The Summa Contra Gentiles of Saint Thomas Aquinas: The Third Book (Part II, Chapters 84-163)

THAT THE HEAVENLY BODIES DO NOT IMPRESS ON OUR INTELLECT

From what has been said it is at once clear that the heavenly bodies cannot be the causes of things concerning our intellect. For it has already been shown that the order of divine providence requires the lower things to be ruled and moved by the higher. Now the intellect, in the natural order, surpasses all bodies: as we have proved already. Consequently heavenly bodies cannot act directly on the intellect. Therefore they cannot be the direct cause of things concerning the intellect.

Again. No body acts except through movement, as is proved in 8 Phys. vi. Now things that are immovable are not caused by movement: because nothing is the result of the movement of an agent except through the agent moving the patient, while the latter is moved. Consequently things that are wholly outside movement cannot be caused by the heavenly bodies. But things concerning the intellect are wholly outside movement properly speaking, as the Philosopher states (7 Phys. iii.): in fact the soul becomes prudent and wise through being free from movement, as he says in the same place. It is not possible, therefore, that the heavenly bodies be the direct cause of things concerning the intellect.