4 Common stipulations may be exemplified by that by which a guardian gives security that his ward's property will not be squandered or misappropriated, which he is sometimes required to enter into by the praetor, and sometimes also by a judge when the matter cannot be managed in any other way; or, again, we might take the stipulation by which an agent promises that his acts shall be ratified by his principal.
TITLE XIX. OF INVALID STIPULATIONS
Anything, whether movable or immovable, which admits of private ownership, may be made the object of a stipulation; 1 but if a man stipulates for the delivery of a thing which either does not or cannot exist, such as Stichus, who is dead but whom he though alive, or an impossible creature, like a hippocentaur, the contract will be void.
2 Precisely the same principles applies where a man stipulates for the delivery of a thing which is sacred or religious, but which he thought was a subject of human ownership, or of a thing which is public, that is to say, devoted in perpetuity to the use and enjoyment of the people at large, like a forum or theatre, or of a free man whom he thought a slave, or of a thing which he is incapable of owning, or which is his own already. And the fact that a thing which is public may become private property, that a free man may become a slave, that the stipulator may become capable of owning such and such a thing, or that such and such a thing may cease to belong to him, will not avail to merely suspend the force of the stipulation in these cases, but it is void from the outset. Conversely, a stipulation which originally was perfectly good may be avoided by the thing, which is its object, acquiring any of the characters just specified through no fault of the promisor. And a stipulation, such as 'do you promise to convey Lucius Titius when he shall be a slave' and others like it, are also void from the beginning; for objects which by their very nature cannot be owned by man cannot either in any way be made the object of an obligation.
3 If one man promises that another shall convey, or do so and so, as, for instance, that Titius shall give five aurei, he will not be bound, though he will if he promises to get Titius to give them.
4 If a man stipulates for conveyance to, or performance in favour of, another person who is not his paterfamilias, the contract is void; though of course performance to a third person may be bargained for (as in the stipulation 'do you promise to give to me or to Seius?'); where, though the obligation is created in favour of the stipulator only, payment may still be lawfully made to Seius, even against the stipulator's will, the result of which, if it is done, being that the promisor is entirely released from his obligation, while the stipulator can sue Seius by the action of agency. If a man stipulates for payment of ten aurei to himself and another who is not his paterfamilias, the contract will be good, though there has been much doubt whether in such a case the stipulator can sue for the whole sum agreed upon, or only half; the law is now settled in favour of the smaller sum. If you stipulate for performance in favour of one in your power, all benefit under the contract is taken by yourself, for your words are as the words of your son, as his words are as yours, in all cases in which he is merely an instrument of acquisition for you.
5 Another circumstance by which a stipulation may be avoided is want of correspondence between question and answer, as where a man stipulates from you for payment of ten aurei, and you promise five, or vice versa; or where his question is unconditional, your answer conditional, or vice versa, provided only that in this latter case the difference is express and clear; that is to say, if he stipulates for payment on fulfilment of a condition, or on some determinate future day, and you answer: 'I. promise to pay today,' the contract is void; but if you merely answer: 'I promise,' you are held by this laconic reply to have undertaken payment on the day, or subject to the condition specified; for it is not essential that every word used by the stipulator should be repeated in the answer of the promise.
6 Again, no valid stipulation can be made between two persons of whom one is in the power of the other. A slave indeed cannot be under an obligation to either his master or anybody else: but children in power can be bound in favour of any one except their own paterfamilias.
7 The dumb, of course, cannot either stipulate or promise, nor can the deaf, for the promisee in stipulation must hear the answer, and the promisor must hear the question; and this makes it clear that we are speaking of persons only who are stone deaf, not of those who (as it is said) are hard of hearing.