Article II. On Modes Prefixed to a Contract

A mode is an added quality, for the most part not suspending the contract, but adding something to the burden or favor of one of the contracting parties. Modal contracts are made chiefly: 1st, to a day; 2nd, under a cause; 3rd, under a penalty; 4th, under demonstration; 5th, under disjunction.

Concerning modes the following things are to be noted:

1st. A mode must be observed from justice, unless it is repugnant to the substance of the contract.

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

3rd. 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 party was altogether restricted to it.

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

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

6th. 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, a thing is judged designated demonstratively if the thing is expressed in the first place and afterwards its quantity, for example, I leave to Titius my estate of thirty acres; but taxatively, if the quantity is expressed in the first place, and then the thing; for example, I leave three gold coins in such a casket. But the adjuncts of things must be weighed.

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

8th. In a contract under disjunction, for example, I promise an ox or a horse, no determined thing is owed, and the payment of one takes away the whole obligation. Choice of the thing in itself pertains to the debtor.