It is of course understood that the useful effects or products of labor belong to the capitalist.  But what the worker sells, and what the capitalist buys, is not an agreed amount of labor, but the labor over an agreed period of time.  This inability to purchase labor, which is an inalienable bodily and mental function, and the necessity to purchase the power to perform it, is so fraught with consequences for the entire capitalist mode of production that it must be investigated more closely (37).