To split up in this manner the product into different parts, of which one represents only the labour previously spent on the means of production, or the constant capital, another, only the necessary labour spent during the process of production, or the variable capital, and another and last part, only the surplus labour expended during the same process, or the surplus value; to do this, is, as will be seen later on from its application to complicated and hitherto unsolved problems, no less important than it is simple.