4 A sale may be made conditionally as well as absolutely. The following is an example of a conditional sale: 'If Stichus meets with your approval within a certain time, he shall be purchased by you for so many aurei.' 5 If a man buys a piece of land which is sacred, religious, or public, such as a forum or basilica, knowing it to be such, the purchase is void. But if the vendor has fraudulently induced him to believe that what he was buying was not sacred, or was private property, as he cannot legally have what he contracted for, he can bring the action on purchase to recover damages for what he has lost by the fraud; and the same rule applies to the purchase of a free man represented by the vendor to be a slave. TITLE XXIV. OF LETTING AND HIRING The contract of hire resembles very closely the contract of sale, and the same rules of law apply to both. Thus, as the contract of sale is concluded as soon as the price is agreed upon, so the contract of hire is held to be concluded as soon as the sum to be paid for the hiring is settled, and from that moment the letter has an action on the letting, and the hirer on the hiring. 1 What we have said above as to a sale in which the price is left to be fixed by a third person must be understood to apply also to a contract of hire in which the amount to be paid for hire is left to be fixed in the same way. Consequently, if a man gives clothes to a fuller to clean or finish, or to a tailor to mend, and the amount of hire is not fixed at the time, but left to subsequent agreement between the parties, a contract of hire cannot properly be said to have been concluded, but an action is given on the circumstances, as amounting to an innominate contract. 2 Again, a question often arose in connexion with the contract of hire similar to that which was so common, namely, whether an exchange was a sale. For instance, what is the nature of the transaction if a man gives you the use or enjoyment of a thing, and receives in return the use or enjoyment of another thing from you? It is now settled that this is not a contract of hire, but a kind of contract apart by itself. Thus, if a man had one ox, and his neighbour another, and they agreed that each should in turn lend the other his ox for ten days to make use of, and then one of the oxen died while working for the man to whom it did not belong, an action cannot be brought on hire, nor on a loan for use, for a loan for use ought to be gratuitous: but an action should be brought as on an innominate contract.