Labor, the source and determinant of value, has, _per se_, no value. Only when it is embodied in certain forms has it any value. If a man labors hard digging holes and refilling them, his labor has no value. What the capitalist buys is not labor, but labor-power. Wages in general is a form of payment for a given amount of labor-power, measured by duration and skill. The laborer sells brain and muscle power, which is thus placed at the temporary disposal of the capitalist to be used up like any other commodity that he buys. The philosopher Hobbes, in his "Leviathan," clearly anticipated Marx in thus distinguishing between labor and laboring power in the saying, "_The value or worth of a man is ... so much as would be given for the Use of his Power_." The power to labor assumes the commodity form, being at once a use-value and an exchange-value. At first sight it appears that piecework is an exception to the general rule that the capitalist buys labor-power and not labor itself. It seems that when piece-wages are paid it is not the machine, the living labor-power, but the product of the machine, labor actually performed, that is bought. Superficially, this is so, of course, but it does not affect the principle laid down, because, as a matter of fact, the piecework system is only one of the means used to secure a maximum of labor-power. The average output of pieceworkers in a trade always tends to become the standard output for the time-workers, and, on the other hand, the average wage of pieceworkers tends to keep very near the standard of time-wages.