E4P71D
Demonstration — Part IV
Latin
Soli homines liberi sibi invicem utilissimi sunt et maxima amicitiæ necessitudine invicem junguntur (per propositionem 35 hujus et I ejus corollarium) parique amoris studio sibi invicem benefacere conantur (per propositionem 37 hujus) adeoque (per 34 affectuum definitionem) soli homines liberi erga se invicem gratissimi sunt. Q.E.D.
English (Elwes 1883)
Only free men are thoroughly useful one to another, and associated among themselves by the closest necessity of friendship (IV. xxxv., and Coroll. i.), only such men endeavour, with mutual zeal of love, to confer benefits on each other (IV. xxxvii.), and, therefore, only they are thoroughly grateful one to another. Q.E.D.