III. In all acts of exchange, there is either an adjustment of shares, or the profits are regarded as a common stock. And such adjustments are made by the Roman Lawyers in the following terms, "I give this to receive that in return, I do this in order for you to do that, or I do this for you to give me that."[29] But the Romans exclude from that adjustment certain kinds of contracts, which they call EXPRESS ENGAGEMENTS. Not because they are entitled to any such peculiar name more than the simple acts of exchange already mentioned: but because from frequent use they have naturally derived a character similar to that of the original contract, from which they are named, though they are not attended exactly with the same circumstances, nor expressed directly in the same terms. Whereas in other contracts less frequently in use, the form was confined to an exact statement of all the circumstances of the case. An action upon which was therefore called by the Roman law an ACTION IN PRESCRIBED WORDS. For the same reason, if those contracts, which are in general use, be accompanied with any of the requisite formalities, as in a bargain or sale, if the price had been agreed upon, though no part of the agreement had been performed by either of the parties, the civil law enforced an obligation to fulfil them. But as it considers those contracts which are seldom used, more in the light of voluntary engagements, depending upon the good faith of the respective parties, than upon legal obligation, it leaves both sides at liberty to relinquish them at any time prior to their being naturally performed. Distinctions of this kind are unknown to the law of nature, which gives SIMPLE AGREEMENTS equal authority with those, that are included by civilians in the class of EXPRESS CONTRACTS. And on the score of antiquity their pretensions are far superior. It is therefore perfectly conformable to the principles of nature to reduce the adjustment of all agreements, without any regard to the distinction between SIMPLE and EXPRESS CONTRACTS, to the three species already named. Thus, for instance, one thing is given for another, which constitutes barter, the most ancient kind of traffic; the next step in the progress of commercial intercourse is where one kind of money is given for another, a transaction which by merchants is called exchange; and a third species of contract is where money is given for any thing, as in the acts of selling and buying. Or the USE of one thing may be given for that of another; money also may be given for the USE of a thing, which last method constitutes the acts of letting and hiring.