During the 1820s, a setpiece intellectual discussion took place among the exponents of political economy, often called the Malthus–Ricardo debate after its leading figures, Malthus and theorist of free trade David Ricardo, both of whom had written books with the title Principles of Political Economy. Under examination were the nature and methods of political economy itself, while it was simultaneously under attack from others.[45] The roots of the debate were in the previous decade. In The Nature of Rent (1815), Malthus had dealt with economic rent, a major concept in classical economics. Ricardo defined a theory of rent in his Principles of Political Economy and Taxation (1817): he regarded rent as value in excess of real production—something caused by ownership rather than by free trade. Rent therefore represented a kind of negative money that landlords could pull out of the production of the land, by means of its scarcity.[46] Contrary to this concept, Malthus proposed rent to be a kind of economic surplus.[47]
The debate developed over the economic concept of a general glut, and the possibility of failure of Say's Law. Malthus laid importance on economic development and the persistence of disequilibrium.[48] The context was the post-war depression; Malthus had a supporter in William Blake, in denying that capital accumulation (saving) was always good in such circumstances, and John Stuart Mill attacked Blake on the fringes of the debate.[49]
Ricardo corresponded with Malthus from 1817 about his Principles. He was drawn into considering political economy in a less restricted sense, which might be adapted to legislation and its multiple objectives, by the thought of Malthus. In Principles of Political Economy (1820) and elsewhere, Malthus addressed the tension, amounting to conflict he saw between a narrow view of political economy and the broader moral and political plane.[50] Leslie Stephen wrote:
If Malthus and Ricardo differed, it was a difference of men who accepted the same first principles. They both professed to interpret Adam Smith as the true prophet, and represented different shades of opinion rather than diverging sects.[51]
It is now considered that the different purposes seen by Malthus and Ricardo for political economy affected their technical discussion, and contributed to the lack of compatible definitions.[48] For example, Jean-Baptiste Say used a definition of production based on goods and services and so queried the restriction of Malthus to "goods" alone.[52]
In terms of public policy, Malthus was a supporter of the protectionist Corn Laws from the end of the Napoleonic Wars. He emerged as the only economist of note to support duties on imported grain.[53] By encouraging domestic production, Malthus argued, the Corn Laws would guarantee British self-sufficiency in food.[54]
