Tax incidence and monopsony: who really pays when market rules change?

Tax incidence follows the response of buyers and sellers

Tax incidence asks how the economic burden of a tax is distributed after the market responds. In a competitive model, a per-unit tax creates a wedge between the price buyers pay and the price sellers receive. The quantity adjusts until buyer demand and seller supply agree at those two prices. Calling the tax a seller tax does not make the buyer’s price stay fixed.

Open the tax-incidence simulation and compare buyer and seller prices against the no-tax baseline. OpenStax’s discussion of elasticity and pricing explains why responsiveness matters for tax burdens. The Modic curves are deliberately fixed linear schedules. Its burden split is a consequence of those slopes, not an estimate for a particular country, product or proposed tax.

Worked example: follow a thirty-unit tax

Use the teaching demand P = 100 − Q and supply P = 2Q. The currency and quantity units are invented so the arithmetic can be checked without relying on external measurements.

1. With no tax, equate 100 − Q and 2Q. Quantity is 100/3 and the common price is 200/3. Save this common price as the baseline for both sides.
2. Add a thirty-unit tax wedge. Solve 100 − Q = 2Q + 30 to obtain Q = 70/3. Buyers pay 230/3 while sellers receive 140/3; the difference between those prices is exactly thirty.
3. Compare with the baseline. Buyers pay ten more per unit and sellers receive twenty less. Revenue is 30 × 70/3 = 700. The lost-trade triangle is a separate efficiency measure, not another recipient of that revenue.

Monopsony changes the cost of adding a worker

Monopsony concerns buyer-side market power. In the simple uniform-wage labor model, a large employer faces an upward-sloping labor-supply curve. Hiring more workers requires a higher wage, and the employer pays that wage to its existing workers as well. The marginal expenditure on another worker therefore exceeds the wage of that worker alone.

The monopsony hiring simulation separates wage, marginal labor cost and marginal revenue product. OpenStax’s treatment of imperfectly competitive labor markets gives the textbook context. With the toy schedules, profit-maximising employment is thirty, compared with forty-five at the competitive intersection. Those values depend on the supplied functions and uniform-wage rule; a single employer in a town is not enough information to estimate an actual wage markdown.

Gresham’s law makes the exchange rule explicit

A related lesson about constraints appears in Gresham’s-law spending game. Two coins have equal face values under a compulsory exchange rule but different commodity values. A spender can conserve the more valuable material by using the lower-value coin at the fixed face-value rate. The mechanism depends on how coins are accepted and valued in transactions.

Allow commodity-based pricing and the spending comparison changes. This is why a slogan about bad money driving out good needs its institutional qualifications. It does not show that inferior products always eliminate superior ones, nor does it explain every change in currency use. Like the tax wedge and uniform-wage rule, the exchange convention belongs inside the model rather than in a footnote added after the conclusion.

Questions for evaluating a market claim

Before accepting a conclusion about who pays, ask for the mechanism that moves the burden. These checks help identify which extra evidence would make the explanation useful.

• Separate the person who legally remits a payment from the person whose real income or surplus changes after prices and quantities adjust.
• Identify alternatives on both sides: substitute products, other employers, other workers, different locations and the time needed to switch.
• State the pricing rule. Are wages uniform, prices negotiated, coins accepted at face value, or contracts fixed for a period?
• Keep revenue transfers, lost trades and other welfare consequences separate. Do not add them indiscriminately or assume a model’s efficiency measure captures every policy objective.

Translate the model into an evidence request

For a proposed product tax, useful evidence includes how demand and supply respond over the relevant time horizon. For an employment claim, examine realistic outside options, hiring patterns and wage-setting institutions. For a currency claim, examine acceptance rules and relative valuations. Each question is more specific than asking whether markets generally work well.

If your question concerns economy-wide output rather than one market, the expenditure-multiplier activity and Solow-growth model change the unit of analysis. They also change the assumptions. Move between models deliberately: a short-run spending chain, a long-run capital path and a single-market tax wedge do not answer the same policy question.