Gillett has especially aided me with criticism and suggestions on the terminology of scholastic theol ogy. Dr. Talcott Williams, of Philadelphia, illumined for me the Idrisid movement in North Africa. One complete sentence on p. 85 I have conveyed from a kindly notice in The Nation of my inaugural lecture on the development of Muslim Jurisprudence. Fi nally, and above all, I am indebted to my wife for much patient labor in copying and for keen and ln minous criticism in planning and correcting. With thanks to her this preface may fitly close.