Upon the common ground of rationalism and realism, Plato and Aristotle are complementary in temper, method, and principle. Plato's is the genius of inspiration and fertility, Aristotle's the genius of erudition, mastery, and synthesis. In form, Plato's is the gift of expression, Aristotle's the gift of arrangement. Plato was born and bred an aristocrat, and became the lover of the best--the uncompromising purist; Aristotle is middle-class, and limitlessly wide, hospitable, and patient in his interests. Thus while both are speculative and acute, Plato's mind is intensive and profound, Aristotle's extensive and orderly. It was inevitable, then, that Aristotle should find Plato one-sided. The philosophy of the ideal is not worldly enough to be true. It is a religion rather than a theory of reality. Aristotle, however, would not renounce it, but construe it that it may better provide for nature and history. This is the significance of his new terminology. Matter, to which Plato reluctantly concedes some room as a principle of degradation in the universe, is now admitted to good standing. _Matter_ or material is indispensable to being as its potentiality or that out of which it is constituted. The ideal, on the other hand, loses its exclusive title to the predicate of reality, and becomes the _form_, or the determinate nature which exists only in its particular embodiments. The being or _substance_ is the concrete individual, of which these are the abstracted aspects. Aristotle's "form," like Plato's "idea," is a teleological principle. The essential nature of the object is its perfection. It is furthermore essential to the object that it should strive after a higher perfection. With Aristotle, however, the reality is not the consummation of the process, the highest perfection in and for itself, but the very hierarchy of objects that ascends toward it. The highest perfection, or God, is not itself coextensive with being, but the final cause of being--that on account of which the whole progression of events takes place. Reality is the development with all of its ascending stages from the maximum of potentiality, or matter, to the maximum of actuality, or God the pure form. [Sidenote: The Aristotelian Philosophy as a Reconciliation of Platonism and Spinozism.]