Note to Ad Valorem from Unto This Last by John Ruskin

Perhaps it may be said, in farther support of Mr. Ricardo, that he meant, "when the utility is constant or given, the price varies as the quantity of labour." If he meant this, he should have said it; but, had he meant it, he could have hardly missed the necessary result, that utility would be one measure of price (which he expressly denies it to be); and that, to prove saleableness, he had to prove a given quantity of utility, as well as a given quantity of labour: to wit, in his own instance, that the deer and fish would each feed the same number of men, for the same number of days, with equal pleasure to their palates. The fact is, he did not know what he meant himself. The general idea which he had derived from commercial experience, without being able to analyse it, was, that when the demand is constant, the price varies as the quantity of labour required for production; or, — using the formula I gave in last paper— when y is constant, xy varies as x. But demand never is, nor can be, ultimately constant, if x varies distinctly; for, as price rises, consumers fall away; and as soon as there is a monopoly (and all scarcity is a form of monopoly; so that every commodity is affected occasionally by some colour of monopoly), y becomes the most influential condition of the price. Thus the price of a painting depends less on its merit than on the interest taken in it by the public; the price of singing less on the labour of the singer than the number of persons who desire to hear him; and the price of gold less on the scarcity which affects it in common with cerium or iridium, than on the sun-light colour and unalterable purity by which it attracts the admiration and answers the trust of mankind.

It must be kept in mind, however, that I use the word "demand" in a somewhat different sense from economists usually. They mean by it "the quantity of a thing sold". I mean by it "the force of the buyer's capable intention to buy". In good English, a person's "demand" signifies, not what he gets, but what he, asks for.

Economists also do not notice that objects are not valued by absolute bulk or weight, but by such bulk and weight as is necessary to bring them into use. They say, for instance, that water bears no price in the market. It is true that a cupful does not, but a lake does; just as a handful of dust does not, but an acre does. And were it possible to make even the possession of the cupful or handful permanent (i.e., to find a place for them), the earth and sea would be bought up by handfuls and cupfuls.