1. Certain things are essential in every sale of anything, and of course are common to all sales of everything, such as two persons and two desires and two estimates and two renderings; while there are certain _peculiarities_ in the sale of things belonging to each of the three special classes of things salable; for example, in the sale of a commodity there is a rendering of a tangible object that has been prepared for sale in past time, and in the sale of a service a rendering of an intangible something wholly in the present time; while in the sale of a credit there are likewise two peculiarities, one of them relating to future time and the other to a special trust felt in a person by some other person. We must now study these two peculiarities with care; and, mastering these, we shall be master of the Nature of Credit. a. Some sales are consummated at once, the things exchanged and the ownership in them are mutually passed over then and there, the reciprocal satisfactions are entered upon immediately, and there is at once an economical end. For example, one neighbor sells another a peck of green peas and takes in pay a peck of new potatoes, both vegetables may be cooked for dinner in the respective families the same day, and the commercial transaction is all over. But there are other exchanges, an immense class of them, different from these in this respect, that though the transaction considered as a mere case of value created and measured is then and there ended, yet considered as to the nature of that preliminary exchange which implies and requires another future exchange to consummate it, it is not then and there ultimately closed, but one (or both) of the parties then exchanging relies on the good faith of some one else to fulfil in the future a pledge expressly or impliedly made in the prior exchange. Commonly some external evidence of the pledge is created and passed at the time, but this is not essential to the validity of the pledge itself. For example, A buys 50 bushels of wheat of B, and B takes in pay for it A's note of hand at six months for $75. The note is not the pledge, but it is a legal and convenient proof of it. As a case in Value, the wheat is sold for the pledge and the pledge is the equivalent of the wheat. Each party rendered the other then and there satisfactory equivalents. All our definitions apply here perfectly.