बाजार का सिद्धान्त (Theory of Markets) – Hindi + English Notes | UGC NET & UP PGT Economics

Syllabus scope / पाठ्यक्रम में स्थान

UP PGT Economics, Code 11: uploaded syllabus में Market Theory के अंतर्गत Perfect Competition, Monopoly, Monopolistic Competition, Duopoly और Oligopoly; साथ में Cost and Revenue curves हैं। UGC NET Economics, Code 01, Unit 1: Market Structures, competitive/non-competitive equilibria, efficiency properties और non-cooperative Game Theory हैं। नीचे five market forms common core हैं; detailed strategic games, concentration–markup links और regulation calculations NET advanced practice हैं। उपलब्ध copies की version/date स्पष्ट नहीं है; latest syllabus का दावा नहीं किया गया है।

1. Market and market structure / बाजार की मूल बातें

Market: buyers और sellers के बीच exchange तथा price determination की व्यवस्था; physical place होना जरूरी नहीं। Market structure sellers की संख्या, product differentiation, entry barriers और strategic interaction से पहचानी जाती है। Firm एक producing unit; industry संबंधित product बनाने वाली firms का समूह। Monopoly में relevant market में firm और industry coincide करते हैं।

⚠️ Trap: “Few firms” अकेले price या output नहीं बताता; Cournot और Bertrand में same number of firms के outcomes अलग हैं। Monopoly seller है; monopsony one buyer—इसे market structure के seller-side नामों से न मिलाएँ।

2. Revenue and profit rule / आगम और लाभ

Normal profit entrepreneur की opportunity cost है और economic cost में included है। Zero economic profit ≠ zero accounting profit. Differentiable interior profit optimum: MR=MC; strict local maximum की sufficient condition MR′−MC′<0. Corners, shutdown और global profit comparison भी जाँचें।

Memory: “पहले MR=MC से q, फिर AR से P.” Linear demand में slope constant है, elasticity constant नहीं। TR maximum at ε=1; profit maximum generally अलग point है।

3. Perfect competition / पूर्ण प्रतियोगिता ⭐

Assumptions: many atomistic buyers/sellers; homogeneous product; perfect information; free entry/exit; individual firm market price को influence नहीं करती। Firm demand perfectly elastic है, जबकि market demand generally downward sloping होती है। Market में D=S से P निर्धारित होता है; firm उस P पर q चुनती है।

3.1 Short run / अल्पकाल

Usual convex variable costs में positive output पर P=SMC on its rising branch, और operating revenue avoidable variable cost cover करे। यदि fixed cost unavoidable है:

Shutdown price = min AVC; break-even price = min AC. Standard SR supply is rising SMC above min AVC; at exact cutoff supply may include both zero and a positive quantity. This is an individual competitive firm’s supply rule, not a monopoly rule. Market supply is horizontal sum of firm supplies; productive inefficiency is not established merely because a short-run competitive firm is away from minimum AC.

3.2 Long run / दीर्घकाल

Positive profit → entry → market supply increases → pressure on P; losses → exit. Standard LR equilibrium has allocative efficiency P=MC and productive efficiency at min LAC, subject to no externalities/other distortions. LR industry supply: constant-cost industry horizontal; increasing-cost upward; decreasing-cost downward. Free entry does not by itself mean horizontal industry supply.

Worked graph: market P=20−Q and P=4+Q give Q=8, P=12. Firm TC=16+4q+q² gives AC=16/q+4+q and MC=4+2q; q=4, AC=MC=P=12. Two identical firms produce aggregate Q=8 in this example. The firm output axis uses q, market axis Q.

4. Monopoly / एकाधिकार ⭐

Assumptions: one seller in a relevant market; no close substitute; entry barriers; downward market demand; profit maximisation. Barriers may arise from legal protection, control of an essential input or cost advantages. A monopolist can choose a feasible point on demand; it cannot freely choose both arbitrary P and arbitrary q.

Higher ℒ means higher proportional price–cost margin. Positive MC implies an interior optimum lies in elastic demand region; MC=0 can place it at unit elasticity. Market power does not guarantee positive profit: fixed cost can make π negative. Monopoly has no demand-independent supply curve; its price–quantity decision depends jointly on demand and costs.

