[jaclaz]

The idea was that if you (British) had a (American) prisoner, you would release him in exchange for another (British) prisoner and - viceversa - if you (American) had a (British) prisoner you would release it in exchnage for a (American) prisoner.

A simple exchange.

The Americans had not the means (jails/prisons) to keep the prisoners in, so (evidently initially agreed with the British or anyway a comnmon at the time rule of honour in war times) they had the prisoner sign this "parole" document which amounted to an admission that the person had been captured in an action of war and that he was "virtually" a prisoner of the opposite army, even if actually set free, all in all not much different from a "I owe you ..." paper.

So, in theory, one parole=one prisoner, and periodically the British and the American would settle the balance by releasing prisoners (in exchange for a same amount of prisoners or paroles).

That until the British (to the utter Benjamin Franklin incredulity/astonishment) decided unilaterally that the "parole" was nothing but a piece of paper.

In the letter Franklin says that he has 500 paroles (up to then "worth" 500 prisoners) that suddenly were worth nothing.

[User23]

That's amusing. It's analogous to the difference between paper money and specie at the time.