§ I. DIFFERENTIAL ADVANTAGES IN CONSUMPTION GOODS [Sidenote: Connection between gratification, rents, and value of wealth] 1. _Both rent and the value of durable wealth are based on the value of the fruits or products yielded by the wealth._ Gratification, afforded directly or indirectly, is the basis of all values. The relation of most kinds of wealth to wants is indirect; but gratification thus afforded indirectly is none the less the basis on which the usufruct of wealth is estimated. Men find the logical or causal connection between direct goods, or final product, and indirect goods, or agents. To explain the value of the durable wealth, or rent-bearer, a still farther step in thought must be taken. The value of the rent-bearer is based on the series of rents which it affords. To explain how these rents are added to give the value of the indirect agents is the task of a theory of capitalization. This being the relation, a change in the value of the product changes the rent, and this in turn changes the value of the rent-bearer. The theory of rent, therefore, has to begin with a review of the valuation of enjoyable goods. [Sidenote: Effect of scarcity on utility of uniform goods] 2. _In a group of consumption goods, all of the same quality, the marginal utility declines as the quantity increases._ If the quantity of an article capable of ministering to man's wants is very limited, its value is high. If the supply of something of uniform quality, for which there is no substitute, is scanty, the value is estimated without reference to any other grade. If a fishing tribe caught very few fish, but these were all equally good, and if no other food were to be had, fish would have a high ratio of exchange with every other kind of goods. If the quantity increases, the value of each unit of the whole supply falls, as the importance attributed to its parts declines. If an Indian hunting-party met with unusual success, the value of buffalo meat declined. If there is a remarkable potato crop, potatoes fall in value. [Sidenote: Relation of different grades of consumption goods]