Jean-Baptiste Say (1767-1832) was a Frenchman, born in Lyon who helped to popularise Adam Smith's work in France. His book, A Treatise on Political Economy (1803) contained a brief passage, which later became orthodoxy in political economics until the Great Depression and known as Say's Law of markets. Say argued that there could never be a general deficiency of demand or a general glut of commodities in the whole economy. People produce things, said Say, to fulfill their own wants, rather than those of others. Production is therefore not a question of supply, but an indication of producers demanding goods. Say agreed that a part of the income is saved by the households, but in the long term, savings are invested. Investment and consumption are the two elements of demand, so that production is demand, so it is impossible for production to outrun demand, or for there to be a "general glut" of supply. Say also argued that money was neutral, because its sole role is to facilitate exchanges: therefore, people demand money only to buy commodities. Say said that "money is a veil". To sum up these two ideas, Say said "products are exchanged for products". At most, there will be different economic sectors whose demands are not fulfilled. But over time supplies will shift, businesses will retool for different production and the market will correct itself. An example of a "general glut" could be unemployment, in other words, too great a supply of workers, and too few jobs. Say's Law advocates would suggest that this necessarily means there is an excess demand for other products that will correct itself. This remained a foundation of economic theory until the 1930s. Say's Law was first put forward by James Mill (1773-1836) in English, and was advocated by David Ricardo, Henry Thornton and John Stuart Mill. However two political economists, Thomas Malthus and Sismondi, were unconvinced.