XLI. Plato lays down two primary causes or principles of all things, God and matter, which he also calls mind, and the cause. And he defines matter as something without shape and without limitation, and says that from it all concretions arise. He affirms also that as it was moving about at random, it was brought by God into one settled place, as God thought order better than disorder; and that this nature is divided into four elements, fire, water, air, and earth, of which the world itself and everything in it was made. But he says that the earth is the only thing that is unchangeable, as he considers the cause to be the difference of the figures of which it is composed; for he says that the figures of the others are homogeneous; for that they are all composed equally of scalene triangles. The figure of the earth, however, is peculiar to itself; for the element of fire is a pyramid; of air, an octagon; of water, an eicosagon; and of the earth, a cube; owing to which these things cannot be changed into earth, nor earth into them. He teaches also that these elements are not separated so as to occupy each a peculiar and distinct place; for the spherical motion collects and compresses all the small things towards the centre, and the small things separate the great ones, on which account the species, as they change, do also change their positions. Moreover he asserts that the world is one, and has been produced, since it has been made by God, in such a manner as to be an object of sensation. And he considers it endowed with life, because that which is so endowed, is superior to that which is not, and it must be the production of the most excellent producer. It is also one, and illimitable; because the model after which it was made was one; and it is spherical, because its creator was of that form; for it also contains all other animals, and God who made it comprises all forms. And it is smooth, and has no instruments whatever all round it, because it has no need of any. But the whole world remains imperishable, because it cannot be resolved into God; and God is the cause of universal production, because it is the nature of the good to be productive of good; and the best is the cause of the production of the heaven; for the best of all productions can have no other cause than the best of all intelligible existences. And since God is of that character, and since heaven resembles the best, inasmuch as it is at least the most beautiful of all things, it cannot be like anything else that is produced, except God.