His books "On the Good" ("Peri Tagathou - Περὶ Τἀγαθοῦ") seem to have been of a better kind; in them he had minutely explained, mainly in opposition to the Stoics, that existence could neither be found in the elements because they were in a perpetual state of change and transition, nor in matter because it is vague, inconstant, lifeless, and in itself not an object of our knowledge; and that, on the contrary, existence, in order to resist the annihilation and decay of matter, must itself rather be incorporeal and removed from all mutability, in eternal presence, without being subject to the variation of time, simple and imperturbable in its nature by its own will as well as by influence from without. True existence is identical with the first god existing in and by itself, that is, with good, and is defined as spirit ("nous"). But as the first (absolute) god existing in itself and being undisturbed in its motion, could not be creative ("demiurgikos - δημιουργικός"), he thought that we must assume a second god, who keeps matter together, directs its energy to it and to intelligible essences, and imparts its spirit to all creatures; its mind is directed to the first god, in whom it beholds the ideas according to which it arranges the world harmoniously, being seized with a desire to create the world. The first god communicates its ideas to the second, without losing them itself, just as we communicate knowledge to one another, without depriving ourselves of it. In regard to the relation existing between the third and second god, and to the manner in which they also are to be conceived as one (probably in opposition to the vague duration of matter), no information can be derived from the fragments which have come down to us.