E4P31C
Corollary — Part IV
Latin
Hinc sequitur quod quo res aliqua magis cum nostra natura convenit, eo nobis est utilior seu magis bona et contra quo res aliqua nobis est utilior, eatenus cum nostra natura magis convenit. Nam quatenus cum nostra natura non convenit, erit necessario a nostra natura diversa vel eidem contraria. Si diversa, tum (per propositionem 29 hujus) neque bona neque mala esse poterit; si autem contraria, erit ergo etiam ei contraria quæ cum nostra natura convenit hoc est (per propositionem præcedentem) contraria bono seu mala. Nihil igitur nisi quatenus cum nostra natura convenit, potest esse bonum atque adeo quo res aliqua magis cum nostra natura convenit, eo est utilior et contra. Q.E.D.
English (Elwes 1883)
Hence it follows, that, in proportion as a thing is in harmony with our nature, so is it more useful or better for us, and vice versa, in proportion as a thing is more useful for us, so is it more in harmony with our nature. For, in so far as it is not in harmony with our nature, it will necessarily be different therefrom or contrary thereto. If different, it can neither be good nor bad (IV. xxix.); if contrary, it will be contrary to that which is in harmony with our nature, that is, contrary to what is good--in short, bad. Nothing, therefore, can be good, except in so far as it is in harmony with our nature; and hence a thing is useful, in proportion as it is in harmony with our nature, and vice versa. Q.E.D.
Modern English
It follows that the more a thing agrees with our nature, the more useful, that is, the better, it is for us; and conversely, the more useful a thing is for us, the more it agrees with our nature. For in so far as a thing does not agree with our nature, it is necessarily either different from our nature or contrary to it. If different, it can be neither good nor bad (E4P29); if contrary, it is also contrary to what agrees with our nature, that is (E4P31), contrary to what is good, and therefore bad. Nothing, then, can be good except in so far as it agrees with our nature; and so a thing is useful in proportion as it agrees with our nature, and conversely.