Revision: Microeconomic Theory >> Main Market Forms and Equilibrium of a Firm Economics ISC (Commerce) Class 12 CISCE

The term ‘market’ refers to the whole region in which buyers and sellers are in close contact to effect the purchase and sale of a product.

In economics, the term market refers to the mechanism or arrangement by which buyers and sellers of a commodity are able to interact with each other for having economic exchange and are able to strike a deal about the price and the quantity to be bought and sold.

“A market is the set of all actual and potential buyers of a product.”, Phillip Kotler

“Market includes both place and region in which buyers and sellers are in free competition with one another.”, Pyle

“A market means a body of persons who are in intimate business relations and carry on extensive transactions in any commodity.”, Jevons

“A market is a centre in which forces leading to exchanges of title to a particular product operate and towards which and from which the actual goods tend to travel.”, Clark and Clark

An oligopoly is a market structure in which a small number of large firms dominate the industry. These firms sell similar or differentiated products, and each firm’s decisions (such as pricing or output) directly affect the others, making them interdependent.

According to Augustin Cournot, “Economists understand the term 'market', not any particular marketplace in which things are bought and sold, but the whole of any region in which buyers and sellers are in such close contact with one another that the prices of the same goods tend to equality easily and quickly.”

Monopolistic competition is a market structure in which the number of firms is large, there is free entry and exit of firms, and the firms produce differentiated products.

When a firm is able to sell the same product or service to two different categories of consumers at different prices, then it is known as price discrimination. Generally, a Monopoly firm is able to practice price discrimination successfully.

The act of selling the same product at different prices to different buyers is known as price discrimination.

An oligopoly is a market structure in which there are only a few big sellers.

Perfect competition is a form of market in which there are a large number of buyers and sellers and a homogeneous product is sold at a uniform price.

Product differentiation refers to differentiating the products on the basis of brand, size, color, shape, etc.

According to Chamberlin, “A General class of product is differentiated if any sufficient basis exists for distinguishing the goods of one dealer from those of another. Such a basis may be real so long as it is of importance whatsoever to buyers and leads to a preference for any variety of the product over another”.

A monopoly is a market situation in which a single firm sells a commodity, and there is no close substitute for the commodity the monopolist sells.

Monopsony refers to a situation in which there is a single buyer of a commodity and in which the entry into the market by other buyers is impossible.

• According to Mrs Joan Robinson, "Perfect competition prevails when the demand for the output of each producer is perfectly elastic."
• "Perfect competition is characterised by the presence of many firms. All of them sell identical products. The seller is the price taker." – Bilas
• "Perfect competition prevails when the demand for the output of each producer is perfectly elastic." – Mrs Joan Robinson
• "Perfect competition describes a market in which there is a complete absence of direct competition among economic groups." – Ferguson

• "A pure monopoly exists when there is only one producer in a market, there are no direct competitors." – Ferguson
• "Monopoly is a market situation in which there is a single seller, there is no close substitute for commodity it produces, there are barriers to entry." – Koutsoyiannis

"Monopolistic Competition is found in the industry where there is a large number of small sellers, selling differentiated but close substitute products." – J.S. Bain

• “Oligopoly is that situation in which a firm bases its market policy in part on the expected behaviour of a few close rivals.”
  — J. Stigler
• “An oligopoly is a market of only a few sellers, offering either homogeneous or differentiated products. There are so few sellers that they recognise their mutual dependence.” — P.C. Dooley

Monopsony is a market structure in which a single buyer (monopsonist) purchases the entire supply of a particular product or factor service, faces many sellers, and the entry of other buyers is very difficult or impossible.

"When there are exactly two sellers in the market this is a special case of oligopoly called duopoly." – Cohen and Cyret.

