Malthus wrote two books, "An Essay on the Principle of Population" (published in 1798) and "Principles of Political Economy" (published in 1820). The second book which was a rebuttal of Say's law had little influence on contemporary economists. However, his first book became a major influence on classical liberalism. In that book, Malthus claimed that population growth would outstrip food production because population grew geometrically while food production grew arithmetically. As people were provided with food, they would reproduce until their growth outstripped the food supply. Nature would then provide a check to growth in the forms of vice and misery. No gains in income could prevent this and any welfare for the poor would be self-defeating. The poor were in fact responsible for their own problems which could have been avoided through self-restraint.