In the eighteenth century one of the first modern economists, Adam Smith, thought that " the whole annual produce of the land and labour of every country" provided revenue to "three different orders of people: those who live by rent, those who live by wages, and those who live by profit". Each successive stage of the industrial revolution, however, made the social structure more complicated. Many intermediate groups grew up during the nineteenth century between the upper middle class and the working class. There were small-scale industrialists as well as large ones, small shopkeepers and tradesmen, officials and salaried employees, skilled and unskilled workers, and professional men such as doctors and teachers. Farmers and peasants continued in all countries as independent groups. During the nineteenth and early twentieth centuries the possession of wealth inevitably affected a person's social position. Intelligent industrialists with initiative made fortunes by their wits which lifted them into an economic group far higher than that of their working-class parents. But they lacked social training of the upper class, who despised them as the "new rich." They often sent their sons and daughters to special schools to acquire social training. Here their children, mixed with the children of the upper classes, were accepted by them, and very often found marriage partners from among them. In the same way, a thrifty, hardworking labourer, though not clever himself, might save for his son enough to pay for an extended secondary school education in the hope that he would move in a "white-collar" occupation, carrying with it a higher salary and a move up in the social scale. In the twentieth century the increased taxation of higher incomes, the growth of the social services, and the wider development of educational opportunity have considerably altered the social outlook. The upper classes no longer are the sole, or even the main possessors of wealth, power and education, though inherited social position still carries considerable prestige. What criterion did Adam Smith seem to go by in his classification of social groups?
The amount of wealth The amount of money The social status The way of getting money