“An industry will be in equilibrium when there is no tendency for the size of the industry to change i.e., when no firms wish to leave it and no new firms are being attracted to it.” — Prof. Hansen

"The existence of long run industry equilibrium requires long run individual equilibrium at no profit no loss level of operation". - Leftwitch

• “Price discrimination exists when the same product is sold at different prices to different buyers.” — Koutsoyiannis
• “Price discrimination is the act of selling the same article produced under single control at a different price to the different buyers.” — Mrs. Joan Robinson

• “Selling costs are costs incurred in order to alter the position or shape of the demand curve for the product.” — E.H. Chamberlin
• “Selling costs include all expenses incurred to increase the demand for the goods.” — Robert Awh

“Production costs create utilities in order that demands may be satisfied while selling costs create and shift the demand curves themselves.” — E.H. Chamberlin

\[\text{Lerner Index}=\frac{P-MC}{P}\]

where P is the price of the product and MCMC is the marginal cost of producing one more unit.

Q + (n + 1)
where  Q = market size and n = number of sellers.

• In common language, a market is a place where buying and selling occur.
• In economics, a market is any arrangement that allows buyers and sellers to meet (physically or virtually), decide a price, and exchange a commodity or service.​
• A market can be local, national, or international.
• Essential elements of a market: commodity, buyers and sellers, area of operation, communication/contact, and price.​
• There are two main ways to define a market: geographical (place‑based) and functional (activity‑based).​
• Competition among buyers and sellers tends to produce one prevailing price for the same commodity at the same time within a market.​

• Market structure describes how a market is organised and how much price power firms have.
• There is a spectrum from perfect competition (many firms, no price power) to monopoly (one firm, high price power), with monopolistic competition and oligopoly in between.
• Perfect competition: many sellers, homogeneous product, perfect knowledge, free entry/exit, and firms are price‑takers.
• Monopoly: one seller, no close substitutes, restricted entry, high price power.
• Monopolistic competition: many sellers, differentiated products, and some price power within limits.

• Perfect competition is an ideal market where many buyers and sellers trade identical products, and no one can control price.
• Firms and buyers are price takers; the price is fixed by industry demand and supply.
• Pure competition needs 3 conditions (large numbers, homogeneous product, free entry/exit).
• Perfect competition needs 7 conditions (3 basic + perfect knowledge, factor mobility, no selling costs, no transport costs).
• The model is used as a benchmark to judge how efficient other markets are.

• Monopoly is a market structure with one seller, no close substitutes, and barriers to entry.
• Main features: single seller, no close substitutes, barriers to entry, price maker, firm = industry, and possible price discrimination.
• Types include private, public, legal, natural, simple, discriminating, and voluntary (cartel) monopolies.
• Under monopoly, AR is the market demand curve; MR lies below AR because price must fall to sell more.
• Equilibrium output is found where MC=MR; price is taken from the AR curve at that output and is usually above MC.
• Cost curves (FC, AFC, AVC, AC, MC) have the usual shapes, but MC is not the supply curve in a monopoly.
• Price discrimination allows a monopolist to charge different prices by person, place, time, or use.

• Sellers compete mainly through product features and branding, not by price alone.
• No single seller can dominate the market or set global prices.
• Customers benefit from choice but may pay more for features created through branding.

• Oligopoly: A market with a few dominant firms, high interdependence, and barriers to entry.
• Firms compete both by price and by non‑price methods (advertising, quality, branding).
• Price rigidity and non‑price competition are typical features of oligopolistic markets.

• Monopsony: one buyer, many sellers; buyer has market power.
• Monopsonist: the single powerful buyer.
• Main features: single buyer, many sellers, specialised input, low mobility of suppliers, buyer is price-maker.
• Common in labour markets (single large employer in a region; government as large employer).
• Joan Robinson is closely linked with the analysis of monopsony and imperfect competition.

• A duopoly is a market with exactly two dominant firms and is a special type of oligopoly.
• The key feature of duopoly is strong interdependence: each firm’s decisions affect the other, and each anticipates the rival’s reaction.
• Products may be homogeneous or differentiated, but only two firms control most of the market.
• Each firm faces uncertainty and cannot rely on a single, stable demand curve because demand depends on the rival’s behaviour.
• Strategic moves and counter‑moves (like price changes and advertising) are common in duopolistic markets.

