silver, by the richness or barrenness of the mines which supply the market with that metal, or by the quantity of labour which must be employed, and consequently of corn which must be consumed, in order to bring any particular quantity of silver from the mine to the market. But the value of silver, though it sometimes varies greatly from century to century, seldom varies much from year to year, but frequently continues the same, or very nearly the same, for half a century or a century together. The ordinary or average money price of corn, therefore, may, during so long a period, continue the same or very nearly the same too, and along with it the money price of labour, provided, at least, the society continues, in other respects, in the same or nearly in the same condition. In the meantime the temporary and occasional price of corn may frequently be double, one year, of what it had been the year before, or fluctuate, for example, from five and twenty to fifty shillings the quarter. But when corn is at the latter price, not only the nominal, but the real value of a corn rent will be double of what it is when at the former, or will command double the quantity either of labour or of the greater part of other commodities; the money price of labour, and along with it that of most other things, continuing the same during all these fluctuations.
Labour, therefore, it appears evidently, is the only universal, as well as the only accurate measure of value, or the only standard by which we can compare the values of different commodities at all times and at all places. We cannot estimate, it is allowed, the real value of different commodities from century to century by the quantities of silver which were given for them. We cannot estimate it from year to year by the quantities of corn. By the quantities of labour we can, with the greatest accuracy, estimate it both from century to century and from year to year. From century to century, corn is a better measure than silver, because, from century to century, equal quantities of corn will command the same quantity of labour more nearly than equal quantities of silver. From year to year, on the contrary, silver is a better measure than corn, because equal quantities of it will more nearly command the same quantity of labour.