But though in establishing perpetual rents, or even in letting very long leases, it may be of use to distinguish between real and nominal price; it is of none in buying and selling, the more common and ordinary transactions of human life.
At the same time and place the real and the nominal price of all commodities are exactly in proportion to one another. The more or less money you get for any commodity, in the London market, for example, the more or less labour it will at that time and place enable you to purchase or command. At the same time and place, therefore, money is the exact measure of the real exchangeable value of all commodities. It is so, however, at the same time and place only.
Though at distant places, there is no regular proportion between the real and the money price of commodities, yet the merchant who carries goods from the one to the other has nothing to consider but their money price, or the difference between the quantity of silver for which he buys them, and that for which he is likely to sell them. Half an ounce of silver at Canton in China may command a greater quantity both of labour and of the necessaries and conveniencies of life, than an ounce at London. A commodity, therefore, which sells for half an ounce of silver at Canton may there be really dearer, of more real importance to the man who possesses it there, than a commodity which sells for an ounce at London is to the man who possesses it at London. If a London merchant, however, can buy at Canton for half an ounce of silver, a commodity which he can afterwards sell at London for an ounce, he gains a hundred percent by the bargain, just as much as if an ounce of silver was at London exactly of the same value as at Canton. It is of no importance to him that half an ounce of silver at Canton would have given him the command of more labour and of a greater quantity of the necessaries and conveniencies of life than an ounce can do at London. An ounce at London will always give him the command of double the quantity of all these, which half an ounce could have done there, and this is precisely what he wants.