Numerical anchor: P=100−2Q, MC=20, no fixed cost. MR=100−4Q ⇒ Q_m=20, P_m=60, π=800. Same demand/cost competitive benchmark P=MC ⇒ Q_c=40. Monopoly CS=½(100−60)20=400; PS=800; total surplus=1200. Competitive total surplus=½(100−20)40=1600; DWL=400. Monopoly profit/transfer is not the deadweight-loss triangle.

Natural monopoly and regulation / प्राकृतिक एकाधिकार

Natural monopoly means one firm can serve relevant total demand at lower cost than splitting it among firms (cost subadditivity). Large fixed costs and declining AC over relevant demand often create it. Example C(Q)=F+cQ gives AC=F/Q+c>MC=c. Marginal-cost pricing P=c is allocatively efficient but leaves a loss F; average-cost pricing P=AC breaks even but normally leaves P>MC and less output. Subsidy, information and regulatory incentives matter.

Price ceiling / अधिकतम कीमत: a suitable binding ceiling can increase monopoly output: effective demand becomes horizontal at the ceiling up to the quantity demanded there, then follows original demand. Below relevant avoidable costs it can instead cause shutdown/shortage. ⚠️ “Every price ceiling increases supply” is false; distinguish a monopoly ceiling from a competitive-market ceiling.

5. Price discrimination / मूल्य विभेद

Different effective prices for the same good, beyond differences justified by serving costs. Conditions: some market power; ability to segment/identify or induce self-selection; limited resale/arbitrage. Price-taking homogeneous-product competition usually removes this pricing power.

Third degree with common MC: ℒ_i=1/ε_i; less elastic served market has higher price. Do not equate ARs across markets. Discrimination need not always raise total welfare; changed total output and its allocation matter. Perfect first-degree can remove quantity DWL in the standard no-externality model, while transferring surplus to the seller.

Two-part tariff: T(q)=A+pq. With identical known consumers and no resale, p=MC maximises their surplus; fixed fee A may extract that surplus while retaining participation. Heterogeneous consumers make the simple full-extraction rule unreliable.

6. Monopolistic competition / एकाधिकारात्मक प्रतियोगिता ⭐

Chamberlin model: many firms, differentiated products, relatively free entry, independent decisions with limited attention to any one rival, selling costs. Examples of differentiation: brand, quality, location and service. Products are close substitutes, not identical. A firm has downward-sloping demand, ordinarily elastic because alternatives exist.

Short run: MR=MC with positive, zero or negative economic profit. Standard long run: entry shifts firm demand until it is tangent to AC; P=AC, π=0, yet P>MC. Equilibrium is on the falling side of AC; q smaller than min-AC output = excess capacity. Zero profit does not mean P=MC or productive efficiency.

Graph construction: AC=16/q+q, MC=2q; firm demand AR=16−3q, MR=16−6q. At E, q=2 and P=AC=10; MR=MC=4. AC minimum q=4. Excess capacity=4−2=2. Demand is tangent to AC at q=2; it is not tangent at minimum AC.

Selling cost vs production cost: persuasion/information can shift demand; production cost provides output. Advertising is a standard differentiating tool here, but not unique to this market. “More elastic than monopoly” is a usual textbook tendency, not a numerical theorem for every pair of markets.

7. Duopoly and oligopoly / द्वयाधिकार और अल्पाधिकार ⭐

Few significant firms means each firm’s best action depends on rival actions. Non-collusive models optimise individually; cartel chooses joint-profit output, then allocates production. Firms may compete by quantity, price or non-price attributes. There is no single universal oligopoly equilibrium.

7.1 Common linear benchmark / जरूरी मॉडल

Cournot reaction: q₁=max{0,(A−bq₂)/(2b)}, similarly q₂. Holding rival output fixed is how a unilateral best response is calculated, not a claim that rivals never change. For n identical Cournot firms: qᵢ=A/[b(n+1)]; P=(a+nc)/(n+1). As n increases, price tends to c.

Same assumptions, output ranking: Q_cartel<Q_Cournot<Q_Stackelberg<Q_Bertrand; price ranking reverses. In this quantity-leadership benchmark, leader profit exceeds each Cournot firm’s, while follower profit is lower. Leadership advantage is model-dependent; do not extend it automatically to sequential price games.

Bertrand trap: two firms can produce P=MC in the special homogeneous, equal-cost, unconstrained-capacity benchmark. Product differentiation, capacity limits, unequal costs or search frictions can change that result. “Oligopoly always has P>MC” is false.

