XXI. Hence may be solved the question to be found in Gellius, respecting a commission, whether it can be fulfilled by doing, not the immediate act required, but some thing equivalent to it, or in a manner more beneficial than in the form prescribed. For this deviation from the written rule may be proper and lawful, where the prescribed form is not essential towards attaining the object, or where, by departing from it, that object can be better accomplished, according to the answer given by Scaevola, that the person required to be bail and security for another, may give an order to a third person to pay that money to the creditor. But where such a latitude of interpretation is not evidently admissible, we must adhere to what Gellius has said in the same place, that it would be a dissolution of all trusts, if the party acting in commission were, in all cases, left to his own discretion, rather than bound by his written instructions. XXII. An interpretation, restricted more closely than the literal signification of the words containing a promise absolutely requires, may arise either from some original defect in the intention of the promiser, or from some subsequent emergency repugnant to such intention. Thus if it were evident that an absurdity would follow the fulfilment of a promise, this would be sufficient to prove an original defect in the intention, because no man can be supposed to have deliberately intended doing an absurd act. Or if the sole and effectual reason, by which the promise was influenced, should have ceased, the obligation also would be void, the sole ground on which it rested being no longer in existence. XXIII. In the next place, where any sufficient reason can evidently be assigned for a promise or engagement, it is not the substance of the promise itself, which is to be considered, so much as the reason for which that promise was given. XXIV. Thirdly, the contending parties must always be supposed to have in contemplation the subject, and nothing but the subject, however extensive a signification the words may seem to bear. This method of interpretation also is handled by the ancient rhetorical writers, in speaking of expression and design, and they place it under the head of VARIATIONS IN OPINION.