Das Kapital, also called Capital. A Critique of Political Economy, is the most cited book in the social sciences published before 1950. Marx aimed to reveal the economic patterns underpinning the capitalist mode of production in contrast to classical political economists such as Adam Smith, Jean-Baptiste Say, David Ricardo and John Stuart Mill. Marx proposes that the motivating force of capitalism is in the exploitation of labor, whose unpaid work is the ultimate source of surplus value. Das Kapital proposes an explanation of the "laws of motion" of the capitalist economic system from its origins to its future by describing the dynamics of the accumulation of capital, the growth of wage labour, the transformation of the workplace, the concentration of capital, commercial competition, the banking system, the decline of the profit rate, land-rents, et cetera.