Question One: On Purchase and Sale

511. Purchase-sale (achat et vente; koop en verkoop) is the type of an onerous contract. - Purchase is an agreement of price for merchandise; sale is an agreement of merchandise for price. They are two partial correlative contracts making one whole. Purchase-sale is defined as a bilateral onerous contract by which the dominion of some thing is transferred for a determined price, or a contract constituted by mutual consent for handing over merchandise into dominion for a determined price, and price for merchandise (a. 1582). It is called:

a bilateral contract, and thus is distinguished from donation;

onerous, that it may be distinguished from loan for consumption and loan for use;

by which dominion is transferred: thus it is distinguished both from a promise of sale, by which no dominion or right in the thing is transferred, and from letting-hiring, by which only use alone is transferred;

of some thing or merchandise, that it may be distinguished from exchange, by which money is given for other diverse money;

for a determined price: thus it is distinguished from barter, by which merchandise is exchanged with merchandise. But it is necessary that the price be determined: for if it is left to be determined by the buyer, the contract is null.

Therefore three conditions are required for the essence of this contract:

a) the mutual consent of one who buys and of another who sells, unto the transfer of dominion;

b) a thing determined as merchandise, that is, a thing estimable by price, whether movable or immovable; and thus sale is distinguished from exchange, in which one kind of money is exchanged for another kind of money, for instance French for English, silver for gold;

c) money determined as the determined price of the merchandise; and thus purchase is distinguished from simple barter, in which merchandise is given for merchandise, for example, a horse or ox for sheep.

Money, constituted by universal agreement, is the common measure of the value of things and thus a suitable means for comparing things with one another and exchanging them. Today it consists of coins or monies of gold, silver, etc., or of bank notes representing them; but in the first times it consisted of many other things, such as skins, ivory, shells, fish, cattle. Hence the name money (pecunia) is taken from cattle (pecus); and among certain nations coins were marked with the head of cattle.

512. Sale by its nature is a consensual contract, which is completed by the consent alone of the parties (a. 1583), so that the contract has force at once, before the thing has been handed over or the price paid. Therefore from the moment of mutual consent the dominion and risk of the thing are with the buyer; and the thing perishes for the buyer, unless it perishes by an intrinsic defect (a. 1647), or unless it happens from culpable delay of the seller because it was not handed over in due time (a. 1138-1141).

Exceptionally, however, sale is not completed by the consent of the parties:

a) if it is explicitly stipulated thus in the contract;

b) when things are not sold in bulk, but according to weight, number, and measure, for tasting or testing: then the contract will not be perfected until the things have been weighed, numbered, measured, tasted, and tested (a. 1585-1588);

c) if positive law so establishes generally: thus formerly Roman law; today, however, this obtains only in German and Austrian law. Then, namely, sale is not perfected until the thing has been handed over.

In these cases, as long as the sale has not been perfected, dominion of the thing and risk are with the seller, and the thing perishes for the seller.