As pointed out in chapter 3, how and how strongly entitlements are protected – either as inalienable or by a property rule or a liability rule – must be distinguished from what the system does in case the rules of protection are not respected, that is, when faced with extra-contractual behavior (back-up enforcement). Earlier, I referred to this distinction as one between second- and third-order questions. I also pointed out that whilst in domestic law back-up enforcement is a given (there are police, bailiffs and prisons) in international law (which generally lacks central enforcement) the third-order question of back-up enforcement becomes a crucial part of the equation. As a result, even though this book focuses on the second-order question of how international law ought to protect entitlements, as noted earlier, any such inquiry must be made in the context of the third step of back-up enforcement.

Logically, one would expect that higher levels of protection will also be backed up with higher or stronger remedies in case that level is not met. Put differently, the more ambitious the goal, the more forceful the instruments to achieve that goal. This is exactly what we see in domestic law. Where entitlements are (highly) protected as inalienable (such as in criminal law) back-up enforcement takes the form of imprisonment, sometimes even the death penalty. The next level of protection by property rule is, in turn, backed up with court injunctions and fines, coupled, if necessary, with imprisonment.