The study has as its field of investigation the theory of human capital, developed around 1960 by the Chicago school (Becker, 1962; Mincer, 1958; Schultz, 1961). This framework is based on an analysis of individual rational choices and should provide an explanation of the distribution of income between workers. The aim of this paper is to discuss these aspects, through a reconstruction of the evolutionary path of the concept of human capital starting from Petty's (1609) pioneering work. The micro-economic analysis based on the rational choices of the individual will be criticized, by considering the role played by the family in the decisions of an individual's educational career (Marshall, 1890). It will be also discussed the possibility of considering knowledge as a capital good which, among other things, must be able to guarantee a profit rate to its owner (Smith, 1776; J.S. Mill, 1848; Marx, 1867; Marshall, 1890; Fisher, 1906). According to this perspective, in equilibrium the rate of profit of human capital should be equal to the one realised on the physical capital. In the neoclassical framework, critical is the idea that the individual can reach adulthood without incurring in costs as in the case of a natural resources. It is precisely this assumption which allows modern theory of human capital to consider the level of education as the result of the rational choice of an individual.

Following a different approach, in a classical framework there is the idea that an improvement in the knowledge and skills of workers produces a greater wealth for society (Smith, 1776; Marx 1867). However, there is not a mechanical relationship between the contribution to production and the relative remuneration of knowledge and skills. In the spirit of classical authors, Engel (1883) proposes a model for calculating the cost of production of men based on the division of the population into three classes according to their relative wealth. Furthermore, there is no idea of a distribution of wealth among individuals that depends on private investment in knowledge and skills. The causal link is reversed, as Engel believes that only the richest class can achieve the highest level of education.In this perspective, it could be said that the production cost of the working class is a component of the subsistence wage, as the latter serves for the maintenance and reproduction of workers. In other words, workers can do their job with average efficiency and at the same time raise children that will replace them. Therefore, the adult individual is not considered a natural resource but has a production cost as if it were a "particular commodity".