use-values of commodities is the substance which makes exchange values and, therefore, commodities of them and at the same time serves to measure definite quantities of their value. Corresponding quantities of different use-values, in which the same quantity of labor-time is embodied, are equivalents; or, to put it in another form, all use-values are equivalents when taken in proportions containing the same quantity of expended, materialized labor-time. As exchange values, all commodities are but definite measures of congealed labor-time.
To understand how exchange value is determined by labor-time, the following main points must be kept in mind: The reduction of labor to simple labor, devoid of any quality, so to speak; the specific ways and means by which exchange—value-creating, i. e., commodity producing labor becomes social labor; finally, the difference between labor as the producer of use-values, and labor as the creator of exchange values.
In order to measure commodities by the labor-time contained in them, the different kinds of labor must be educed to uniform, homogeneous, simple labor, in short, to labor which is qualitatively the same, and, therefore, differs only in quantity.
This reduction appears to be an abstraction; but it is an abstraction which takes place daily in the social process of production. The conversion of all commodities into labor-time is no greater abstraction nor a less real process than the chemical reduction of all organic bodies to air. Labor, thus measured by time, does not appear in reality as the labor of different individuals,
