The general law, then, respecting just or economical exchange, is simply this:--There must be advantage on both sides (or if only advantage on one, at least no disadvantage on the other) to the persons exchanging; and just payment for his time, intelligence, and labour, to any intermediate person effecting the transaction (commonly called a merchant): and whatever advantage there is on either side, and whatever pay is given to the intermediate person, should be thoroughly known to all concerned. All attempt at concealment implies some practice of the opposite, or undivine science, founded on nescience. Whence another saying of the Jew merchant's--"As a nail between the stone joints, so doth sin stick fast between buying and selling." Which peculiar riveting of stone and timber, in men's dealing with each other, is again set forth in the house which was to be destroyed--timber and stones together--when Zechariah's roll (more probably "curved sword") flew over it: "the curse that goeth forth over all the earth upon every one that stealeth and holdeth himself guiltless," instantly followed by the vision of the Great Measure;--the measure "of the injustice of them in all the earth" ([Greek: autê hê adikia autôn en pasê tê gê]), with the weight of lead for its lid, and the woman, the spirit of wickedness, within it;--that is to say, Wickedness hidden by Dulness, and formalized, outwardly, into ponderously established cruelty. "It shall be set upon its own base in the land on Babel."[53]
[53] Zech. v. 11. See note on the passage, at pp. 191-2.
I have hitherto carefully restricted myself, in speaking of exchange, to the use of the term "advantage;" but that term includes two ideas: the advantage, namely, of getting what we _need_, and that of getting what we _wish for_. Three-fourths of the demands existing in the world are romantic; founded on visions, idealisms, hopes, and affections; and the regulation of the purse is, in its essence, regulation of the imagination and the heart. Hence, the right discussion of the nature of price is a very high metaphysical and psychical problem; sometimes to be solved only in a passionate manner, as by David in his counting the price of the water of the well by the gate of Bethlehem; but its first conditions are the following:--The price of anything is the quantity of labour given by the person desiring it, in order to obtain possession of it. This price depends on four variable quantities. _A_. The quantity of wish the purchaser has for the thing; opposed to [Greek: a], the quantity of wish the seller has to keep it. _B_. The quantity of labour the purchaser can afford, to obtain the thing; opposed to [Greek: b], the quantity of labour the seller can afford, to keep it. These quantities are operative only in excess; _i.e._, the quantity of wish (_A_) means the quantity of wish for this thing, above wish for other things; and the quantity of work (_B_) means the quantity which can be spared to get this thing from the quantity needed to get other things.