Since the exchange value of commodities is, in fact, nothing but a mutual relation of the labors of individuals―labors which are similar and universal―nothing but a material expression of a specific social form of labor, it is a tautology to say that labor is the _only_ source of exchange value and consequently of wealth, in so far as the latter consists of exchange values. Similarly, it is a tautology to say that matter in its natural state has no exchange value, because it does not contain any labor, and that exchange value as such does not contain matter. But when William Petty calls “labor the father and earth the mother of wealth,” or when Bishop Berkeley asks “whether the four elements and man’s labour therein, be not the true source of wealth,”[7] or when the American, Thomas Cooper puts it popularly: “Take away from a piece of bread the labour bestowed by the baker on the flour, by the miller on the grain brought to him, by the farmer in ploughing, sowing, tending, gathering, threshing, cleaning and transporting the seed, and what will remain? A few grains of grass, growing wild in the woods, and unfit for any human purpose”[8]―then all these views do not refer to abstract labor as the source of exchange value, but to concrete labor as the source of material wealth; in short, to labor in so far as it produces use-values. In assuming that a commodity has use-value we assume the special usefulness and distinct fitness of the labor absorbed by it, but that is all there is to the view of labor as useful labor from the standpoint of commodity. Considering bread as a use-value, we are interested in its properties as an article of food and not at all in the different kinds of labor of the farmer, miller, baker, etc. If by some invention nineteen-twentieths of this labor could be saved, the loaf of bread would still render the same service as before. If it fell ready-made from the sky it would not lose a single atom of its use-value. While labor which creates exchange value is realized in the equality of commodities as universal equivalents, labor as a productive activity with a useful purpose is realized in the endless variety of use-values created by it. While labor which creates exchange values is _abstract_, _universal_ and _homogeneous_, labor which produces use-values is concrete and special and is made up of an endless variety of kinds of labor according to the way in which and the material to which it is applied.