While Adam Smith had formulated very correctly the laws of production, in his way Malthus was adding to the means by which a better knowledge of the principles of distribution was to be obtained; and the next advance, owing to the sharp discussions of the time on the corn laws, was, by a natural progress, to the law of diminishing returns and rent. An independent discovery of the law of rent is to be assigned to no less than four persons,(32) but for the full perception of its truth and its connection with other principles of political economy the credit has been rightly given to David Ricardo,(33) next to Adam Smith without question the greatest economist of the English school. Curiously enough, although Adam Smith was immersed in abstract speculations, his “homely sagacity” led him to the most practical results; but while Ricardo was an experienced and successful man of business, he it was, above all others, who established the abstract political economy, in the sense of a body of scientific laws to which concrete phenomena, in spite of temporary inconsistencies, must in the end conform. His work, therefore, supplemented that of Adam Smith; and there are very few doctrines fully worked out to-day of which hints have not been found in Ricardo’s wonderfully compact statements. With no graces of exposition, his writings seem dry, but are notwithstanding mines of valuable suggestions. In the field of distribution and exchange Ricardo made great additions. Malthus and West had shown that rent was not an element in cost of production; but both Malthus and Ricardo seemed to have been familiar with the doctrine of rent long before the former published his book. Ricardo, however, saw into its connection with other parts of a system of distribution.(34) The Malthusian doctrine of a pressure of population on subsistence naturally forced a recognition of the law of diminishing returns from land;(35) then as soon as different qualities of land were simultaneously cultivated, the best necessarily gave larger returns than the poorest; and the idea that the payment of rent was made for a superior instrument, and in proportion to its superiority over the poorest instrument which society found necessary to use, resulted in the law of rent. Ricardo, moreover, carried out this principle as it affected wages, profits, values, and the fall of profits; but did not give sufficient importance to the operation of forces in the form of improvements acting in opposition to the tendency toward lessened returns. The theory of rent still holds its place, although it has met with no little opposition.(36) A doctrine, quite as important in its effects on free exchange, was clearly established by Ricardo, under the name of the doctrine of “Comparative Cost,” which is the reason for the existence of any and all international trade.