This book is based on articles, published in orientalist journals during the last twenty-five years and recently revised to make a consistent book and bring it up to date in a few places.

The first acknowledgement I should like to make is to my wife for her patience and her encouragement of my writing over such a long period.

Next, I wish to thank the institutions which have financed the free time which made these studies possible: namely, the University of Michigan and the State University of New York for sabbatical leaves and various research grants, as well as the Ford Foundation and the Simon E. Guggenheim Foundation which allowed me to extend sabbaticals on two occasions.

Thirdly, I acknowledge permissions granted to republish in book form the articles held in copyright by the following publishers: Scribner and Sons for articles in the Dictionary of the Middle Ages (2); the SUNY Press (Albany) (2); The Muslim World (3); Éditions de l'Institut Supérieur de Philosophic (Louvain); International Journal of Middle East Studies; Bruno Cassirer (Oxford); Caravan Press (Delmar, New York); Journal of the American Oriental Society; Studia Islamica (2); and Bulletin of the School of Oriental and African Studies (London). Full references to the original articles are given after this Preface, showing slight variations in the titles of three articles.

Fourthly, I am grateful to several secretaries at the University of Michigan and the State University of New York at Buffalo for their work in typing these articles.