Celsus, Digest, Book VI. If I stipulate for ten aurei from Titius, and I afterwards stipulate from Seius for the amount of the debt which I may fail to collect from Titius, then, if I bring suit against Titius for ten aurei, Seius will not be released from liability, otherwise the security provided by Seius will be worthless; but if Titius complies with the judgment, Seius will be no longer liable. If, however, I proceed against Seius, whatever the amount I can collect from Titius, when issue is joined between Seius and myself, is less than the obligation, so much the less can I subsequently collect from Titius. 1Labeo says that if you stipulate that a party shall see that ten aurei are paid, you cannot, for this reason, claim that ten should be paid to you, because the promisor can be released by finding a wealthier debtor; and, in fact, this means that the party cannot be compelled to join issue if he offers to provide a wealthier debtor.

Ad Dig. 12,6,47ROHGE, Bd. 22 (1878), Nr. 66, S. 299: Cond. possessionis gegen den aus Irrthum Besitzenden. Besitz ein Vermögensobject.Celsus, Digest, Book VI. You promised, through a mistake, to pay money which was not due, and the party who was your surety paid it. I am of the opinion that, if the surety paid it in your name you will then be liable to the surety, and the stipulator will be liable to you; for it is not to be expected that you should first ratify his act, since you may be held to have directed the surety to make payment in your name. If, however, the surety made payment in his own name of a sum which he did not owe, he can bring an action against the stipulator as having paid money which was not due under the Law of Nations; but where there is a deficiency in the amount which he can recover from the party whom he paid, this he can recover from you by an action on mandate; provided he who was bringing suit in ignorance of the facts should not be barred by an exception.

The Same, Digest, Book VI. Where anyone promises that, if something is done by him or when it has been done, he will pay ten aurei, and he pays the sum that he promised before the act is performed; he will not be held to have done what he promised, and therefore he can bring an action to recover the money.

Celsus, Digest, Book VI. Labeo says that the definition of peculium which Tubero gave does not include the peculium of sub-slaves, but this is not correct, for, by the very act that a master has granted peculium to his slave it must be understood that he has also granted it to the sub-slave.

Celsus, Digest, Book VI. When a question is raised with reference to the Lex Falcidia, the heir must prove that this law is applicable, because if he cannot do so, judgment will properly be rendered against him.

Celsus, Digest, Book VI. Where anyone charges his two appointed heirs as follows: “Let my heirs either deliver Stichus or ten aurei,” one of the heirs cannot tender five aurei to the legatee, and the other tender him half of Stichus, for it is necessary for Stichus to be entirely given, or the ten aurei to be paid.

Celsus, Digest, Book VI. Where anyone stipulated for ten aurei to be paid by one person and security to be given by another, the amount of damages should be estimated in proportion to the interest of the stipulator in having security furnished him. This interest can amount to as much as what is due, or to less, or sometimes even to nothing; for no estimate can be made of groundless fear. If, however, the debt should be paid, there will be no remaining interest to be estimated, and if a certain amount of it has been paid, the value of the interest will decrease in proportion. 1When anyone promises that he will prevent the stipulator from sustaining any loss, and he does so, and the stipulator does not suffer any damage, he is considered to have done what he agreed to. If he fails to do this, judgment will be rendered against him for a certain sum of money, for the reason that he did not do what he promised, as happens in all kinds of obligations which relate to the performance of certain acts.