• A bilateral monopoly exists when there is one seller (monopolist) and one buyer (monopsonist) in a market.​
• Both parties have strong market power and conflicting interests: the seller wants a high price, and the buyer wants a low price.​
• There is conflict over both the price and quantity of the product or factor being traded.
• Price and output are indeterminate because economic theory alone cannot predict a unique equilibrium; the outcome depends on bargaining.​
• The final price and quantity depend on the relative bargaining power of the monopolist and monopsonist.​

• Markets can be classified using different criteria: time, area, quantity, functions, legality, control, and transactions.
• Each type helps us understand how and where different products are bought or sold.

• Market size depends on product, transport, policy, and more.
• Durable, portable goods = big market.
• Perishable or hard-to-transport = small market.
• Government rules can expand or limit the market.

• The demand curve of a firm is the same as its average revenue curve.
• Perfect competition: horizontal demand curve; firm is a price taker; demand is perfectly elastic.
• Monopolistic competition: downward‑sloping but flatter demand curve; demand is more elastic due to many close substitutes.
• Monopoly: downward‑sloping and steeper demand curve; demand is less elastic because there are no close substitutes.
• Elasticity of the firm’s demand curve mainly depends on the availability of close substitutes and the degree of control over price.

• A firm is an economic unit/business that organises factors of production to produce goods and services and sells them to earn profit.​
• Firms buy factor services (land, labour, capital, entrepreneur) from households and other firms.​
• Firms transform inputs into outputs and decide what to produce, how much to produce, and at what price to sell.​
• Firms can be small (shops, small businesses) or large (big companies).
• Common types of firms are sole proprietorships, partnerships, and companies/corporations.

• Firms are assumed to mainly aim at profit maximisation.
• Economic profit = TR − TC.
• Normal profit is the minimum reward needed to keep a firm in the industry and is part of the cost.
• Pure (economic/supernormal) profit is the extra over and above all costs, including normal profit.
• Under the TR–TC approach, profit is maximum where the TR–TC gap is the largest.

• Producer’s equilibrium (TR–TC approach) is the level of output where profit (TR − TC) is maximum and any change in output reduces profit.​
• Under perfect competition, TR is a straight‑line curve from the origin because price is constant.
• The short‑run TC curve starts above the origin due to fixed costs and is S‑shaped.
• Break‑even outputs occur where TR = TC (no profit, no loss) – points B (OL) and D (ON).
• The profit‑making range of output lies between OL and ON, where TR > TC.
• Equilibrium output OM is where the vertical distance between TR and TC is greatest and, equivalently, where MR = MC.
• The TP curve is maximum at equilibrium output and is negative outside the profitable range.
• The TR–TC method is intuitive but does not directly show price per unit and makes it difficult to eyeball the exact profit‑maximising output.

• Producer’s equilibrium is the situation where a producer maximises profit or minimises loss and has no tendency to change output.
• Rule 1 (Shutdown rule): In the short run, produce only if P or AR ≥ AVC; if P < AVC, shut down.
• Rule 2 (First-order condition): Profit is maximised when MR = MC.
• Rule 3 (Second-order condition): At equilibrium, MC is rising and cuts MR from below, so MC < MR just before equilibrium and MC > MR just after equilibrium.
• Both MR = MC and MC cutting MR from below are necessary and sufficient for producer’s equilibrium under the MR–MC approach.​

• Industry determines market price via the intersection of DD and SS.
• An individual firm under perfect competition is a price-taker and faces a P = AR = MR horizontal demand curve.
• Short-run equilibrium of a firm: SMC = MR, and SMC cuts MR from below.
• The short-run supply curve of the firm is the rising part of SMC above minimum AVC.

• Long run: all factors variable; firms can freely enter or exit the industry.
• In long-run equilibrium under perfect competition:
  Each firm earns only normal profit.
  Each firm produces at the minimum point of LAC.
  Price = AR = MR = MC = minimum LAC.
• Industry is in long-run equilibrium when market demand = market supply and there is no tendency for entry or exit.
• Supernormal profits cause entry and lower prices; losses cause exit and higher prices; both processes move the industry to normal profit in the long run.

