§ 2. #Revenue and protective tariffs.# An important distinction in principle is to be made between a tariff for revenue and a tariff for protection. A _revenue tariff_ is a schedule of duties on goods entering or leaving a country, so arranged that the collection of taxes causes the least possible disturbance to domestic industry. Speaking generally, the duties may be on either imports or exports; but, as export duties are unconstitutional in the United States, our tariff discussions are concerned only with import duties. The most completely revenue-yielding tariff is one touching only articles which, even at the higher prices are not in the least to be produced profitably in the home country. A _protective tariff_ is a schedule of import duties so arranged as to give appreciably higher prices to some domestic enterprises than they could obtain with free trade. It shuts out some foreign goods which would otherwise enter, an in so far it "protects" the domestic producer from the foreign competitors who would sell at lower prices than those at which he can or will sell. In other words, "protection" means governmental interference with the freedom of trade. The distinction between revenue and protective tariffs, thus clear in principle, is not always easy to make in practice. It does not lie in the intention of the taxing power, but in the actual effects produced. Most tariffs combine the characteristics both of revenue and of protective measures. A tariff that reduces imports but does not cut them off entirely may be called either a revenue tariff with incidental protection or a protective tariff with incidental revenue. The difference is one of degree. But notice particularly that the two features of protection and of revenue are mutually exclusive. To the extent that one is present the other is impossible. A tariff rate that in whole or in part excludes the foreign article to that extent affords "protection" but does not yield revenue. Whenever the government collects a cent of tariff taxes, the domestic producer in so far and as respects that unit of goods is unprotected. Likewise, whenever any domestic producer enjoys "protection" in respect to any unit of goods, importation is in so far prohibited and the government is deprived of any revenue whatever derived from the production and sale of that unit of goods.