E4P72D
Demonstration — Part IV
Latin
Si liber homo quicquam dolo malo quatenus liber est, ageret, id ex dictamine rationis ageret (nam eatenus tantum liber a nobis appellatur) atque adeo dolo malo agere virtus esset (per propositionem 24 hujus) et consequenter (per eandem propositionem) unicuique ad suum esse conservandum consultius esset dolo malo agere hoc est (ut per se notum) hominibus consultius esset verbis solummodo convenire, re autem invicem esse contrarios, quod (per corollarium propositionis 31 hujus) est absurdum. Ergo homo liber etc. Q.E.D.
English (Elwes 1883)
If it be asked: What should a man's conduct be in a case where he could by breaking faith free himself from the danger of present death? Would not his plan of self--preservation completely persuade him to deceive? This may be answered by pointing out that, if reason persuaded him to act thus, it would persuade all men to act in a similar manner, in which case reason would persuade men not to agree in good faith to unite their forces, or to have laws in common, that is, not to have any general laws, which is absurd.
Modern English
If a free man were to act deceptively in any way insofar as he is free, he would be acting by the dictates of reason (for that is the only condition under which we call him free), and so acting deceptively would be a virtue (E4P24), and consequently (E4P24) it would be more advisable for everyone to act deceptively to preserve their being, that is, (as is self-evident), it would be more advisable for people to agree in words alone while actually being opposed to one another, which (by the Corollary to P31 of this Part (E4P31C)) is absurd. Therefore a free man, etc. Q.E.D.