Page:Observations on the effects of the corn laws - Malthus -1814.djvu/20

 thirty years together : 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 unfrequently been the sources of error.