re bilateral, that is, both parties incur a reciprocal
obligation to perform whatever is just and fair, whereas verbal
contracts are unilateral, one party being promisee, and the other alone
promisor.

TITLE XXIII. OF PURCHASE AND SALE

The contract of purchase and sale is complete immediately the price
is agreed upon, and even before the price or as much as any earnest is
paid: for earnest is merely evidence of the completion of the contract.
In respect of sales unattested by any written evidence this is a
reasonable rule, and so far as they are concerned we have made no
innovations. By one of our constitutions, however, we have enacted, that
no sale effected by an agreement in writing shall be good or binding,
unless that agreement is written by the contracting parties themselves,
or, if written by some one else, is at least signed by them, or finally,
if written by a notary, is duly drawn by him and executed by the
parties. So long as any of these requirements is unsatisfied, there is
room to retract, and either purchaser or vendor may withdraw from the
agreement with impunity--provided, that is to say, that no earnest has
been given. Where earnest has been given, and either party refuses to
perform the contract, that party, whether the agreement be in writing or
not, if purchaser forfeits what he has given, and if vendor is compelled
to restore double of what he has received, even though there has been no
express agreement in the matter of earnest.

1 It is necessary that the price should be settled, for without a
price there can be no purchase and sale, and it ought to be a fixed and
certain price. For instance, where the parties agreed that the thing
should be sold at a price to be subsequently fixed by Titius, the older
jurists doubted much whether this was a valid contract of sale or not.
The doubt has been settled in the following way by our decision; if the
third person named actually fixes the price, it must certainly be paid,
as settled by him, and the thing must be delivered, in order to give
effect to the sale; the purchaser (if not fairly treated) suing by the
action on purchase, and the vendor by the action on sale. But if the
third person named will not or cannot fix the price, the sale will
be void, because no price has been settled. This rule, which we have
adopted with regard to sales, may reasonably be extended also to
contracts of hire.

2 The price, too, should be in money; for it used t