1. On keeping promises:

Machiavelli, Prince, chapter 18:

Title: “The Way Princes Should Keep Their Word”

“Thus a prudent prince cannot and should not keep his word when to do so would go against his interest, or when the reasons that made him pledge it no longer apply. Doubtless if all men were good, this rule would be bad; but since they are a sad lot, and keep no faith with you, you in your turn are under no obligation to keep it with them.”

“To preserve the state, he often has to do things against his word, against charity, against humanity, against religion. Thus he has to have a mind ready to shift as the winds of fortune and the varying circumstances of life may dictate.”

Hobbes, Leviathan, chapter 13:

“Hereby it is manifest that, during the time men live without a common power to keep them all in awe, they are in that condition which is called war, and such a war as is of every man against every man.”

“In such condition [of war] . . . the life of man is solitary, poor, nasty, brutish, and short.”

“To this war of every man against every man, this also is consequent: that nothing can be unjust.”

Leviathan, chapter 14:

“Words alone, if they be of the time to come and contain a bare promise, are an insufficient sign of a free gift and therefore not obligatory.”

If a covenant be made wherein neither of the parties perform presently but trust one another, in the condition of mere nature, which is a condition of way of every man against every man, upon any reasonable suspicion, it is void; but if there be a common power set over them both, with right and force sufficient to compel performance, it is not void. For he that performs first has no assurance the other wioll perform after.”

“[T]o perform his part [of a contract] at some determinate time after [the first party performs] and in the meantime be trusted . . ., the contract on his part is called PACT or COVENANT.”