Ad Dig. 5,1,35ROHGE, Bd. 9 (1873), S. 33: Zulässigkeit der Klagen auf Feststellung eines obligatorischen Verhältnisses.The Same, Epistles, Book X. It is not true that, as the obligation of a surety can be left dependent upon circumstances or contracted for at some future time, so also a suit may be contingent, or in such terms that an obligation may be subsequently incurred; for I do not think that anyone would doubt that a surety can be accepted before the obligation of the principal debtor is incurred, but issue cannot be joined before some indebtedness arises.

The Same, Epistles, Book X. I stipulated with Titius as follows, “If some woman marries me, do you promise to give me ten aurei by way of dowry?” The question arose whether such a stipulation was valid. The answer was that if the dowry was promised to me, stipulating as follows: “Do you promise to pay me ten aurei by way of dowry, no matter what woman I marry?” there is no reason why the money should not be due, if the condition was complied with. For when a condition dependent upon the act of some person who is uncertain can create an obligation, as, for instance, “Do you promise to pay ten aurei if anyone ascends to the Capitol?” or, “If anyone demands ten aurei of me, do you promise to pay as many?” there is no reason why the same answer should not be given as in the case where a dowry was promised. 1Ad Dig. 45,1,108,1ROHGE, Bd. 16 (1875), Nr. 109, S. 427, 429: Ergänzung unbestimmt gelassener Vereinbarungen. Arbitrium boni viri.No promise is valid which depends upon the will of the person who makes it.

Javolenus, Epistles, Book X. If I accept a surety under the following terms, “Do you agree to be responsible for the delivery of a thousand measures of wheat, to be paid for with your money, as security for the ten aurei which I have lent?” the surety will not be liable, because he cannot become responsible for something different from what has been lent, because the estimate of the value of the property which is considered as merchandise can be made in money; just as a sum of money can be estimated in merchandise.

The Same, Epistles, Book X. The money which you owe me, or any other property which I direct you to produce in my presence, when this is done, causes you immediately to be released, and the property to belong to me. For as the possession of the said property is not actually held by anyone, it is acquired by me, and is, as it were, considered to be delivered to me manu longa.

The Same, Epistles, Book X. Every provision contained in a will is not considered to have any effect, unless it was valid at the time it was made.