Possessing utility, commodities derive their exchangeable value from two sources: from their scarcity, and from the quantity of labour required to obtain them. David Ricardo
On the whole it may be observed, that the specific use of a body of unproductive consumers, is to give encouragement to wealth by maintaining such a balance between produce and consumption as will give the greatest exchangeable value to the results of the national industry. Thomas Malthus
The exchangeable value of all commodities, rises as the difficulties of their production increase. David Ricardo
Labour, therefore, is the real measure of the exchangeable value of all commodities. Adam Smith
In stating the principles which regulate exchangeable value and price, we should carefully distinguish between those variations which belong to the commodity itself, and those which are occasioned by a variation in the medium in which value is estimated, or price expressed. David Ricardo