs little introduction to scholars of Middle Eastern and Islamic history. Countless specialized studies have used the Fihrist as a source of data. Because it includes the titles of a large number of works that are no longer extant, as well as biographical information on little-known early authors, it throws light on otherwise obscure facets of medieval Islamic intellectual history in many fields. Choice anecdotes, such as the account of al-Maءmun's (r. 813–33) conversation with Aristotle in a dream, considered to have triggered the translation movement, have been quoted in numerous studies. Little attention has been paid, however, to Ibn al-Nadim as a thinker, despite the fact that the Fihrist, like Dewey's decimal system, is as much an exercise in mapping out the organization of human knowledge as a simple inventory of book titles. The following remarks focus first on the methods Ibn al-Nadim adopted in compiling the Fihrist and second on the arguments he makes about the history of Islamic sciences, in many cases not explicitly but through order, presentation, and the calculus of inclusion and exclusion, emphasis and de-emphasis. Particular attention will be paid to the Islamic legal madhhabs and theological schools. Determining Ibn al-Nadim's views on these topics, as an Imami Shiʿi and Muʿtazili theologian, promises to provide a better understanding of his conception of the Islamic sciences, the overall message of his work, and Islamic intellectual history itself.