The penny letter rate is not by any means as low as the cost of the service. It is, however, not a burdensome charge in any circumstances, and, although so much greater than the cost, represents in a large number of instances much less than the full measure of benefit which the provision of the service confers on the beneficiary. This is, of course, the ordinary case of the purchaser of a commodity securing a "consumer's surplus."[739] Rates which yield a profit of 50 per cent. (pp. 76 and 311) must, however, be admitted to contain some element of taxation. In France particularly the Post Office occupies a definite place in the fiscal system.[740] There is, however, considerable diversity of opinion among economists with regard to the theoretical character of this revenue. Indeed, the general classification of public revenues is itself not yet agreed upon.[741] Under any classification there is difficulty in assigning a place for the Post Office revenue. With the simplest and most fundamental division it has been regarded as falling under one or other heading, according to the notion of the writer, or in accordance with certain changes of conception based on variations in attendant circumstances.[742] The difficulty of classification arises from the fact that of the total amount of the postage charges actually levied, only a portion can in any case be regarded as taxation. A person who purchases a commodity from the State, but in purchasing it is charged something more than its actual value, is not taxed to the extent of the whole of the amount which he is charged. There can be no taxation in that part of the amount for which he receives equivalent value in the commodity purchased. It is easy to say of the gross postal revenue that so much is tax (i.e. the net revenue), and so much is cost of service (i.e. the actual expenses), though it may not be easy to justify even this distinction;[743] but what principle is to be followed in determining whether a particular postage charge (e.g. the letter rate or the parcel rate), or any part of it, is taxation? Taxes are reckoned according to the rate of charge. Thus, the income tax is 2s. 3d. in the pound on earned incomes; but approached in this way postage is not a tax. If the charge only covers the cost of the service, there can be no tax.[744] And when there is a surplus (above normal commercial profit) it cannot be argued that the whole charge becomes a tax. The solution seems to be that in such a case it is neither tax nor industrial price. It contains elements of both, and cannot be classed wholly under either.[745]