necessary existence and confined to created beings, entail nonexistence—or, at the very least, susceptibility to nonexistence. For everything that falls outside necessary existence is susceptible to nonexistence; indeed, it is nonexistent at one time and existent at another.

Thus, it becomes clear that if the cause of seeing is not existence or its necessary concomitants, it must entail nonexistence—or, if you prefer, susceptibility to nonexistence. This exhaustive division between affirmation and negation disposes of the objections raised here.

Accordingly, the cause of seeing visible things cannot be something that requires nonexistence or susceptibility to it, because being nonexistent or susceptible to nonexistence cannot give rise to something that exists. Seeing is a positive reality, and a positive reality cannot have a privative cause. This is self-evident to anyone who grasps it.

Yet an absence may entail the existence of something, as when the absence of impediments entails the completeness of a cause through the presence of its conditions, which are parts of the complete cause. The effect is then attributed to that absence, but this is an attribution to an incomplete cause; and an incomplete cause constitutes a part and a condition of the cause