XVIII. Besides the visionary wise people, or those which are such in appearance only, there are others who have credit given them for being men of profound knowledge, merely from the mistakes and misapprehensions of others. He who studies logic and metaphysics in the schools, together with those other matters, which under the denomination of philosophy are taught there, notwithstanding the sounding names, of these faculties, and his being supposed to know every thing, in reality, knows but little more than nothing. It is commonly said, that such a man is a great philosopher, when in truth he is no philosopher at all, either great or little. All the ten categorical principles, together with the whole contents of the eight books on physics, and their two adjuncts _on generation and corruption_, put into a logical alembic, would not produce a drop of true philosophical spirit, that would assist us to explain the most vulgar phenomenon in the sensible world. The Aristotelic ideas, have no more to do with physics, than the Platonic ones; and the physics of the schools, are pure metaphysics. All that the Peripatetics have hitherto written or disputed concerning motion, has not determined, what is the line of reflection, by which a ball returns back that is struck against a wall, or what is the degree of velocity, with which a heavy body descends by an inclined plane. He who by the ordinary metaphysical reasonings, thinks to attain a true knowledge of nature, is as mad, as he who should fancy himself master of the world, because he is possessed of a map of it. XIX. The great advantage of these philosophers in name, if in the schools they manage with dexterity the rules of science, consists in this, that in virtue of the four species or rudiments of theology or medicine they acquire there, they are enabled to dazzle the eyes of mankind, and to pass in the world, for great theologians and doctors of physic. With respect to theology, the mistake in this matter is not so great; but with regard to medicine, it cannot be greater. By the rule, _Ubi desinit physicus, incipit medicus_, it seems as if it should follow of course, that a good philosopher is easily made a good doctor of physic. Upon this supposition, when people see a practising physician, who has twenty syllogisms at his fingers ends, ready to explain and demonstrate, whether privation is a principle annexed to a natural entity, or whether the united mass or the whole, can be of a distinct or different texture from the parts, they fancy he is possessed of all the requisites and recommendations, that are necessary to establish and fix him as a most able, or first rate man in his profession.