David Ricardo takes up some of the topics addressed by Smith, in particular those concerning income distribution and value, with the purpose of eliminating errors and ambiguities and providing a coherent explanation of the phenomenon of income distribution which he considers ‘the principal problem in Political Economy’: Ricardo. Corn is produced under decreasing returns due to the different degrees of fertility of the lands available in the economy. Capitalists are rational: they start cultivation on the most fertile lands. They emerge as a consequence of decreasing returns that characterize agriculture. The relative price of the commodities is the variable on which the task to align the rate of profit of the gold industry to the rate of profit of the corn industry is attributed. A further element arising from the solution of the Ricardian model is the distinction between two categories of goods: one category, represented by corn, the wage-good, includes means of production of itself and of other good.