In 1803, Thomas Robert Malthus (1766-1834) published a second edition of his An Essay on the Principles of Population, a work that had been first published anonymously five years earlier. The main tenets of his argument were radically opposed to contemporary thinking. He drew attention to the consequences of untrammelled population growth, arguing that it would double every twenty-five years and that existing resources would not rise sufficiently to support such growth. Although the ultimate check on population for Malthus appeared to be want of food arising from the different ratios according to which population and food supplies increased, the immediate checks ‘are all resolvable into moral restraint, vice and misery’. Of these, the ‘positive checks’, as Malthus called them, included
...all unwholesome occupations, severe labour and exposure to the seasons, extreme poverty, bad nursing of children, great towns, excesses of all kinds, the whole train of common diseases and epidemics, wars, plague and famine.
The ‘preventive checks’ could largely be equated with ‘restraint from marriage which is not followed by irregular gratifications’, while
...promiscuous intercourse, unnatural passions, violations of the marriage bed and improper arts to conceal the consequences of irregular connections, are preventive checks that clearly come under the head of vice.
In England, Malthus argued, the checks on population were much affected by social class, the opportunities for employment and the physical, especially urban, environment. Self-imposed restraint on marriage operated with ‘considerable force throughout all the classes of the community’. The population model Malthus developed was one in which the rate of demographic growth was influenced by mortality, fertility and net migration. When the rate of population growth begins to rise there will be an increase in the price of food that will reduce the level of real wages. Lower real wages might lead to increased mortality or affect the prospects of marriage that will automatically increase the level of temporary or permanent celibacy. As a result, fertility will fall and the growth of population slow down as it would if mortality were to be increased. This is called a self-regulation or homeostatic system.
There is much in what Malthus wrote that is relevant to the post-1830 period but during the nineteenth century ways were found to escape from the weight of Malthus’ law. First, the association between population growth rates and food prices appears to have been broken even during Malthus’ lifetime. Secondly, while the relationship between mortality and real wages persisted, the latter began a long-term improvement. Mortality was probably reduced as a result, though difference between classes persisted. Improved standards of living were only one of many potential reasons for falling mortality. Thirdly, marital fertility took the place of nuptiality as the principle influence on changes and variations in general levels of fertility. Family limitation came to be widely practised. Finally, the closed system described by Malthus was thrown open to new forms of destabilising influences. Cities grew at the expense of villages and the Empire at the expense of Britain.
 Malthus, T.R., An Essay on the Principle of Population, Or, A View of Its Past and Present Effects on Human Happiness: With an Inquiry Into Our Prospects Respecting the Future Removal Or Mitigation of the Evils which it Occasions, various editions. Winch, Donald, (ed.), An Essay on the Principle of Population, (Cambridge University Press), 1992 is an annotated version of the 1803 edition while Gilbert, Geoffrey (ed.), An Essay on the Principle of Population, (Oxford University Press), provides an accessible copy of the 1798 edition. Winch, D., Malthus, (Oxford University Press), 1987 is a good short discussion.
 Ibid, Winch, Donald, (ed.), An Essay on the Principle of Population, p. 23.
 Ibid, Winch, Donald, (ed.), An Essay on the Principle of Population, p. 24.
 See, Komlos, John, ‘The industrial revolution as the escape from the Malthusian trap’, Journal of European Economic History, Vol. 29, (2000), pp. 307-331 and Thomas, Brinley, ‘Escaping from constraints: the industrial revolution in a Malthusian context’, in Rotberg, R.I. and Rabb, Theodore Kwasnik, (eds.), Population and history: from the traditional to the modern world, (Cambridge University Press), 1986, pp. 169-193.