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 the 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 per cent. 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. As it is the nominal or money price of goods, therefore, which finally determines the prudence or imprudence of all purchases and sales, and thereby regulates almost the whole business of common life in which price is concerned, we cannot wonder that it should have been so much more attended to than the real price. In such a work as this, however, it may sometimes be of use to compare the different real values of a particular commodity at different times and places, or the different degrees of power over the labour of other people which it may, upon different occasions, have given to those who possessed it. We must in this case compare, not so much the different quantities of silver for which it was commonly sold, as the different quantities of labour which those different quantities of silver could have purchased. But the current prices of labour, at distant times and places, can scarce ever be known with any degree of exactness. Those of corn, though they have in few places been regularly recorded, are in general better known, and have been more frequently taken notice of by historians and other writers. We must generally, therefore, content ourselves with them, not as being always exactly in the same proportion as the current prices of labour, but as being the nearest approximation which can commonly be had to that proportion. I shall hereafter have occasion to make several comparisons of this kind.