Factor Markets

Factor Markets

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A factor market trades the services of land, labour, capital and entrepreneurship — the four factors of production. Households own these services and supply them; firms demand them to produce goods. Payments to factors are called factor incomes: rent to land, wages to labour, interest to capital, and profit to entrepreneurship.

Demand for a factor is a derived demand, pulled by the demand for the final good it helps produce. Firms hire up to the point where the Marginal Revenue Product (MRP) equals the marginal factor cost (MFC).

• MRP = MPP × MR (units of output × currency per unit)
• VMP = MPP × P, used when product market is perfectly competitive
• Equilibrium condition: MRP = MFC = Supply price
• Real wage = W / P, expressed in output units

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Demand Side: MRP and VMP

Factor demand curves slope downward because of the law of diminishing marginal returns — each extra unit of a factor adds less output than the previous one. The value of that extra output is the Marginal Physical Product (MPP) multiplied by the revenue it brings in. Under perfect competition in the product market, MR equals price P, so VMP = MPP × P. Under monopoly or monopolistic competition, MR < P, so MRP = MPP × MR lies below the VMP curve.

A firm hires a factor up to the point where MRP = MFC. For a competitive factor market, MFC equals the wage rate W, so W = MRP_L = MPP_L × MR. For a monopsonist (single buyer of labour), the supply curve slopes upward and MFC lies above it; the firm hires where MRP = MFC and pays the wage read off the supply curve — which is lower than MRP.

Supply Side and Factor Incomes

Factor	Factor income	Supply characteristic	Classical price theory
Land	Rent	Perfectly inelastic in long run	Ricardo’s theory of rent
Labour	Wages	Upward-sloping	Marginal productivity theory
Capital	Interest	Derived from savings/investment	Loanable funds theory
Entrepreneurship	Profit	Residual, bearing risk	Knight’s theory of profit

Theories of Interest

Two competing explanations dominate TNPSC questions. The Loanable Funds Theory (classical) sets equilibrium interest where the demand for investable funds meets the supply of savings. The Liquidity Preference Theory (Keynes) argues that interest is the reward for parting with liquid money, balancing transactions, precautionary and speculative money demand against the money supply controlled by the central bank.

• Distinguish transfer earnings (minimum needed to keep a factor in its current use) from economic rent (earning above that minimum).
• Pure rent exists only when supply is perfectly inelastic — closest to land in the long run.
• Quasi-rent applies to capital assets in the short run, before supply can adjust.

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Product Exhaustion and Distribution

Walras’ product exhaustion theorem states that under perfect competition, paying each factor its marginal product exactly uses up total output — there is no residual. This is the cornerstone of the Marginal Productivity Theory of Distribution, first formalised by J.B. Clark and later extended by Hicks and Samuelson. It cleanly separates functional distribution (how output is split between factors) from personal distribution (how that income ends up across households after taxes, transfers and ownership of factors).

Edge Cases and Examiner Traps

Trap	Correct treatment
Wage = MPP	Wage = MPP × MR (or × P under perfect competition)
Economic rent = land payment only	Any payment above transfer earning is economic rent, even on labour
Interest = reward for saving	Classical: price of loanable funds; Keynes: reward for parting with liquidity
Monopsony wage read off MRP curve	Wage is read off the supply curve at the MFC = MRP quantity
Land supply = perfectly elastic	Land is perfectly inelastic in the long run

Worked Illustration

Suppose a firm faces MPP_L = 5 units of output per extra worker and sells output at P = ₹40 with MR = ₹40 (perfect competition). VMP = MRP = 5 × 40 = ₹200. If the wage W = ₹160, the firm hires more workers because MRP > W. The process stops at the worker where MRP falls to ₹160. Real wage = 160 / 40 = 4 units of output per worker.

Practice Prompts

1. Why is factor demand called a “derived” demand? Use the MRP framework to show how a fall in product price shifts the factor demand curve.
2. Compare the Loanable Funds Theory and Liquidity Preference Theory of interest, and explain which one a Keynesian economist would prefer during a liquidity trap.

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