P40: The more perfection each thing has, the more it acts and the less it is acted on; and conversely, the more it acts, the more perfect it is.

Dem.: The more each thing is perfect, the more reality it has (by IID6), and consequently (by IIIP3 and P3 S), the more it acts and the less it is acted on. This Demonstration indeed proceeds in the same way in reverse, from which it follows that the more a thing acts, the more perfect it is, q.e.d.

Cor.: From this it follows that the part of the Mind that remains, however great it is, is more perfect than the rest.

For the eternal part of the Mind (by P23 and P29) is the intellect, through which alone we are said to act (by IIIP3). But what we have shown to perish is the imagination (by P21), through which alone we are said to be acted on (by IIIP3 and the gen. Def. Aff.). So (by P40), the intellect, however extensive it is, is more perfect than the imagination, q.e.d.

Schol.: These are the things I have decided to show concerning the Mind, insofar as it is considered without relation to the Body’s existence. From them—and at the same time from IP21 and other things—it is clear that our Mind, insofar as it understands, is an eternal mode of thinking, which is determined by another eternal mode of thinking, and this again by another, and so on, to infinity; so that together, they all constitute God/Nature’s eternal and infinite intellect.