3. _The enterpriser, looking upon the cost of most of the factors as fixed, seeks to combine them as economically as possible._ Whether the enterpriser is running a factory or a farm, is engaged in a retail or a wholesale store, is conducting a school, or a railroad, he has to solve much the same problem. By close attention, good judgment, skilful bargaining, he may be able to buy slightly cheaper than his competitors, and thus have an advantage over them at the outset. When he does this, it is usually by searching out a better market in which to buy, buying at a better time, and judging better than his competitors the quality of goods. If, in a given market at a given time, goods are sold to one more cheaply than to others, it is an act of generosity. Even the best buyers pay nearly the prevailing market price for agents. The most successful enterprisers are not found to be those paying lower wages or lower ground-rent than their competitors. It must not be forgotten that the main forces fixing the prices of agents are impersonal, and can be only slightly modified in most cases by a particular buyer. He looks therefore upon the cost of the elements as an ultimate fact which he can change little, if at all, and he shows his judgment chiefly in the selection of quality. Cost determines and limits the extent of his business and determines the price at which he sells. [Sidenote: The right proportioning of the factors] 4. _The right proportioning and skilful substitution of the factors is a delicate technical task for the enterpriser._ Good buying and good selling must precede and follow the central part of the enterpriser's task, that is, the combining of the various factors. Each factor is applied, subject to diminishing returns, up to a point where its addition will not secure the value attributed to it in its cost. The enterpriser is constantly studying the question whether the application of another unit of any one factor at the price will add to the value of the product as much or more than the cost. This calculation is made for every one of the minor factors entering into the business, and for the business as a whole. The proper proportion varies at different prices, or costs. If wages rise, "it pays" to get machinery; if wages fall, it pays to let the machinery deteriorate and to do more by hand-labor. Likewise there is constant substitution of the various materials. The right proportions change constantly with inventions. A model factory is so proportioned that the buildings hold the right number of machines, with the right amount of space for the workmen, and the right amount of power. If there is more of a single factor than the ideal proportion, it is an unnecessary cost. Even the model factory begins to be out of date almost as soon as the walls are dry, and the latest method is to build as nearly as possible on the unit system, so that new parts may be added without the loss of harmony and proportion.