E4P56D
Demonstration — Part IV
Latin
Primum virtutis fundamentum est suum esse conservare (per corollarium propositionis 22 hujus) idque ex ductu rationis (per propositionem 24 hujus). Qui igitur se ipsum ignorat, omnium virtutum fundamentum et consequenter omnes virtutes ignorat. Deinde ex virtute agere nihil aliud est quam ex ductu rationis agere (per propositionem 24 hujus) et qui ex ductu rationis agit, scire necessario debet se ex ductu rationis agere (per propositionem 43 partis II); qui itaque se ipsum et consequenter (ut jam jam ostendimus) omnes virtutes maxime ignorat, is minime ex virtute agit hoc est (ut ex definitione 8 hujus patet) maxime animo est impotens atque adeo (per propositionem præcedentem) maxima superbia vel abjectio maximam animi impotentiam indicat. Q.E.D.
English (Elwes 1883)
The first foundation of virtue is self--preservation (IV. xxii. Coroll.) under the guidance of reason (IV. xxiv.). He, therefore, who is ignorant of himself, is ignorant of the foundation of all virtues, and consequently of all virtues. Again, to act virtuously is merely to act under the guidance of reason (IV. xxiv.): now he, that acts under the guidance of reason, must necessarily know that he so acts (II. xliii.). Therefore he who is in extreme ignorance of himself, and consequently of all virtues, acts least in obedience to virtue; in other words (IV. Def. viii.), is most infirm of spirit. Thus extreme pride or dejection indicates extreme infirmity of spirit. Q.E.D.
Modern English
The first foundation of virtue is preserving one's own being (E4P22C), and doing so under the guidance of reason (E4P24). Whoever is ignorant of himself is therefore ignorant of the foundation of all virtues, and consequently of all virtues.
To act from virtue is simply to act under the guidance of reason (E4P24), and whoever acts under the guidance of reason must necessarily know that he so acts (E2P43). So whoever is most ignorant of himself — and therefore, as just shown, most ignorant of all virtues — acts least from virtue, that is (E4D8), is most powerless in mind. Extreme pride or dejection therefore indicates extreme powerlessness of mind. Q.E.D.