Full Idea
If one borrowed a weapon from a friend who subsequently went out of his mind and then asked for it back, surely one ought not to return it?
Gist of Idea
Surely you don't return a borrowed weapon to a mad friend?
Source
Plato (The Republic [c.371 BCE], 331c)
Book Reference
Plato: 'Republic', ed/tr. Waterfield,Robin [OUP 1993], p.8
A Reaction
Only a Kantian would think of disagreeing with this obvious truth. There is no promise here, but an implicit moral commitment. Such things should always have an all-things-being-equal clause.
Related Idea
Idea 8015 Hobbes wants a contract to found morality, but shared values are needed to make a contract [MacIntyre on Hobbes]