d. Defences
1 The surety is entitled and obliged to plead against the creditor all defences open to the principal debtor or his heirs which are not based on the insolvency of the principal debtor. Suretyship for obligations that are not binding on the principal debtor owing to error or incapacity to make a contract or for time-barred obligations is reserved.
2 Where the principal debtor waives a defence that is open to him, the surety may nevertheless plead it.
3 Where the surety fails to plead defences open to the principal debtor, he forfeits his right of recourse to the extent that such defences would have released him from liability unless he can prove that he was unaware of them through no fault of his own.
4 A person who stands surety for an obligation that is not actionable because it stems from gambling or betting may plead the same defences as are open to the principal debtor even if he was aware of that defect.
b. Réduction légale de la garantie
1 Lorsque la caution est une personne physique, le montant total dont elle est tenue diminue chaque année, sauf dérogation convenue d’emblée ou subséquemment, de 3 %, et, si la créance est garantie par un gage immobilier, de 1 %. Dans tous les cas, le montant dont est tenue la personne physique diminue au moins dans la même proportion que la dette.
2 Font exception les cautionnements de dettes de droit public envers la Confédération ou ses établissements de droit public ou envers un canton, comme les droits de douane, les impôts et autres droits semblables, et les cautionnements de transport, ainsi que les cautionnements d’officiers publics et d’employés et les cautionnements de dettes à montant variable, comme les comptes courants et les contrats de vente par livraisons successives, et de prestations périodiques.