The physics of the Stoics started from the fundamental [398] proposition that in the universe of things there were two elements--the active and the passive. {233} The latter was Matter or unqualified existence; the former was the reason or qualifying element in Matter, that is, God, who being eternal, is the fashioner of every individual thing throughout the universe of matter. God is One; He is Reason, and Fate, and Zeus. In fact all the gods are only various representations of His faculties and powers. He being from the beginning of things by Himself, turneth all existence through air to water. And even as the genital seed is enclosed in the semen, so also was the seed of the world concealed in the water, making its matter apt for the further birth of things; then first it brought into being the four elements--fire, water, air, earth. For there was a finer fire or air which was the moving spirit of things; later and lower than this were the material elements of fire and air. It follows that the universe of things is threefold; there is first God Himself, the source of all character and individuality, who is indestructible and eternal, the fashioner of all things, who in certain cycles of ages gathers up all things into Himself, and then out of Himself brings them again to birth; there is the matter of the universe whereon God works; and thirdly, there is the union of the two. Thus the world is governed by reason and forethought, and this reason extends through every part, even as the soul or life extends to every part of us. The universe therefore is a living thing, having a {234} soul or reason in it. This soul or reason one teacher likened to the air, another to the sky, another to the sun. For the soul of nature is, as it were, a finer air or fire, having a power of creation in it, and moving in an ordered way to the production of things. [399] The universe is one and of limited extension, being spherical in form, for this is the form which best adapts itself to movement. Outside this universe is infinite bodiless space; but within the universe there is no empty part; all is continuous and united, as is proved by the harmony of relation which exists between the heavenly bodies and those upon the earth. The world as such is destructible, for its parts are subject to change and to decay; yet is this change or destruction only in respect of the qualities imposed upon it from time to time by the Reason inherent in it; the mere unqualified Matter remains indestructible. [408]