Christianity was succeeded in the Orient by Mohammedanism, and this change led to even greater cultivation of Greek studies on the part of the Syrians. The Mohammedan Caliphs employed the Syrians as physicians. This was especially true of the Abbasid dynasty, who came into power in 750. When they succeeded to the Caliphate they raised Nestorian Syrians to offices of importance, and the latter under the patronage of their masters continued their studies of Greek science and philosophy and translated those writings into Syriac and Arabic. Among the authors translated were, Hippocrates and Galen in medicine, Euclid, Archimedes and Ptolemy in mathematics and astronomy, and Aristotle, Theophrastus and Alexander of Aphrodisias in philosophy. In many cases the Greek writings were not turned directly into Arabic but as the translators were Syrians, the versions were made first into Syriac, and then from the Syriac into Arabic. The Syrian Christians were thus the mediators between the Greeks and the Arabs. The latter, however, in the course of time far surpassed their Syrian teachers, developed important schools of philosophy, became the teachers of the Jews, and with the help of the latter introduced Greek philosophy as well as their own development thereof into Christian Europe in the beginning of the thirteenth century. We see now that the impulse to philosophizing came from the Greeks,--and not merely the impulse but the material, the matter as well as the method and the terminology. In the Aristotelian writings we find developed an entire system of thought. There is not a branch of knowledge dealing with fundamental principles which is not there represented. First of all Aristotle stands alone as the discoverer of the organon of thought, the tool which we all employ in our reasoning and reflection; he is the first formulator of the science and art of logic. He treats besides of the principles of nature and natural phenomena in the Physics and the treatise on the Heavens. He discusses the nature of the soul, the senses and the intellect in his "Psychology." In the "History of Animals" and other minor works we have a treatment of biology. In the Nikomachean and Eudemian Ethics he analyzes the meaning of virtue, gives a list and classification of the virtues and discusses the _summum bonum_ or the aim of human life. Finally in the Metaphysics we have an analysis of the fundamental notions of being, of the nature of reality and of God.