I think the Hobbesian would say that the captor would not even enter into the contract if there was fear of your non-compliance. If you note later in paragraph 27 he adds the caveat "if trusted with the payment of their ransom" to the prisoner of war, I think it can be argued that this is his response to your concern about it being a valid contract. Basically for it to be valid both parties cannot have a reasonable suspicion of non-compliance. If the captor let's you go, obviously you know he's complying with the bargain. Now the captor cannot gaurantee compliance at this point, but that is clearly different from having a suspicion of non-compliance. If the captor has that suspicion it would be unreasonable to even make the bargain and so he/she would not, but if the captor did have that suspicion and still entered into the agreement, then I think it could be argued that the contract is void given paragraph 18. Though, I don't remember is Hobbes has any statements about irrational decisions, which is what this would seem to be. That help?
If Fontana can submit a plea for help, maybe I can, too. Does anyone have suggestions for a good essay on Derrida's Differance? I have to give a presentation on it next tuesday. I'm halfway through now, and have a lot of questions.
Wo'S: it might. The language suggests that such a trust is possible, which is a little bit mysterious. Also, this is made more tricky by the fact that these are prisoners of war, so the released prisoner & the erstwhile captor are not within a common political community, hence in 'a state of war' in the broad sense. It would be funny if covenants in a case like that rested on irrational decisions...
M: I'll post that plea.