that reason he sees no inner connection between money and labor which creates exchange value, and considers money merely as an instrument introduced from outside into the sphere of exchange for purposes of technical convenience.[26] Franklin’s analysis of exchange value did not exert any direct influence on the general trend of science, because he discussed only special questions of political economy whenever there was a definite practical occasion for it. The contrast between useful work and labor which creates exchange value agitated all Europe during the eighteenth century in the form of this question: what particular kind of labor constitutes the source of bourgeois wealth? It was thus assumed that not every kind of labor which is realized in use-values or yields certain products does thereby directly create wealth. With the physiocrats, however, as well as with their opponents, the burning question was not, what kind of labor creates _value_, but which is it that creates _surplus value_. They approached the problem in its complicated form before they had solved it in its elementary form; such is the historical course of all sciences leading them by a labyrinth of intersecting paths to the real starting points. Unlike other builders, science not only erects castles in the air, but constructs separate stories of the building, before it has laid the foundation. Without dwelling any longer on the physiocrats and omitting quite a number of Italian economists who in some more or less ingenious ideas came close to a correct analysis of the nature of commodity,[27] we pass at once to the first Briton who elaborated the general system of bourgeois economics, Sir James Steuart.[28] His idea of exchange value as well as all the abstract categories of political economy still seem to be with him in the process of differentiation from the material elements they represent and therefore appear quite vague and unsettled. In one place he determines _real value by labor-time_ (“what a workman can perform in a day”), but immediately creates confusion by introducing the elements of wages and raw material.[29] In another place his struggle with the material substance of the subject he treats of is revealed even more strikingly. He calls the material of nature contained in a commodity, such as the silver in a silver plate, its “intrinsic worth,” while the labor-time contained in it he calls “useful value.” The former, he says “is ... something real in itself,” while “the value of the second must be estimated according to the labour it has cost to produce it.... The labour employed in the modification [of the substance] represents a portion of a man’s time.”[30]