Medieval Jewish philosophy
At university I studied philosophy and began writing a dissertation in medieval Jewish philosophy at the École Pratique des Hautes Études, under the supervision of Georges Vajda.
In the Middle Ages, "philosophy" referred to explanations of the world, based on human reason, of the sort that first appeared in Greece, with Plato and Aristotle (5th and 4th centuries BCE). Today we call this "science". These texts, translated into Arabic (starting in the 9th century CE) and expounded by Arabophone scholars, covered the entire domain of the sciences known then. They were read and adopted by members of all faiths in the Islamic world. The Jews referred to them as "external wisdom," because they came from another source than the revealed Law. The Middle Ages were marked by endless controversies between philosophers and the partisans of a purely religious tradition. These grew more heated when Hebrew translations made these texts available to European Jews ignorant of Arabic. The adherents of philosophy proliferated in Provence, Spain, and Italy; but the attraction of mysticism also increased. By the time Hebrew printing widespread (in the 16th century), philosophy had gone out of fashion. The presses preferred to publish works of kabbalah or other mystic disciplines and, in philosophy, only the best-known authors.
The gap between the number of philosophical manuscripts and the number of printed treatises was never closed. Many philosophers of the 13th to 15th centuries remained unknown to most scholars. Because only the greatest authors - such as Saadia, Maimonides, Gersonides, Crescas, and a few others - were brought to press, they had the histories of Jewish philosophy more or less to themselves.
Manuscripts provided the basis of roughly half of the book which gives an overview of medieval Jewish philosophy (bibl. book 3, published in Hebrew 1975 and followed by editions in French, English, Italian, Hungarian, and Russian, books 8-12). Practically all of the articles I published thereafter (bibl. article 25 etc.) dealt with texts that were still unpublished at the time. My study of unpublished Jewish philosophical treatises has continued throughout my career and still interests me today. During the last years, the situation has much improved: many young colleagues have published quite a number of good editions based on manuscripts.
Manuscripts are also the sources of new knowledge in the teaching of philosophy: we recently learnt that institutions dedicated only to the teaching of philosophy (yeshivot hokhmot hitsoniot) were in existence in Spain during the 15th century.