These two principles of cost of service and value of service are directly opposed in one regard; inasmuch as the cost of service theory harks directly back to railway expenditure; while the value of service principle contemplates primarily the effect upon the railway's income account. Any charge is justified according to the latter view, which is not detrimental to the shipper as indicated by a positive reduction in the volume of business offered. No charge, on the other hand, may be deemed reasonable according to the cost of service principle, which affords more than a fair profit upon the business, regardless of its effect upon the shipper. As a matter of fact neither of these views is entirely sound by itself. Both have large elements of truth in them. Each qualifies the other. In the first place, it is to be noted that between them they fix the upper and lower limits of all possible charges. Less than the cost of service cannot be charged; else would a confiscatory rate result. This was the plea set up by the railways in the now celebrated Texas Cattle Raisers' Association case against the cancellation by the Interstate Commerce Commission of an extra charge of $1 per car for switching charges at Chicago. At the other extreme, more than the traffic will bear cannot be charged without a disproportionate decline in volume of tonnage. This would be bad business policy, as it could at once entail loss of revenue. The railway could not submit to the former alternative; it would not conceivably resort to the latter. Attempts have been made by various authors to account for the phenomena of rate making on other grounds. The German author, Sax, has sought to trace an analogy between the imposition of taxes and railway charges, alleging that both should be proportioned to what the shipper "can afford to pay," from an ethical rather than an economic point of view. Acworth interprets the phrase "charging what the traffic will bear" to mean something analogous to this. His allegation is that rate schedules are built up upon the principle of "equality of sacrifice," otherwise characterized as "tempering the wind to the shorn lamb." High class traffic contributes liberally of its abundance of value, while third class passengers and low grade tonnage are let off lightly on the ground of their poverty. Taussig in his memorable contribution to the subject[139] has, however, shown how untenable this theory of "equality of sacrifice" is. Not ethical but purely economic considerations are applicable in such circumstances except, of course, in so far as common carriers, enjoying privileges by grant of the state, may be considered as imposing taxes for the performance of a quasi-public duty. This latter test of a reasonable rate has underlaid a long line of Supreme Court decisions since the Granger case.[140] Nevertheless, as so frequently happens, legal and economic bases of judgment seem to be lacking in harmony.