Fifthly: The values of commodities are often said to be determined by the costs of production. When the costs of production do not refer to money, but to those simple elements of production, without an adequate quantity of which, whatever may be their price in money, the commodity cannot be produced, they are precisely the same as the natural and necessary conditions of the supply. The elementary costs of production, excluding rents and taxes, are the labour and profits required to produce a commodity. Of these it has been already shown, that the labour which the commodity will ordinarily command is alone the measure; and allowing that we could obtain with tolerable exactness the average price of common agricultural labour at different times and in different countries, and that when the prices of all other sorts of labour were once established, they would (as assumed by Adam Smith and Mr. Ricardo) continue to bear nearly the same relation to each other in the further progress of cultivation and improvement, it is certain that the quantity of common agricultural labour which a commodity would ordinarily command at any place and time would measure, with a near approach to accuracy, the elementary costs of production at that place and time; so that commodities, which at two different periods in the same country would ordinarily command the same quantity of agricultural labour, might fairly be said to be equal to each other in their elementary costs of production, and, of course, in their values, if their values be determined by their elementary costs of production.