4 Similarly, if at his creditor's challenge a debtor affirms on oath that he is not under an obligation to convey, he still remains bound; but as it would be unfair to examine whether he has perjured himself, he can, on being sued, set up the defence that he has sworn to the nonexistence of the debt. In real actions, too, exceptions are equally necessary; thus, if on the plaintiff's challenge the defendant swears that the property is his, there is nothing to prevent the former from persisting in his action; but it would be unfair to condemn the defendant, even though the plaintiff's contention that the property is his be well founded. 5 Again, an obligation still subsists even after judgement in an action, real or personal, in which you have been defendent, so that in strict law you may be sued again on the same ground of action; but you can effectually meet the claim by pleading the previous judgement. 6 These examples will have been sufficient to illustrate our meaning; the multitude and variety of the cases in which exceptions are necessary may be learnt by reference to the larger work of the Digest or Pandects. 7 Some exceptions derive their force from statutes or enactments equivalent to statutes, others from the jurisdiction of the praetor; 8 and some are said to be perpetual or peremptory, others to be temporary or dilatory. 9 Perpetual or peremptory exceptions are obstructions of unlimited duration, which practically destroy the plaintiff's ground of action, such as the exceptions of fraud, intimidation, and agreement never to sue.