The five chapters of this book were written during the years 1976-81. Some of them were presented in condensed form at various conferences, collo- quia and seminars. The reactions and criticisms they evoked have been incorporated where appropriate. Thus Chapters 2 and 4 were read at UEAI congresses held respectively in Aix-en-Provence (1976) and Am- sterdam (1978). Chapter 2 was also introduced at a SOAS seminar in London in 1977 as well as at a seminar organized by the Institute for
Advanced Studies of the Hebrew University in Jerusalem, where, during a
year's stay (I979-80), I had the opportunity to discuss also Chapter 3 and
4.