exclusively for natural philosophers, according to which it is that the existence and substance of things are examined, [for instance, whether the sun and the stars consist of matter and form,] and whether the sun is born or not born, whether it is living or lifeless, corruptible or incorruptible, whether it is regulated by Providence, and other questions of this kind.
The topic which examines into causes they say is also divisible into two parts; and with reference to one of its considerations, the investigations of physicians partake of it; according to which it is that they investigate the dominant principle of the soul, and the things which exist in the soul, and seeds, and things of this kind. And its other division is claimed as belonging to them also by the mathematicians, as, for instance, how we see, what is the cause of our appearance being reflected in a mirror, how clouds are collected, how thunder is produced, and the rainbow, and the halo, and comets, and things of that kind.
LXVIII. They think that there are two general principles in the universe, the active and the passive. That the passive is matter, an existence without any distinctive quality. That the active is the reason which exists in the passive, that is to say, God. For that he, being eternal, and existing throughout all matter, makes everything. And Zeno, the Cittiæan, lays down this doctrine in his treatise on Essence, and so does Cleanthes in his essay on Atoms, Chrysippus in the first book of his Investigations in Natural Philosophy, towards the end, Archedemus in his work on Elements, and Posidonius in the second book of his treatise on Natural Philosophy. But they say that principles and elements differ from one another. For that the one had no generation or beginning, and will have no end; but that the elements may be destroyed by the operation of fire. Also, that the elements are bodies, but principles have no bodies and no