It will be noticed that the basis from which each of these measures starts is wealth. The first argues that benefit is indicated by wealth, the second that faculty is so indicated. If wealth is the basis, then the classification of made to depend on that of wealth. Such a method, although tried, has been found impracticable, because the processes of shifting render it impossible to ascertain the final incidence with sufficient accuracy for classification. It has also been suggested that we might use the different specific means employed by nations to measure benefit or faculty. But here again we meet with difficulties that are almost insuperable ; for in that case the classification will depend on the theory adopted as to the correct measures. If we adopt the benefit theory, our classification will depend on the different indices of benefit chosen. If we adopt the faculty theory, then our classification will be according to the indices of faculty. But we are not at liberty to adopt one or the other of these theories exclusively, because no nations have done so in practice, and their taxes are some of them based on the one theory, or at least best explained thereby, and some on the other, while many combine both or may be interpreted in either way. At the same time many taxes that could not be justified on either basis are retained by the nations on grounds of general expediency, because they yield considerable revenue, or because they have been long in use. If, therefore, we adopt a classification presupposing either theory, we shall find many taxes that do not conform to it. Inasmuch as no consistent plan for the measurement of taxation has been adopted by any country, no uniform method of classification upon " natural " grounds can be found.

These difficulties are inherent in the matter that we are attempting to classify. The librarian generallydesires to arrange his books according tothe subjects treated. But encyclopaedias could not be so arranged without tearing the books to pieces. We might theoretically dissect each tax, and assign its parts to the different categories according to the real nature of each part. But we gain little by this painful process. In this case classification will not help us to ascertain the real nature of the things studied.

These difficulties have not always been regarded as insuperable, and many brave attempts have been made to overcome them, but with so little uniformity as to mark the failure. There are almost as many classifications as writers. The least satisfactory of all are those that attempt to find some natural arrangement. Those which have the most apparent success accept the official names used by the treasury departments of the different nations, and give them merely such limitation as is necessary to use them scientifically.