7.2 Cartel, price leadership and kinked demand

A cartel restricts aggregate output to raise joint profit; with multiple active plants, minimise total cost through MC₁=MC₂=MR of total output. A member may gain by expanding secretly at the agreed price; enforcement matters. Price leadership means a firm sets/announces a price followed by others; it is broader than Stackelberg’s sequential quantity model.

Sweezy kink: rivals do not match a price increase but match a cut. Demand above the prevailing price is relatively elastic; below it relatively inelastic. The kink creates a vertical gap in MR; MC shifts within that gap may leave price and output unchanged. It explains possible price rigidity, not how the initial kink price is determined.

8. Game theory, welfare and advanced NET tools

Best response: an optimal action given rivals’ actions. Nash equilibrium: each player’s strategy is a best response to the others; no profitable unilateral deviation. It need not maximise joint profit, be unique, be efficient or use dominant strategies. Dominant strategy is best regardless of what the rival does. A dominant-strategy equilibrium is Nash; converse is false.

Both prefer Low against either rival choice: 9>6 and 3>1. Nash=(Low,Low), though (High,High) has higher joint payoff. This is the prisoner’s-dilemma logic of cartel instability.

Above game: δ≥(9−6)/(9−3)=½. This is a conditional sustainability result. Finite known repetition of a stage game with a unique Nash outcome has the usual backward-induction problem for cooperation.

Efficiency, concentration and taxes

Allocative: P=MC in the basic private-good no-externality benchmark. Productive: producing at minimum feasible average cost. Product variety, innovation and distribution require separate assessment; a market label alone does not settle every welfare question.

HHI measures concentration, not market power in every market; demand elasticity and competitive conduct also matter. Do not insert a percentage-based HHI into the fractional formula without dividing by 10,000.

Tax distinction: an unavoidable lump-sum tax reduces profit but leaves MR=MC and the existing interior output choice unchanged, provided the firm continues operating. A per-unit tax t adds to MC; for linear-demand monopoly with constant c, Q=(a−c−t)/(2b), P=(a+c+t)/2. The ½ price pass-through is for this benchmark, not a universal tax theorem.

9. Economists–year–publication / नाम–वर्ष–कृति

Memory ladder: Cournot 1838 → Bertrand 1883 → Marshall 1890 → Chamberlin + Robinson दोनों 1933 → Stackelberg 1934 → Sweezy 1939 → Nash 1950. “C = quantity; B = bid/price; S = sequence.”

10. ⚠️ Exam traps / आम गलतियाँ

1. Firm vs market demand: perfect competition में horizontal firm demand; downward market demand.
2. MR=MC: interior candidate; second-order/global and shutdown checks जरूरी।
3. Monopoly P: MR–MC crossing की height नहीं; chosen q पर demand/AR की height.
4. Shutdown vs break-even: min AVC vs min AC; losses alone do not imply shutdown.
5. Normal profit: zero economic profit, not entrepreneur working for free.
6. Long-run zero profit: monopoly में जरूरी नहीं; monopolistic competition में P=AC yet P>MC.
7. Excess capacity: min-AC output minus actual firm output, not unsold stock.
8. Inelastic monopoly demand: positive MC पर standard interior profit optimum वहाँ नहीं होगा।
9. Bertrand: P=MC needs the special benchmark assumptions.
10. Cartel vs Cournot: joint optimum vs simultaneous individual best responses.
11. Kink: MR gap explains rigidity; initial price unexplained.
12. Profit transfer vs DWL: rectangle transferred to producer is not lost total surplus.
13. Discrimination: equal MR, not equal prices; welfare effect not always positive.
14. HHI units: fraction vs percentage; do not mix scales.

11. Final revision table / अंतिम दो मिनट

References / स्रोत

Uploaded NET/PGT syllabus mapping ऊपर दी गई है। Notes, worked numbers, graphs और associated 100 questions original teaching/practice material हैं; official PYQs होने का दावा नहीं है। Publication dates को original records/publisher pages से cross-check किया गया है।

• NCERT: The Theory of the Firm under Perfect Competition.
• MIT OpenCourseWare: Monopoly and Oligopoly—Monopoly I/II and Oligopoly I/II.
• BnF original Cournot book record (1838); original Bertrand review scan (1883).
• Marshall: Principles of Economics—first published 1890; linked later edition.
• Chamberlin 1933 edition record; Robinson publisher page confirming first publication 1933.
• Stackelberg publisher page—original German work 1934; linked English translation is later.
• Sweezy original publication record (1939); Nash original article record (1950).