This is why we cannot refer to the debt as a legally enforceable obligation.

The concept of natural obligation is put forward as a means of allowing discharge of a "debt" which is legally unenforceable (either because of a procedural bar such as the Statute of Limitations or because the "debt" only exists as a moral obligation such as the obligation to provide for retired parents (to borrow an example from French Law)) to be good consideration.

The Statute of Limitations does not preclude any judicial finding that the debt ever was. It is much less sophisticated in its operation. It simply precludes recovery. It does not extinguish the indebtedness, it extinguishes the cause of action to enforce the indebtedness. Why else can one simply "affirm" one's indebtedness and thereby waive one's right to rely on the time bar? In what other areas of law can a simple affirmation of indebtedness suffice to create a binding obligation to pay?

Matthew Scully.
Oxford Institute of Legal Practice.