Classical economists such as Adam Smith (1723-1790), David Ricardo (17721823) and Karl Marx (1818-1883) have all argued in favour of (different versions of) the labour theory of value, Aristotelian reciprocity and ‘justice in exchange’. Many classical economists also believe in market equilibrium, and some believe that capitalism has a historical tendency for its overall rate of profit in the economy to fall. Marx, although a critic of the classical school in certain respects, and not a believer in market equilibrium, supports the belief on the tendency for the rate of profit to fall, and considers it the most important law of political economy, and in volume three of his Capital, edited by Friedrich Engels (1820-1895), seeks to prove it formally.