§ 1. On Purchase and Sale in General

291. Definition. Purchase is defined in Roman law as "an agreement for a price in exchange for merchandise"; sale, however, as "an agreement for merchandise in exchange for a price."¹²⁵ Therefore purchase and sale are two correlative contracts constituting one whole, which is called "purchase-sale" and can be defined as: an onerous contract constituted by mutual consent for giving merchandise for a determinate price and the price for merchandise. Therefore, besides the mutual consent of buyer and seller, two elements are required for the contract of purchase and sale: a thing as merchandise, and a price, which is a sum of money to be paid for acquiring some thing. Money, which in civilized regions today is made of gold, silver, etc., in ancient times was constituted by many other things, e.g., cattle, skins, ivory, shells, etc. Money, therefore, is a medium established by universal agreement for effecting exchanges of ownership.¹²⁶ The mutual consent which in this contract transfers ownership both of the thing and of the price must sometimes, by civil laws, be expressed under a determinate form, e.g., before a notary. Otherwise the contract is considered null.

By natural law a sale is perfected as soon as the parties have agreed concerning the thing to be delivered and the price to be paid. But before the actual delivery of the thing, consent does not produce the same effects in different positive laws. In German¹²⁷ and Austrian¹²⁸ law, ownership of the thing is transferred to the buyer only by delivery; before delivery he has only a right to the thing and consequently a personal action against the seller. On the contrary, in French,¹²⁹ Spanish,¹³⁰ Italian,¹³¹ English, North American,¹³² and Swiss¹³³ law, ownership of the thing purchased, together with its risk and advantage, passes to the buyer by the consent of the parties alone. There are, however, exceptions which can be seen in the places cited.

For the sake of clarity we shall now treat separately: 1. the thing saleable, or the merchandise, and the obligation of the seller; 2. the price and the obligation of the buyer; and finally, in a proper paragraph, certain sales in particular.

¹²⁵ From L. 5, § 1, D. 19, 5.

¹²⁶ After Aristotle, the Angelic Doctor (lect. 9 on book 5 of the Ethics) explains excellently how money, and indeed coin, is not only a suitable medium for effecting exchanges of ownership, but also a measure of the value of individual things.

¹²⁷ Civil Code § 446.

¹²⁸ Civil Code § 1053.

¹²⁹ Civil Code art. 1583.

¹³⁰ Civil Code arts. 1452, 1468.

¹³¹ Civil Code art. 1448.

¹³² Cf. Tanquerey, Suppl., p. 21ff.

¹³³ Code of Obligations art. 185.