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.
Proof.--The effort for self--preservation is nothing else but the essence of the thing in question (III. vii.), which, in so far as it exists such as it is, is conceived to have force for continuing in existence (III. vi.) and doing such things as necessarily follow from its given nature (see the Def. of Appetite, III. ix. note). But the essence of reason is nought else but our mind, in so far as it clearly and distinctly understands (see the definition in II. xl. note. ii.); therefore (II. xl.) whatsoever we endeavour in obedience to reason is nothing else but to understand. Again, since this effort of the mind wherewith the mind endeavours, in so far as it reasons, to preserve its own being is nothing else but understanding; this effort at understanding is (IV. xxii. Coroll.) the first and single basis of virtue, nor shall we endeavour to understand things for the sake of any ulterior object (IV. xxv.); on the other hand, the mind, in so far as it reasons, will not be able to conceive any good for itself, save such things as are conducive to understanding.
PROP. XXVII. We know nothing to be certainly good or evil, save such things as really conduce to understanding, or such as are able to hinder us from understanding.
Proof.--The mind, in so far as it reasons, desires nothing beyond understanding, and judges nothing to be useful to itself, save such things as conduce to understanding (by the foregoing Prop.). But the mind (II. xli., xliii. and note) cannot possess certainty concerning anything, except in so far as it has adequate ideas, or (what by II. xl. note, is the same thing) in so far as it reasons. Therefore we know nothing to be good or evil save such things as really conduce, &c. Q.E.D.