3. _The idea of economic diminishing returns arises when man recognizes these technical facts and their relation to gratification, in his use of a limited supply of indirect agents._ All economy begins with scarcity. The varying effects produced by different agents therefore require to be studied or the sum or direct goods of enjoyment will not be as great as is possible. Waste will take place. A bridge will have its maximum use with a minimum outlay when the parts are in a certain proportion. Beyond that point, the increase of any part may add something to the usefulness of the bridge, but the agents must be taken from some other and greater use. The thought of economic diminishing returns always has reference to value. If a particular kind and amount of a certain material is used in varying combinations with other agents, the value of the added product will not always be in the same proportion to the value of the added agent. The bridge-builder must consider not only what the added material will add to strength, but what it will cost, and whether the result will justify this expense. So the economic problem of diminishing returns is more complicated than the mechanical one, for it contains not only the technical but other factors. [Sidenote: The marginal utility in goods] If the value of the product increases less rapidly than the cost of the agents successively added to secure it, a point must at length be reached where the value of the added agents and of the additional product just balance; this is called the point of marginal utility. If a certain value in labor, fertilizer, or material, be applied to an acre of land, it may be more than recovered in the value of the product. Further applications give a product increased not in equal proportion to the former yield, and so on till the value of the last-added agent just balances that of the added product. This is the best adjustment possible, and beyond this point there will be a deficit in value. Just where the equilibrium is found at any time is the margin of cultivation. The term "cultivation" is taken from agriculture but must be understood in the broader sense of utilization, as the principle is not confined to the case of land or agriculture, but applies as well to the use of furniture, books, clothing, horses, or any other indirect agents. [Sidenote: Meaning of intensive margin of utilization] [Sidenote: The extensive margin of utilization] 4. _There are two margins, the intensive and the extensive._ The margin of utilization in the case of a single piece of wealth is called the intensive margin. Any form of indirect wealth, anything kept to use, may be considered as containing a series of uses. Using one thing more and more while uniting other things with it, is using it more intensively.