Page:Principles of Political Economy Vol 1.djvu/570

548 cost. To this class, as has been often repeated, agricultural produce belongs; and generally all the rude produce of the earth; and this peculiarity is a source of very important consequences; one of which is the necessity of a limit to population; and another, the payment of rent.

§ 3.These being the three classes, in one or other of which all things that are bought and sold must take their place, we shall consider them in their order. And first, of things absolutely limited in quantity, such as ancient sculptures or pictures.

Of such things it is commonly said, that their value depends upon their scarcity: but the expression is not sufficiently definite to serve our purpose. Others say, with somewhat greater precision, that the value depends on the demand and the supply. But even this statement requires much explanation, to make it a clear exponent of the relation between the value of a thing, and the causes of which that value is an effect.

The supply of a commodity is an intelligible expression: it means the quantity offered for sale; the quantity that is to be had, at a given time and place, by those who wish to purchase it. But what is meant by the demand? Not the mere desire for the commodity. A beggar may desire a diamond; but his desire, however great, will have no influence on the price. Writers have therefore given a more limited sense to demand, and have defined it, the wish to possess, combined with the power of purchasing. To distinguish demand in this technical sense, from the demand which is synonymous with desire, they call the former effectual demand. After this explanation, it is usually supposed that