The effect of moral restraint on the natural wage rate In 1798 the idea of a positive relation between real income and population growth was very old. It was the main argument of the populationists, according to whom the power of a nation depends on the number of its citizens. But also in the Netherlands, where it was believed that the power of the Republic depends on economic strength, the relation between income and population was thoroughly discussed. It did not occur to him, and neither did it to his audience, that population growth could be related to loose morals. It should be noted that the incidentally very modern immigration mechanism produces the same result economically as the Malthusian Principle.
Labour supply is a strictly increasing function of national differences in living standards.
Also Adam Smith held the opinion that population would increase with rising living standards. Smith's approach, however, is rather subtle and embedded in many qualifications. The value of children is the greatest of all encouragements to marriage . In the long run Smith's suggestion has proven to be more relevant than the Malthusian Principle. And more heuristic.