Part of the explanation may be sought in the fact that the writers who have developed the general theory of value have not been, in general, the writers who have most elaborated the theory of the value of money. The theory of money has been for a long time a more or less isolated discipline. In Ricardo, we have an elaboration of the labor theory of value, and we also have the quantity theory of money. But it is not clear that Ricardo added anything to the quantity theory. He found it, in much the form in which he used it, in the writings of predecessors, among them Locke and Hume. Ricardo makes large use of the quantity theory as a premise, but apparently feels the theory to be so self-evident that it needs little exposition or defence at his hands. John Stuart Mill is a clear exception to the general statement. Cairnes, likewise, did treat both topics in considerable detail, but while his interest in the general theory of value was that of the theorist, his treatment of money was primarily in the spirit of the publicist, and his interest was less in the justification of the theory--which he again seems to feel needs little defence--as in its application. A similar statement may be made with reference to Jevons. He worked out his general theory of value for its own sake; his utterances on the theory of the value of money must be sought scattered through his practical writings on money. Alfred Marshall's _Principles_ (Vol. I) says almost nothing about the theory of money; his opinions on that subject are to be found in some _ex cathedra_ replies to questions from a Parliamentary Commission. The most important discussions in England of the value of money are to be found in the long polemic between the Currency and the Banking Schools, by writers who would not be listed among the makers of the general theory of value. In the United States to-day, with the exceptions of Professors Fisher and Taussig, the writers who have been interested in the general field of economic theory have done comparatively little with the value of money (_e. g._, Professors Clark and Fetter), and the writers who have been most interested in the value of money have usually not written largely on the general theory of value (_e. g._, Professors Laughlin, Scott, Kinley). Professor Kemmerer might well be included as an illustration of this last statement. His primary interest is in money, rather than general theory, even though he does precede his theory of the value of money with an exposition of the utility theory of value. In German, a similar situation obtains. Böhm-Bawerk has touched the theory of money scarcely at all. Menger has written an important article on "Geld" in the _Handwörterbuch der Staatswissenschaften_, but the important thing about this article is the theory of the origin of money, and the reader will find little on the problem of the value of money. Wieser has recently taken up the value of money (in articles published in 1904 and 1909), but no trace of his views has as yet manifested itself in the English literature on money, and the writer may here express the opinion that Wieser's contributions to the theory of money are not likely to be very influential, or to add to his reputation.[42] Austrian writers on the value of money, as Wieser and von Mises, have recognized more clearly than anyone in America or England, the essential dependence of the theory of the value of money on the general theory of value. The German writer on money who has attracted most attention recently, however, G. F. Knapp, troubles himself about the general theory of value not at all.