18 When several acts of conveyance or performance are comprised in a single stipulation, if the promisor simply answers: 'I promise to convey,' he becomes liable on each and all of them, but if he answers that he will convey only one or some of them, he incurs an obligation in respect of those only which are comprised in his answer, there being in reality several distinct stipulations of which only one or some are considered to have acquired binding force: for for each act of conveyance or performance there ought to be a separate question and a separate answer. 19 As has been already observed, no one can validly stipulate for performance to a person other than himself, for the purpose of this kind of obligation is to enable persons to acquire for themselves that whereby they are profited, and a stipulator is not profited if the conveyance is made to a third person. Hence, if it be wished to make a stipulation in favour of any such third person, a penalty should be stipulated for, to be paid, in default of performance of that which is in reality the object of the contract, to the party who otherwise would have no interest in such performance; for when one stipulates for a penalty, it is not his interest in what is the real contract which is considered, but only the amount to be forfeited to him upon nonfulfilment of the condition. So that a stipulation for conveyance to Titius, but made by some one else, is void: but the addition of a penalty, in the form 'If you do not convey, do you promise to pay me so many aurei?' makes it good and actionable. 20 But where the promisor stipulates in favour of a third person, having himself an interest in the performance of the promise, the stipulation is good. For instance, if a guardian, after beginning to exercise his tutorial functions, retires from their exercise in favour of his fellow guardian, taking from him by stipulation security for the due charge of the ward's property, he has a sufficient interest in the performance of this promise, because the ward could have sued him in case of maladministration, and therefore the obligation is binding. So too a stipulation will be good by which one bargains for delivery to one's agent, or for payment to one's creditor, for in the latter case one may be so far interested in the payment that, if it not be made, one will become liable to a penalty or to having a foreclosure of estates which one has mortgaged. 21 Conversely, he who promises that another shall do so and so is not bound unless he promises a penalty in default; 22 and, again, a man cannot validly stipulate that property which will hereafter be his shall be conveyed to him as soon as it becomes his own. 23 If a stipulator and the promisor mean different things, there is no contractual obligation, but it is just as if no answer had been made to the question; for instance, if one stipulates from you for Stichus, and you think he means Pamphilus, whose name you believed to be Stichus.