Dr Smith was evidently led into this train of argument, from his habit of considering labour as the standard measure of value, and corn as the measure of labour. But, that corn is a very inaccurate measure of labour, the history of our own country will amply demonstrate; where labour, compared with corn, will be found to have experienced very great and striking variations, not only from year to year, but from century to century; and for ten, twenty, and thirty years together;(1*) and that neither labour nor any other commodity can be an accurate measure of real value in exchange, is now considered as one of the most incontrovertible doctrines of political economy, and indeed follows, as a necessary consequence, from the very definition of value in exchange. But to allow that corn regulates the prices of all commodities, is at once to erect it into a standard measure of real value in exchange; and we must either deny the truth of Dr Smith's argument, or acknowledge, that what seems to be quite impossible is found to exist; and that a given quantity of corn, notwithstanding the fluctuations to which its supply and demand must be subject, and the fluctuations to which the supply and demand of all the other commodities with which it is compared must also be subject, will, on the average of a few years, at all times and in all countries, purchase the same quantity of labour and of the necessaries and conveniences of life. There are two obvious truths in political economy, which have not infrequently been the sources of error. It is undoubtedly true, that corn might be just as successfully cultivated, and as much capital might be laid out upon the land, at the price of twenty shillings a quarter, as at the price of one hundred shillings, provided that every commodity, both at home and abroad, were precisely proportioned to the reduced scale. In the same manner as it is strictly true, that the industry and capital of a nation would be exactly the same (with the slight exception at least of plate), if, in every exchange, both at home or abroad, one shilling only were used, where five are used now.