We’ve now seen that each perfectly competitive producer in a perfectly competitive factor market maximizes profit by hiring labor up to the point at which its value of the marginal product is equal to its price—in the case of labor, to the point where VMPL = W. What does this tell us about labor’s share in the factor distribution of income? To answer that question, we need to examine equilibrium in the labor market. From that vantage point we will go on to learn about the markets for land and capital and about how they also influence the factor distribution of income.

Let’s start by assuming that the labor market is in equilibrium: at the current market wage rate, the number of workers that producers want to employ is equal to the number of workers willing to work. Thus, all employers pay the same wage rate, and each employer, whatever he or she is producing, employs labor up to the point at which the value of the marginal product of the last worker hired is equal to the market wage rate.

This situation is illustrated in Figure 19-5, which shows the value of the marginal product curves of two producers—Farmer Jones, who produces wheat, and Farmer Smith, who produces corn. Despite the fact that they produce different products, they compete for the same workers and so must pay the same wage rate, $200. When both farmers maximize profit, both hire labor up to the point at which its value of the marginal product is equal to the wage rate. In the figure, this corresponds to employment of 5 workers by Jones and 7 by Smith.

Figure 19-6 illustrates the labor market as a whole. The market labor demand curve, like the market demand curve for a good (shown in Figure 3-5), is the horizontal sum of all the individual labor demand curves of all the producers who hire labor. And recall that each producer’s individual labor demand curve is the same as his or her value of the marginal product of labor curve.

For now, let’s simply assume an upward-sloping labor supply curve; we’ll discuss labor supply later in this chapter. Then the equilibrium wage rate is the wage rate at which the quantity of labor supplied is equal to the quantity of labor demanded. In Figure 19-6, this leads to an equilibrium wage rate of W* and the corresponding equilibrium employment level of L*. (The equilibrium wage rate is also known as the market wage rate.)

And as we showed in the examples of the farms of George and Martha and of Farmer Jones and Farmer Smith (where the equilibrium wage rate is $200), each farm hires labor up to the point at which the value of the marginal product of labor is equal to the equilibrium wage rate. Therefore, in equilibrium, the value of the marginal product of labor is the same for all employers. So the equilibrium (or market) wage rate is equal to the equilibrium value of the marginal product of labor—the additional value produced by the last unit of labor employed in the labor market as a whole. It doesn’t matter where that additional unit is employed, since equilibrium VMPL is the same for all producers.

What we have just learned, then, is that the market wage rate is equal to the equilibrium value of the marginal product of labor. And the same is true of each factor of production: in a perfectly competitive market economy, the market price of each factor is equal to its equilibrium value of the marginal product. Let’s examine the markets for land and (physical) capital now. (From this point on, we’ll refer to physical capital as simply “capital.”)