There was no examination for admission as an undergraduate to Oxford, but a knowledge of Latin with some skill in speaking Latin was a necessary background. The students came from all backgrounds. Some had their expenses paid by their parents, while others had the patronage of a churchman, a religious house, or a wealthy layman. They studied the "liberal arts", which derived its name from "liber" or free, because they were for the free men of Rome rather than for the economic purposes of those who had to work. The works of Greek authors such as Aristotle were now available; the European monk Thomas Aquinas had edited Aristotle's works to reconcile them to church doctrine. He opined that man's intellectual use of reason did not conflict with the religious belief that revelation came only from God, because reason was given to man by God. He shared Aristotle's belief that the earth was a sphere, and that the celestial bodies moved around it in perfect circles. Latin learning had already been absorbed without detriment to the church. A student at Oxford would become a master after graduating from a seven year course of study of the seven liberal arts: [grammar, rhetoric (the source of law), Aristotelian logic (which differentiates the true from the false), arithmetic, including fractions and ratios, (the foundation of order), geometry, including methods of finding the length of lines, the area of surfaces, and the volume of solids, (the science of measurement), astronomy (the most noble of the sciences because it is connected with divinity and theology), music and also Aristotle's philosophy of physics, metaphysics, and ethics; and then lecturing and leading disputations for two years. He also had to write a thesis on some chosen subject and defend it against the faculty. A Master's degree gave one the right to teach. Further study for four years led to a doctorate in one of the professions: theology and canon or civil law.