usefulness cannot be measured as to quantity. It is hard to measure qualities unless they are of the same kind. But it is absolutely impossible to measure the general, abstract usefulness of different things. How do you find the different amount of usefulness contained in a piano as compared with a suit of clothes, of an extension-table as compared with an engine-boiler? How do you measure general usefulness? If you cannot measure it, it cannot serve as a measure of value. And if it cannot serve as a measure of value, it cannot be the cause of value, for we judge the cause of value from the changes in value as shown by the measure of value. We find the very existence of value only because of its measure. Besides, the residuum of general usefulness which remains after we abstract from the particular useful qualities, is not general usefulness to the parties concerned in the exchange, and who fix the exchange-value, but general usefulness to somebody, that is to society at large. For the parties exchanging the commodity it has no use-value whatsoever.
Not so with labor. When we abstract from the particular labor contained in the commodity we abstract only from the kind of labor, that is, from its quality, but not from its quantity. And it is just the quantity that we want, as the exchange of commodities is a quantitative relation. And this quantitative relation of labor exists for these very people who enter the exchange relation. Abstract, general, human labor can be measured quantitatively, and quantitatively only. That is why Marx's analysis is perfect. Abstract human labor, irrespective of the particular quantities of the labor employed to produce this commodity, abstract, human labor, whose only measure is time, is the cause and measure of exchange-value.
Marx, however, never rests his case on a purely logical argument. Logic is to him only an instrument to the proper analysis and understanding of the actual facts of "experience." We have seen that, as a "logical" proposition, usefulness is entirely eliminated from value. But we have
