3.1.158 to 3.1.163

(138) An absent person can be charged in writing with the disbursement of money although a verbal obligation cannot be contracted with one who is absent. (139) Purchase and sale are contracted as soon as the price is agreed upon, although the price may not have been paid, [1] or any earnest money given; for what is given by way of earnest money is only a proof of the conclusion of a contract of purchase and a sale. (140) Moreover, the price must be certain; for, otherwise, if we agree that property shall be purchased for the amount at which Titius may estimate its value, Labeo denies that a transaction of this kind has any force or effect; and Cassius agrees with him. Ofilius holds that it is a purchase and sale, and Proculus adopts his opinion. (141 )Moreover, the price must consist of money, for it is seriously questioned whether it can consist of any other property, as for instance, a slave, a robe, or a tract of land. Our preceptors think that a price can consist of other property, and hence is derived the common opinion that purchase and sale are contracted by exchange of articles, and that this kind of purchase and sale is of the highest antiquity, and in proof of their contention, they adduce the statement of the Greek poet Homer, who somewhere says: "Here landed Achæan ships in search of wine. They purchased it with copper and with iron; With hides, with horned cattle, and with slaves." Authorities belonging to the other school dissent from this, and think that the exchange of articles is one thing, and purchase and sale another, as where property is exchanged it cannot be determined what is sold and what is given by way of price; and, on the other hand, it is absurd to consider that both articles are sold, and at the same time given by way of price. Cælius Sabinus says that if you have some property for sale, for example land, and I receive it, and give you a slave by way of price, the land should be considered to have been sold, and the slave given by way of price, as the land is what is received.