548 HARVARD LAW REVIEW pression of a class of patrons; the cheapness or costliness, the necessary or luxurious character of an article served; the fact that rates elsewhere are high or low — not only do not, but should not and in some directions could not operate to overrule cost or rea- sonableness to the producer. There must always be a substantial return to the utility, if that is possible; and this could not be so if rates were limited at the upper end by any consideration of value of the service or 'reasonableness to the consumer. The return to the utihty must never be enormous, and this could not be so if rates were limited at the lower end by any such consideration. The sole primary requirement is that the return to the utihty shall be reasonable; in other words, the maximum and minimum limits of rates are fixed exclusively by cost. It does not follow that the circumstances referred to as value of the service have no effect on rates. They readily may, there are reasons why they should, and some of them undoubtedly do, operate to fix rates at a higher or lower point within the range of cost. There is no uniform rule that a reasonable return consists of a given percentage on the fair value of the property employed. On the contrary, the percentage of return upon the fair value of the property which it is reasonable for a utility to earn is agreed to be a variable percentage. Between the lowest return that is substantial and the highest that is not inordinate, there is a belt, more or less broad, of returns which are reasonable in some cir- cumstances and not in others. In accordance with what does the return which it is reasonable for a utihty to earn vary? It cannot vary in accordance with the cost of the service. The cost of the service consists of the costs of operation, maintenance, and insurance, depreciation, and the very item we are now con- sidering — a reasonable percentage on the value of the property employed. The percentage of return which is reasonable cannot depend upon itself, or upon the value of the property to which the percentage is to be apphed, or upon the size of any of the items which must be covered before a return begins to accrue — main- tenance, operating expenses, insurance, and depreciation — unless it be, in some cases, operating expenses.^^ Since it cannot normally ^ It is sometimes said that the efficiency of the company should affect the rate of return allowed; Taylor v. Northwest Light & Water Co., P. U. R. 1916 A, 372, 389,
