Lex commissoria

Just as in the case of an in diem addictio, a standard form appears to have been used by the parties when they wished to add what was usually referred to as a lex commissoria^[3773] to their sale: "si ad diem pecunia soluta non sit, ut fundus inemptus sit", they would tend to say or write.^[3774] What this clause was designed to achieve is rather obvious: the vendor was to be given the right to call off the sale if the purchase price had not been paid by a certain time.^[3775] But for the lex commissoria he could avail himself of the actio venditi against the purchaser only to claim the price or damages; a unilateral right of withdrawal on account of mora or any other form of breach of contract did not exist in Roman law.^[3776] Unlike an in diem addictio, a lex commissoria was thus solely in the vendor's interest and it was, as a rule, taken to have a resolutive rather than a suspensive effect;^[3777] after all, the lex commissoria aimed at inducing the purchaser to render payment timeously and the parties could thus normally be taken to have presupposed that the obligation to pay had in fact become effective. In order to make the whole arrangement workable, the jurists determined that the sale did not collapse, ipso iure, if by the due date the purchase price had not been paid; for that would, effectively, have allowed the purchaser to call off the sale if he no longer wanted to be bound by it.

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