Principles of Political Economy (Malthus)

Principles of Political Economy (1820) was a successful book by Thomas Robert Malthus (1766-1834). The last chapter of the book was devoted to rebutting Say's law, and argued that the economy could stagnate with a lack of "effectual demand". In other words, wages if less than the total costs of production cannot purchase the total output of industry, causing prices to fall; price falls decrease incentives to invest, creating a downward spiral.