E4P35C2
Corollary — Part IV
Latin
Cum maxime unusquisque homo suum sibi utile quærit, tum maxime homines sunt sibi invicem utiles. Nam quo magis unusquisque suum utile quærit et se conservare conatur eo magis virtute præditus est (per propositionem 20 hujus) sive quod idem est (per definitionem 8 hujus) eo majore potentia præditus est ad agendum ex suæ naturæ legibus hoc est (per propositionem 3 partis III) ad vivendum ex ductu rationis. At homines tum maxime natura conveniunt cum ex ductu rationis vivunt (per propositionem præcedentem); ergo (per præcedens corollarium) tum maxime homines erunt sibi invicem utiles cum maxime unusquisque suum utile sibi quærit. Q.E.D.
English (Elwes 1883)
As every man seeks most that which is useful to him, so are men most useful one to another. For the more a man seeks what is useful to him and endeavours to preserve himself, the more is he endowed with virtue (IV. xx.), or, what is the same thing (IV. Def. viii.), the more is he endowed with power to act according to the laws of his own nature, that is to live in obedience to reason. But men are most in natural harmony, when they live in obedience to reason (by the last Prop.); therefore (by the foregoing Coroll.) men will be most useful one to another, when each seeks most that which is useful to him. Q.E.D.
Modern English
The more each person seeks what is useful for them, the more useful people are to one another. For the more a person seeks their own utility and strives to preserve themselves, the more virtue they possess (E4P20), or, what is the same thing (E4D8), the greater power they have to act according to the laws of their own nature, that is (E3P3), to live under the guidance of reason. But people are most in agreement with one another in nature when they live under the guidance of reason (E4P35). Therefore (E4P35C1) people are most useful to one another when each seeks most what is useful for themselves. Q.E.D.