Malthus was an English reverend (1766-1843), who in his book “An Essay on the Principles of Population,” wrote an argument against his contemporary Mr. Godwin, who believed in unlimited population growth. Malthusian population theory warned of the possibility, that while the population grew geometrically, food resources grew only in arithmetical proportion, thus creating the conditions for a shortage in the long term that would require an adjustment in the birth rate. This law of Malthus’s population was severely criticized by Karl Marx, another heterodox economist from the Classical school of economics, who called the parish of Albury “advocate of the bourgeoisie.” The principles of Malthus had great influence on the thinking of Darwin and Wallace about the struggle for life as the source of the natural selection of the strongest.
In his “Principles of Political Economy”, Malthus explained how he was against Say’s Law, by considering demand as an aggregate. Thus, if wages were to be mantained at a subsistence level, aggregate demand would drop. Therefore there would be a production surplus, idea that would be used by J.M. Keynes in his “The General Theory of Employment, Interest and Money”.