4. We should not be surprised at water extinguishing fire, or at fire destroying some other element. Even this element was introduced to existence by some other element, and it is not surprising that it should be destroyed, since it did not produce itself, and was introduced to existence only by the destruction of some other element (as thought Heraclitus and the Stoics[35]). Besides, the extinguished fire is replaced by another active fire. In the incorporeal heaven, everything is permanent; in the visible heaven, the totality, as well as the more important and the most essential parts, are eternal. The souls, on passing through different bodies, (by virtue of their disposition[36]), themselves change on assuming some particular form; but, when they can do so, they stand outside of generation, remaining united to the universal Soul. The bodies are alive by their form, and by the whole that each of them constitutes (by its union with a soul), since they are animals, and since they nourish themselves; for in the sense-world life is mobile, but in the intelligible world it is immobile. Immobility necessarily begat movement, self-contained life was compelled to produce other life, and calm being naturally exhaled vibrating spirit. OPPOSITION AMONG ANIMALS. Mutual struggle and destruction among animals is necessary, because they are not born immortal. Their origin is due to Reason's embracing all of matter, and because this Reason possessed within itself all the things that subsist in the intelligible World. From what other source would they have arisen? OPPOSITION AMONG HUMANS.