XII. Farther still, if they say that every soul is corruptible, it would be requisite that all things should have long since perished. But if they assert that one soul is corruptible, and another not, as for instance, that the soul of the universe is immortal, but ours not, it is necessary that they should assign the cause of this difference. For each is the cause of motion, and each lives from itself. Each, likewise, comes into contact with the same things by the same power, intellectually perceiving the natures in the heavens, and also those that are beyond the heavens, investigating everything which has an essential subsistence, and ascending as far as to the first principle of things. To which may be added, that it is evident the soul gave being to itself prior to the body, from its ability of apprehending what each thing is, by itself, from its own inherent spectacles, and from reminiscence. And from its employing eternal sciences, it is manifest that it is itself perpetual. Besides, since everything which can be dissolved receives composition, hence, so far as a thing is a composite, it is naturally adapted to be dissolved. But soul being one simple energy, and a nature characterized by life, cannot be corrupted as a composite. Will it, therefore, through being divided and distributed into minute parts, perish ? Soul, however, is not, as we have demonstrated, a certain bulk or quantity. May it not, therefore, through being changed in quality, be corrupted ? Change in quality however which corrupts takes away form, but leaves the subject matter. But this is the passion of a composite. Hence, if it is not possible for the soul to be corrupted according to any of these modes, it is necessarily incorruptible.