With Maimonides we reach the high water mark of mediæval Jewish philosophy. He was by far the most comprehensive mind of mediæval Jewry, and his philosophy was the coping stone of a complete system of Judaism. In his training and education he embraced all Jewish literature, Biblical and Rabbinic, as well as all the science and philosophy of his day. And his literary activity was fruitful in every important branch of study. He was well known as a practicing physician, having been in the employ of the Caliph's visier at Cairo (Fostat), and he wrote on medical theory and practice. He was versed in mathematics and astronomy, and his knowledge of these subjects served him in good stead not merely as an introduction to theology and metaphysics, but was of direct service in his studies and writings on the Jewish calendar. It goes without saying that he knew logic, for this was the basis of all learning in mediæval times; but in this branch, too, Maimonides has left us a youthful treatise,[247] which bears witness to his early interest in science and his efforts to recommend its study as helpful to a better understanding of Jewish literature. But all these activities and productions were more or less side issues, or preparations for a _magnum opus_, or rather _magna opera_. From his youth we can trace the evident purpose, not finally completed until toward the end of his brilliant and useful career,--the purpose to harmonize Judaism with philosophy, to reconcile the Bible and Talmud with Aristotle. He was ambitious to do this for the good of Judaism, and in the interest of a rational and enlightened faith. Thus in his commentary on the Mishna,[248] the earliest of his larger works, he had already conceived the idea of writing a composition of a harmonizing nature, _viz._, to gather all the homiletical disquisitions of the Talmud (the "derashot") and explain them in a rationalistic manner so as to remove what appears on the surface to be offensive to sound reason. But instead of proceeding at once to the performance of this cherished object of his philosophic ambition, he kept it in his bosom, brooding over it during a life of intense literary and practical activity, until it was in the end matured and brought to fruition in a manner quite different from that at first intended. The book explanatory of the Rabbinic legends was given up for reasons which will appear later. But the object that work was to realize was carried out in a much more effective manner because it was delayed, and was published toward the end of his life as the systematic and authoritative pronouncement of the greatest Jew of his time. The "Guide of the Perplexed" would not have attracted the attention it did, it would not have raised the storm which divided Jewry into two opposed camps, if it had not come as the mature work of the man whom all Jewry recognized as the greatest Rabbinic authority of his time. Others had written on philosophy before Maimonides.