Sometimes an exception, which prima facie seems just to the defendant, is unjust to the plaintiff, in which case the latter must protect himself by another allegation called a replication, because it parries and counteracts the force of the exception. For example, a creditor may have agreed with his debtor not to sue him for money due, and then have subsequently agreed with him that he shall be at liberty to do so; here if the creditor sues, and the debtor pleads that he ought not to be condemned on proof being given of the agreement not to sue, he bars the creditor's claim, for the plea is true, and remains so in spite of the subsequent agreement; but as it would be unjust that the creditor should be prevented from recovering, he will be allowed to plead a replication, based upon that agreement.

1 Sometimes again a replication, though prima facie just, is unjust to the defendant; in which case he must protect himself by another allegation called a rejoinder:

2 and if this again, though on the face of it just, is for some reason unjust to the plaintiff, a still further allegation is necessary for his protection, which is called a surrejoinder.

3 And sometimes even further additions are required by the multiplicity of circumstances under which dispositions are made, or by which they are subsequently affected; as to which fuller information may easily be gathered from the larger work of the Digest.

4 Exceptions which are open to a defendant are usually open to his surety as well, as indeed is only fair: for when a surety is sued the principal debtor may be regarded as the real defendant, because he can be compelled by the action on agency to repay the surety whatsoever he has disbursed on his account. Accordingly, if the creditor agrees with his debtor not to sue, the latter's sureties may plead this agreement, if sued themselves, exactly as if the agreement had been made with them instead of with the principal debtor. There are, however, some exceptions which, though pleadable by a principal debtor, are not pleadable by his surety; for instance, if a man surrenders his property to his creditors as an insolvent, and one of them sues him for his debt in full, he can effectually protect himself by pleading the surrender; but this cannot be done by his surety, because the creditor's main object, in accepting a surety for his debtor, is to be able to have recourse to the surety for the satisfaction of his claim if the debtor himself becomes insolvent.