The Demand for Resources

So far we have studied product markets, where firms sell output to households. We now turn the diagram around and look at resource (factor) markets, where firms buy the inputs — labor, land, and capital — they need to produce. Understanding resource demand explains how wages, rents, and other input prices are set, and how income is distributed among the owners of resources. This chapter focuses on the logic of resource demand and its central application, the labor market.

Derived Demand

The first key idea is that resource demand is a derived demand: firms want inputs not for their own sake but for the output they help produce. The demand for autoworkers derives from the demand for cars; the demand for farmland derives from the demand for crops. It follows that the demand for any resource depends on two things — the productivity of the resource and the market value of the product it makes. A resource is valuable to a firm precisely to the extent that it generates revenue.

Marginal Revenue Product

To decide how much of a resource to hire, the firm asks what each additional unit adds to its revenue. This is the marginal revenue product (MRP) — the extra revenue generated by employing one more unit of the resource. It equals the resource's marginal product (the extra output it produces) multiplied by the marginal revenue from selling that output.

Because of the law of diminishing returns, marginal product falls as more of the resource is added, so the MRP curve slopes downward. That downward-sloping MRP curve is the firm's demand curve for the resource: it shows how many units the firm will hire at each resource price.

Marginal Resource Cost and the Hiring Rule

On the cost side, the marginal resource cost (MRC) is the additional cost of employing one more unit of the resource. In a competitive resource market, where the firm is small relative to the market, the MRC simply equals the resource's price (the wage, for labor).

The firm maximizes profit by hiring up to the point where the revenue contributed by the last unit equals its cost — the MRP = MRC rule. If an additional worker's MRP exceeds the wage, hiring that worker adds to profit; if the wage exceeds MRP, the worker reduces profit. The optimum is where the two are equal. This is the resource-market counterpart of the MR = MC rule for output.

What Shifts Resource Demand

Because resource demand depends on productivity and product value, it shifts when either changes:

• Changes in product demand — A rise in demand for the product raises its price and thus the resource's MRP, increasing resource demand.
• Changes in productivity — More capital, better technology, or more skilled workers raise marginal product and increase resource demand.
• Changes in the prices of other resources — Inputs can be substitutes or complements; a change in one input's price can raise or lower the demand for another.

Optimal Input Combinations

When a firm uses several inputs, it must decide not only how much to produce but how to produce it. Two rules guide this choice. The least-cost rule says costs are minimized when the last dollar spent on each input yields the same marginal product, so that no rearrangement of spending could produce the same output more cheaply. The profit-maximizing rule goes further, requiring that each input be hired until its MRP equals its price (MRP = MRC for every input). A firm satisfying the profit-maximizing rule is automatically producing at least cost.

Wage Determination and Monopsony

In a competitive labor market, the wage is set by supply and demand, and each firm hires where the wage equals labor's MRP. But not all labor markets are competitive. A monopsony is a market with a single (or dominant) buyer of labor — for example, a sole large employer in a small town. Because the monopsonist faces the upward-sloping market labor supply, hiring one more worker raises the wage for all workers, so its marginal resource cost exceeds the wage. To limit that cost, the monopsonist hires fewer workers and pays a lower wage than a competitive market would. Monopsony helps explain wage-setting power and provides one rationale sometimes offered for minimum wages or unions as countervailing forces.

Why Resource Markets Matter

Resource markets do more than set input prices; they determine how the economy's income is divided among workers, landowners, and capital owners. The MRP framework links each person's earnings to the value of what their resources produce, while departures from competition — like monopsony — show why real-world earnings can diverge from that ideal. This connection between productivity and pay sets up the next chapter's questions about the distribution of income.

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Next chapter: resource markets determine how income is distributed. We examine the resulting inequality, its measurement, and the policies aimed at poverty and discrimination.

Further Listening & Reading

• 🎧 Planet Money: The Hidden Power Keeping Wages Low (NPR) — monopsony and employer power in the labor market.
• 🎧 The Indicator from Planet Money: The Labor Economics of "Alien" (NPR) — derived demand, productivity, and pay made vivid.