The whole quantity of industry annually employed in order to bring any commodity to market, naturally suits itself in this manner to the effectual demand. It naturally aims at bringing always that precise quantity thither which may be sufficient to supply, and no more than supply, that demand.
But in some employments the same quantity of industry will in different years produce very different quantities of commodities; while in others it will produce always the same, or very nearly the same. The same number of labourers in husbandry will, in different years, produce very different quantities of corn, wine, oil, hops, etc. But the same number of spinners and weavers will every year produce the same or very nearly the same quantity of linen and woollen cloth. It is only the average produce of the one species of industry which can be suited in any respect to the effectual demand; and as its actual produce is frequently much greater and frequently much less than its average produce, the quantity of the commodities brought to market will sometimes exceed a good deal, and sometimes fall short a good deal, of the effectual demand. Even though that demand therefore should continue always the same, their market price will be liable to great fluctuations, will sometimes fall a good deal below, and sometimes rise a good deal above, their natural price. In the other species of industry, the produce of equal quantities of labour being always the same, or very nearly the same, it can be more exactly suited to the effectual demand. While that demand continues the same, therefore, the market price of the commodities is likely to do so too, and to be either altogether, or as nearly as can be judged of, the same with the natural price. That the price of linen and woollen cloth is liable neither to such frequent nor to such great variations as the price of corn, every man’s experience will inform him. The price of the one species of commodities varies only with the variations in the demand: That of the other varies not only with the variations in the demand, but with the much greater and more frequent variations in the quantity of what is brought to market in order to supply that demand.