It is quite true that Mill, as an economist, was largely indebted to Ricardo; and he has so fully and frequently acknowledged the debt, that there is some danger of rating the obligation too highly. As he himself used to put it, Ricardo supplied the backbone of the science; but it is not less certain that the limbs, the joints, the muscular developments,--all that renders political economy a complete and organized body of knowledge,--have been the work of Mill. In Ricardo's great work, the fundamental doctrines of production, distribution, and exchange have been laid down, but for the most part in mere outline; so much so, that superficial students are in general wholly unable to connect his statement of principles with the facts, as we find them, of industrial life. Hence we have innumerable "refutations of Ricardo,"--almost invariably refutations of the writers' own misconceptions. In Mill's exposition, the connection between principles and facts becomes clear and intelligible. The conditions and modes of action are exhibited by which human wants and desires--the motive powers of industry--come to issue in the actual phenomena of wealth, and political economy becomes a system of doctrines susceptible of direct application to human affairs. As an example, I may refer to Mill's development of Ricardo's doctrine of foreign trade. In Ricardo's pages, the fundamental principles of that department of exchange are indeed laid down with a master's hand; but for the majority of readers they have little relation to the actual commerce of the world. Turn to Mill, and all becomes clear. Principles of the most abstract kind are translated into concrete language, and brought to explain familiar facts; and this result is achieved, not simply or chiefly by virtue of mere lucidity of exposition, but through the discovery and exhibition of modifying conditions and links in the chain of causes overlooked by Ricardo. It was in his "Essays on Unsettled Questions in Political Economy" that his views upon this subject were first given to the world,--a work of which M. Cherbuliez of Geneva speaks as "un travail le plus important et le plus original dont la science economique se soit enrichie depuis une vingtaine d'années."