[PAULUS libro duodecimo ad Sabinum. ] §45.1.35.prSi stipulor, ut id fiat, quod natura fieri non concedit, non magis obligatio consistit, quam cum stipulor ut detur quod dari non potest: nisi per quem stetit, quo minus facere id possit.
[PAUL, in the twelfth book on Sabinus.] If I stipulate that something be done which nature does not allow to be done, the obligation is no more established than when I stipulate that something be given which cannot be given: unless it was due to the person [the promisor] that he could not perform it.
§45.1.35.1Item quod leges fieri prohibent, si perpetuam causam seruaturum est, cessat obligatio, ueluti si sororem nupturam sibi aliquis stipuletur: quamquam etiamsi non sit perpetua causa, ut reccidit in sorore adoptiua, idem dicendum sit, quia statim contra mores sit.
Likewise, as to that which the laws forbid to be done, if it is to maintain a permanent impediment, the obligation is of no effect, as, for example, if someone should stipulate for his sister to marry him: although even if the impediment is not permanent, as occurs in the case of an adoptive sister, the same must be said, because it is immediately contrary to good morals.
§45.1.35.2Si in locando conducendo, uendendo emendo ad interrogationem quis non responderit, si tamen consentitur in id, quod responsum est, ualet quod actum est, quia hi contractus non tam uerbis quam consensu confirmantur.
If, in leasing and hiring, or selling and buying, anyone does not answer to a question, yet if there is consent to that which was answered, what was done is valid, because these contracts are established not so much by words as by consent.