Their account is in full agreement with Aristotle's description of Plato's metaphysical doctrine. In "Metaphysics" he writes: "Now since the Forms are the causes of everything else, he Plato supposed that their elements are the elements of all things. Accordingly the material principle is the Great and Small the Dyad, and the essence is the One (), since the numbers are derived from the Great and Small by participation in the One". "From this account it is clear that he only employed two causes: that of the essence, and the material cause; for the Forms are the cause of the essence in everything else, and the One is the cause of it in the Forms. He also tells us what the material substrate is of which the Forms are predicated in the case of sensible things, and the One in that of the Forms—that it is this the duality (the Dyad, ), the Great and Small (). Further, he assigned to these two elements respectively the causation of good and of evil".