It was during the third medieval period that the productive forces reached a level at which capitalist relations became widespread in the midst of the feudal economy. This process is related to the emergence of the bourgeoisie, the class which owned the means and instruments of production, and the proletariat, the class of hired workers, deprived of these means and forced to sell the capitalist their labour power. The capitalist-owner of the means and instruments of pro- duction-began forcing the worker to labour more than was necessary to sustain his own life and the life of his family. As a result, surplus value was created and was appropriated by the capitalist. This appropriation of surplus value is a spe- cific form of exploitation under capitalism and is its basic law.