Article II. On Modes Prefixed to a Contract

794. • A mode is an added quality, for the most part not suspending the contract, but adding something for the burden or favor of one of the contracting parties.

Modal contracts are made chiefly: 1. to a day; 2. under a cause; 3. under a penalty; 4. under a demonstration; 5. under a disjunction.

You will resolve. - 1. The mode must be observed from justice, unless it is repugnant to the substance of the contract.

2. Its violation ordinarily, and unless otherwise agreed, does not invalidate the contract, because it is held as something merely accidental.

3. If the mode is base or impossible, it is held as not added; nor is the contract invalid unless the mode is repugnant to its nature, or unless the will of the contracting person was wholly restricted to it.

4. In a contract to a day, the obligation arises immediately, but the effect is suspended to the determined day.

5. In a contract under a cause (because), or under a demonstration (I sell this or so much), error does not invalidate unless it pertains to the essence of the thing.

6. If the error is in quantity, the whole thing is owed if the quantity was designated demonstratively; but if taxatively, as they say, the excess of quantity is not owed. Moreover, the thing is judged designated demonstratively if the thing is expressed in the first place, and afterwards its quantity; e.g. I bequeath to Titius my farm of thirty acres; but taxatively if in the first place the quantity is expressed, and then the thing; e.g. I bequeath three gold coins in such a box. But the circumstances of the things must be weighed.

7. In a contract under a penalty, that is, whenever a penalty is imposed on one withdrawing, this penalty is owed from justice if it is requested, at least if the contract has not been fulfilled culpably. Nevertheless the penalty must be moderate; otherwise it would not oblige.

8. In a contract under a disjunction, e.g. I promise an ox or a horse, no determined thing is owed, and the payment of one removes the whole obligation. The choice of the thing of itself belongs to the debtor.