Plato never went so far as to reduce his great discoveries and intuitions in every department of science to a complete and connected whole, being averse, on scientific and ethical grounds alike, from the dogmatic definition inseparable from any systematic treatise. This Aristotle did, dividing the whole body of philosophy under three principal heads (theoretical, practical, and poetical) and distinguishing subdivisions (logic, physics, metaphysics, ethics, and politics, and so forth) within these divisions by strongly marked lines of demarcation and methods rigorously exact. He is a Platonist in all things and feels himself so to be. Even where he displays most independence, as in the development of syllogisms or in biology, it is impossible to overlook his indebtedness to the bold speculations of the master. If the whole work of Plato’s life and of his scholars between 388 and 348 had been preserved to us, the ultimate connection between Aristotle and the researches of the Academy would probably be even more evident than it is. Nevertheless there is a marked difference between the speculations of these two great philosophers. Plato wholly dissevered the Universal and Essential in things from the Terrestrial and placed it in a heaven beyond the earth. Aristotle repudiates this transcendentalism all along the line. The Universal cannot exist without the archetype, the essence must be immanent in it. Hence the individual is the only true Substantive, containing Substance and Matter. This opposition of opinion concerning “Universalia” is, as is well known, the starting-point of mediæval Scholasticism (Nominalism, Realism).