It is evident then, that the trade with a colony may be so regulated, that it shall at the same time be less beneficial to the colony, and more beneficial to the mother country, than a perfectly free trade. As it is disadvantageous to a single consumer to be restricted in his dealings to one particular shop, so is it disadvantageous for a nation of consumers to be obliged to purchase of one particular country. If the shop or the country afforded the goods required the cheapest, they would be secure of selling them without any such exclusive privilege; and if they did not sell cheaper, the general interest would require that they should not be encouraged to continue a trade which they could not carry on at an equal advantage with others. The shop, or the selling country, might lose by the change of employments, but the general benefit is never so fully secured, as by the most productive distribution of the general capital; that is to say, by an universally free trade.
An increase in the cost of production of a commodity, if it be an article of the first necessity, will not necessarily diminish its consumption; for although the general power of the purchasers to consume, is diminished by the rise of any one commodity, yet they may relinquish the consumption of some other commodity whose cost of production has not risen. In that case, the quantity supplied will be in the same proportion to the demand as before; the cost of production only will have increased, and yet the price will rise, and must rise, to place the profits of the producer of the enhanced commodity on a level with the profits derived from other trades.
M. Say acknowledges that the cost of production is the foundation of price, and yet in various parts of his book he maintains that price is regulated by the proportion which demand bears to supply. The real and ultimate regulator of the relative value of any two commodities, is the cost of their production, and neither the respective quantities which may be produced, nor the competition amongst the purchasers.