But we only act, in so far as we understand (III.

iii.): therefore to act in obedience to virtue is in us nothing else but to act, to live, or to preserve one's being in obedience to reason, and that on the basis of seeking what is useful for us (IV.

xxii.
Coroll.).

Q.E.D.
PROP.XXV.

No one wishes to preserve his being for the sake of anything else.
Proof .-- The endeavour, wherewith everything endeavours to persist in its being, is defined solely by the essence of the thing itself (III.