Proof.--The effort for self--preservation is the essence of a thing (III. vii.); therefore, if any virtue could be conceived as prior thereto, the essence of a thing would have to be conceived as prior to itself, which is obviously absurd. Therefore no virtue, &c. Q.E.D. Corollary.--The effort for self--preservation is the first and only foundation of virtue. For prior to this principle nothing can be conceived, and without it no virtue can be conceived. PROP. XXIII. Man, in so far as he is determined to a particular action because he has inadequate ideas, cannot be absolutely said to act in obedience to virtue; he can only be so described, in so far as he is determined for the action because he understands. Proof.--In so far as a man is determined to an action through having inadequate ideas, he is passive (III. i.), that is (III. Deff. i., and iii.), he does something, which cannot be perceived solely through his essence, that is (by IV. Def. viii.), which does not follow from his virtue. But, in so far as he is determined for an action because he understands, he is active; that is, he does something, which is perceived through his essence alone, or which adequately follows from his virtue. Q.E.D. PROP. XXIV. To act absolutely in obedience to virtue is in us the same thing as to act, to live, or to preserve one's being (these three terms are identical in meaning) in accordance with the dictates of reason on the basis of seeking what is useful to one's self. Proof.--To act absolutely in obedience to virtue is nothing else but to act according to the laws of one's own nature. 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. vii.); from this alone, and not from the essence of anything else, it necessarily follows (III. vi.) that everyone endeavours to preserve his being. Moreover, this proposition is plain from IV. xxii. Coroll., for if a man should endeavour to preserve his being for the sake of anything else, the last--named thing would obviously be the basis of virtue, which, by the foregoing corollary, is absurd. Therefore no one, &c. Q.E.D. PROP. XXVI. Whatsoever we endeavour in obedience to reason is nothing further than to understand; neither does the mind, in so far as it makes use of reason, judge anything to be useful to it, save such things as are conducive to understanding.