It is not unimportant to bear in mind that much the same principle as that which we have discussed is applied in regard to indirect taxation, or the taxation of commodities.[32] What an article will bear--in other words what the owner can with convenience pay--is a rule alike applicable to taxation and railway rates. In more civilised countries articles of prime necessity are not taxed, or very little; articles of luxury and of great value are taxed more. A distinction is made between wheat and tobacco, sugar and wine; and whenever it is practicable, without opening the door to fraud, to put indirect taxes on _ad valorem_ basis, it is done. A similar rule is observed, so far as possible, with respect to direct taxation. Income tax, for example, is payable only by those whose incomes exceed £150. An endeavour is made to obtain the revenue of the country from the persons who can best afford to pay, and to levy it upon articles, the taxation of which will, to the least practicable extent, be a burden on the trade of the country. To fix railway rates on any other principle than that described above would be much like raising the national revenue from all persons alike, rich or poor, to impose the Customs and Excise upon all commodities, whether articles of luxury or necessity, and irrespective of their value. [32] See Ricardo (Principles of Political Economy and Taxation, 3rd Section, page 144): “Of all commodities none are perhaps so proper for taxation as those which, either by the aid of nature or art, are produced with peculiar facility. Taxes on luxuries have some advantage over taxes on necessaries, they are generally paid from income, and therefore do not diminish the productive capital of the country.” See also Leroy Beaulieu, _Science des Finances_, vol. i.