Let one ounce of gold, one ton of iron, one quarter of wheat and twenty yards of silk represent equal exchange values. As equivalents, in which the qualitative difference between their use-values has been eliminated, they represent equal volumes of the same kind of labor. The labor which is equally embodied in all of them must be uniform, homogeneous, simple labor. It matters as little in the case of labor whether it be embodied in gold, iron, wheat, or silk, as it does in the case of oxygen, whether it appears in the rust of iron, in the atmosphere, in the juice of a grape, or in the blood of a human being. But the digging of gold, the extraction of iron from a mine, the raising of wheat and the weaving of silk are so many kinds of labor, differing in quality. As a matter of fact, what in reality appears as a difference in use-values, is in the process of production, a difference in the work creating those use-values. Just as labor, which creates exchange value, is indifferent to the material of use-values, so it is to the special form of labor itself. Furthermore, the different use-values are the products of the work of different individuals, consequently the result of various kinds of labor differing individually from one another. But as exchange values, they represent the same homogeneous labor, i. e., labor from which the individuality of the workers is eliminated. Labor creating exchange value is, therefore, _abstract general labor_. If one ounce of gold, one ton of iron, one quarter of wheat, and twenty yards of silk are exchange values of equal magnitude or equivalents; then one ounce of gold, half a ton of iron, three bushels of wheat and five yards of silk are exchange values of different magnitudes, and this quantitative difference is the only difference of which they are capable as exchange values. As exchange values of different magnitudes, they represent greater or smaller quantities of that simple, homogeneous, abstract, general labor, which forms the substance of exchange value. The question arises, how are these quantities to be measured? Or, rather what constitutes the substance of labor, which makes it capable of quantitative measurement, since the quantitative differences of commodities in their capacity of exchange values are but quantitative differences of labor embodied in them. Just as motion is measured by time, so is labor measured by _labor-time_. Given the quality of labor, the difference in its duration is the only property by which it can be distinguished. As labor-time, labor has the same standard of measurement as the natural time measures, viz., hours, days, weeks, etc. Labor-time is the vital substance of labor, independent of its form, composition, individuality; it is its vital substance quantitatively, having at the same time its own inherent measure. Labor-time embodied in the use-values of commodities is the substance which makes exchange values and, therefore, commodities of