If, then, it is not perfect in itself, each of the two would be granting perfection to the other. This is impossible, [for] (1) it would entail that each of the two things affects the other in a manner whose effect can arise only after the other has acted. The one cannot confer that perfection upon the other until it is itself perfect, yet it cannot be perfect until the other confers perfection upon it. This is impossible—just as it is impossible for this one not to exist until that one brings it into existence (2), while that one does not exist until this one brings it into existence.

If that other is a necessary being, perfect in itself and bringing perfection to another (3), while the other is a deficient necessary being that depends for its perfection upon that perfect being which brings perfection to others, then a part of it would depend upon the former. But anything of which a part depends upon another cannot, as a whole, be necessary in itself.

To clarify: that which is necessary in itself must either be a single thing having no parts or consist of parts. If it is a single thing having no parts, it cannot have one part—much less can it be said that one part of it depends upon another while another part does not. Nor can it be two things: one being the thing itself and the other its perfection.

If it is said that it consists of two or more parts, then that which is necessary would be the aggregate of those parts. It could not be necessary in itself unless the aggregate were necessary in itself. (* Whenever one part depends upon a cause separate from the aggregate, the aggregate cannot be necessary in itself. *) (4)