Q.E.D.
Note .-- The goodwill, which men who are led by blind desire have for one another, is generally a bargaining or enticement, rather than pure goodwill.

Moreover, ingratitude is not an emotion.

Yet it is base, inasmuch as it generally shows, that a man is affected by excessive hatred, anger, pride, avarice, &c.
He who, by reason of his folly, knows not how to return benefits, is not ungrateful, much less he who is not gained over by the gifts of a courtesan to serve her lust, or by a thief to conceal his thefts, or by any similar persons.

Contrariwise, such an one shows a constant mind, inasmuch as he cannot by any gifts be corrupted, to his own or the general hurt.
PROP.LXXII.

The free man never acts fraudulently, but always in good faith.
Proof .-- 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.
PROP.LXXIII.