A particular application of marginalist analysis (a refinement of marginal-productivity theory) became known as human-capital theory. It has since become a dominant means of understanding how wages are determined. It holds that earnings in the labour market depend upon the employees’ information and skills. The idea that workers embody information and skills that contribute to the production process goes back at least to Adam Smith. It builds on the recognition that families make a major contribution to the acquisition of skills. Quantitative research during the 1950s and ’60s revealed that aggregate growth in output had outpaced aggregate growth in the standard inputs of land, labour, and capital. Economists who explored this phenomenon suggested that growth in aggregate knowledge and skills in the workforce, especially those conveyed in formal education, might account for this discrepancy. In the early 1960s the American economist Theodore W. Schultz coined the term human capital to refer to this stock of productive knowledge and skills possessed by workers.

The theory of human capital was shaped largely by Gary S. Becker, an American student of Schultz who treated human capital as the outcome of an investment process. Because the acquisition of productive knowledge is costly (e.g., students pay direct costs and forego opportunities to earn wages), Becker concluded that rational actors will make such investments only if the expected stream of future benefits exceeds the short-term costs associated with acquiring the skills. Such investments therefore affect one’s “age-earnings profile,” the trajectory of earnings over one’s lifetime. Those who leave school early, for example, earn market wages for more years on average than those who take advantage of extended schooling, but those in the latter group typically earn higher wages over their lifetimes. Under certain conditions, however, the total lifetime earnings of the two groups can be the same, even though the highly educated tend to earn higher wages when they work.

Investments in human capital depend upon the costs of acquiring the skills and the returns that are expected from the investment. Families can influence these variables. Wealthier families, for example, can lower the costs of human-capital acquisition for their children by subsidizing their education and training costs. In addition, wealthier and better-educated parents can shape the tastes and preferences of their children by instilling in them a high regard for education and a desire to perform well in school. This translates into a higher rate of return on knowledge and skills relative to that of children from less-advantaged families. Thus, parents and guardians play an essential role in creating advantages for their children by encouraging them to acquire substantial stocks of human capital. Ultimately, it is human capital which has value in labour markets.

Becker introduced the important distinction between “general” human capital (which is valued by all potential employers) and “firm-specific” human capital (which involves skills and knowledge that have productive value in only one particular company). Formal education produces general human capital, while on-the-job training usually produces both types. To understand investments in human capital by employees and employers, one must pay attention to the different incentives involved. In all cases, employers are loathe to provide general skills, because employees can use them in other firms. Conversely, employees are less inclined to invest in firm-specific human capital without substantial job security or reimbursement. These issues lie at the heart of many contemporary analyses of employment relations.

Analyses of economic distribution appear in David Ricardo, Principles of Political Economy and Taxation, 3rd ed. (1821, reissued 2004), the classical subsistence theory of wages; Karl Marx, Das Kapital, vol. 1 (1867), published in English as Capital: A Critical Analysis of Capitalist Production, trans. by Samuel Moore and Edward Aveling, vol. 1 (1886, reissued 1974), also available in many later editions, treating the process of distribution as pure conflict; John Bates Clark, Distribution of Wealth (1899, reissued 2005), the classic work on marginal-productivity theory; Frank H. Knight, Risk, Uncertainty, and Profit (1921, reissued 2006), an analysis of profits viewed as a result of imperfect foresight and as a remuneration for risk bearing; Joseph A. Schumpeter, The Theory of Economic Development (1934, reprinted 1983; originally published in German, 1912), an analysis of economic development as a result of the innovations of entrepreneurs; Paul H. Douglas, The Theory of Wages (1934, reprinted 1964), marginalist theory based on statistical research which sets forth the famous Cobb-Douglas function; K.J. Arrow et al., “Capital-Labor Substitution and Economic Efficiency,” The Review of Economics and Statistics, 43(3):225–250 (August 1961), an econometric study; J.R. Hicks, The Theory of Wages, 2nd ed. (1964, reissued 1973), a sophisticated treatment of marginal-productivity theory; and Nicholas Kaldor, Essays on Value and Distribution, 2nd ed. (1980), chapter 10, “Alternative Theories of Distribution,” a discussion of various theories from Ricardo to Keynes. Dan Usher, The Economic Prerequisite to Democracy (1981), suggests that democracy requires broad agreement on how an economic system will distribute wealth. Other works in this area are Alan S. Blinder, Toward an Economic Theory of Income Distribution (1974); and Ronald G. Ehrenberg and Robert S. Smith, Modern Labor Economics: Theory and Public Policy, 9th ed. (2006). Gary S. Becker, Human Capital: A Theoretical and Empirical Analysis with Special Reference to Education, 3rd ed. (1993), presents the modern form of the theory of human capital.