There is an independent reason for the value of each grade of goods; each grade would have value if there were none of the other, but they mutually affect each other's value when they exist, side by side, in the same market. The marginal utility of each is lessened by the presence of the other. And thus, two or ten grades constitute for many purposes a single supply as they shade into each other or are merged by substitution.
Grades of Consumption Goods by Quality
Free goods are on the margin of utilization
4. Goods of the lowest grades, having no marginal utility, are free goods. This is a simple truth, but it has important bearings. There may be said to be an "extensive margin of utilization" of many consumption goods. The poorer grades of apples, rotting on the ground, the multitudes of waste things not valued, are on the margin of utilization. When a lower grade is used, the margin is extended. The value of goods is measured upward from the margin of utilization, but this is simply to say that their value is measured from zero upward.
Likewise, there is an intensive marginal utility in consumption goods. As the better grade of apples becomes more scarce, they will be used more sparingly and kept to satisfy only the intenser wants. The superiority of some consumption goods, either in quantity or quality, often is exactly analogous to the "differential advantage" spoken of by economists in the case of productive agents. The differential advantage of the highest grade over the grade of free goods, whose value is zero, evidently is the whole value of the highest grade.
§ II. DIFFERENTIAL ADVANTAGES IN INDIRECT GOODS
Differential advantage of agents in the quality of their products
1. Rent varies with the quality of the products yielded by agents, other things being equal. Let us take first a simple case where the agent is the sole condition of the product. If there is but one tree bearing a certain luscious fruit, or but one spring yielding a mineral water, the rent of the tree or spring being equal to the value of the products must vary as the quality of the products varies. If two or more trees are standing side by side, they will be compared with regard to the difference in the quality of their fruits. If two fields differ in quality, greater importance will be attached to the field capable of producing the better grade or variety of fruit or product. A peculiar mineral quality in the soil may impart to wine a choice flavor that can at once be recognized by experts; while other fields, distant but a few rods, cannot by any effort be made to produce wine of the same rare quality. There is said to be a marked difference in the success of vineyards lying only a short distance apart on the shores of the larger lakes of New York. Nearness to the water moderates the temperature, often prevents frosts, and hence insures the ripening and quality of the fruit. In the Santa Clara valley, as in other parts of California, there is a frostless belt, sharply marked off from the lands where it is unsafe to attempt to cultivate the delicate orange-tree and other semi-tropical plants. In manifold ways differences in geological formation affect the use of land and the success of many industries. On one side of a little creek is limestone land, on the other shale, the limestone producing a crop larger and of better quality. When the peculiar nature of the one field is found to be the cause of the exceptional quality of its fruits, the difference in value is attributed to it.
The lower grade limits the value of the higher grade