In glancing at the titles of Philo's works, it might appear easy to define the nature of God and the cosmos. This is because two of his works, Quod Deus sit immutabilis (On the Unchangeableness of God) and De aeternitate mundi (On the Eternity of the World), have titles that are quite pertinent to these topics, and might lead one to believe that these works provide complete and definitive information. But this is not the case. The Quod Deus deals essentially with the constancy and irrevocability of divine judgment, and does not treat the question of God's nature. The De aeternitate on the other hand appears to be a kind of scholastic work in which two opposing theses are contrasted with each other, not in order to set out the views of the author but rather to put on display his competence and erudition in the philosophical disciplines. However, the work seems to have been handed down in incomplete form, and the part that survives contains a thesis that is irreconcilable with the thought of Philo taken as whole. Therefore, to follow the path indicated by the titles of his works will not bring us to heart of the subject of this chapter, and it might even lead us astray. For Philo never formulated a theology that was independently forged, or a systematic and autonomous physics. There is a good reason for this, as will become immediately apparent. To discuss God while taking the world as a point of departure is a well-established method in philosophical study. It is enough to consider the path taken by Aristotle who, starting from the dynamic character of the cosmos, arrives at the idea of God as unmoved mover, or, starting from the imperfection of the world, arrives at the perfection of God conceived as final cause. But to proceed in the opposite direction, that is, to discuss the world while taking God and the divine as the point of departure, is an equally legitimate method and can be understood to correspond to the Platonic (and latter Middle Platonic and Neoplatonic) position.