• Under perfect competition, price is determined by industry demand and supply, not by an individual firm.
• The individual firm is a price taker; the industry is the price maker.
• Products are homogeneous, and there are many small firms in the market.
• The firm’s demand curve is perfectly elastic (horizontal) at the market price, so Price = AR = MR.
• The firm can sell any quantity at the given price but cannot charge a higher price.

• An industry is a group of firms producing a homogeneous product under perfect competition.
• Industry equilibrium means no tendency for total output or number of firms to change.
• In the short run, industry can be in equilibrium even when firms earn supernormal profits or losses.
• In the long run, industry equilibrium requires:
  Industry demand = Industry supply,
  All firms in equilibrium, and
  All firms earning only normal profits (no entry, no exit).

• TVC is the sum of marginal costs of all units produced; graphically, it is the area under the MC curve between the origin and the chosen output.
• The MC curve is U-shaped due to the law of variable proportions (initial increasing returns followed by diminishing returns).
• Under perfect competition, the firm is a price taker; hence P = AR = MR and the MR curve is horizontal.
• Producer’s equilibrium (profit-maximising output) is attained where:
  MR = MC, and
  MC is rising and cuts MR from below.
• At this equilibrium output, the difference between total revenue and total cost (profit) is maximum, and the firm has no incentive to change its level of output.

• A monopolist is a single seller with no close substitutes and strong entry barriers.​
• Under monopoly, AR is downward sloping and MR lies below AR; MR is less than AR.​
• The monopolist is in equilibrium where MR = MC and MC cuts MR from below.​
• Equilibrium can be found by the TR–TC approach (maximum profit where TR − TC is highest) or the MR–MC approach (intersection of MR and MC).​
• In the short run, a monopolist may earn supernormal or normal profit or even incur losses but will produce as long as price covers average variable cost.

• Monopoly prioritizes total profit optimization over charging sky-high prices or maximizing per-unit margins.
• Balance of scale benefits vs output/price restrictions—government regulation needed (TRAI monitors telecom monopolies).

• Maximizes revenue by capturing more surplus.
• Requires monopoly + elastic differences.
• Everyday: Discounts, surges; ethical? Debated (helps access but exploits).

• Under monopolistic competition, firms sell differentiated products, so price and output are determined by each firm’s own demand and cost conditions.
• In the short run, a firm is in equilibrium where MR = MC and may earn super-normal profits, normal profits, or incur losses.
• In the long run, entry and exit of firms take place.
• Due to competition, firms earn only normal profits, where AR is tangent to LAC at equilibrium.

• What: Ads/sales expenses to shift demand right in monopolistic competition/oligopoly.
• Vs Production: Selling creates demand; production meets it (e.g., ads vs factory).
• ASC Curve: U-shaped—falls then rises per unit.
• Effect: Boosts AR, profits until marginal ad revenue = ad cost.
• Nature: Uncertain, ongoing, rival-dependent.

• Under oligopoly, price determination is uncertain due to interdependence of firms.
• Independent pricing may lead to price war or price rigidity (homogeneous products) or profit-maximising prices (differentiated products).
• Collusive pricing occurs when firms form a cartel and fix price and output jointly, though it is often unstable.
• Price leadership occurs when one firm fixes the price and others follow (barometric, dominant, aggressive, or effective), but it may fail due to cost differences, new firms, or lack of agreement.

• Sweezy explained price rigidity in oligopoly using the kinked demand curve.
• If a firm cuts price, rivals follow → demand becomes inelastic; if it raises price, rivals do not follow → demand becomes elastic.
• Due to the kink, the MR curve has a gap, so changes in cost or demand do not change price easily.
• Hence, firms prefer to stick to the prevailing price, leading to price stability in oligopoly markets.

• In collusive oligopoly, firms enter into agreements or form cartels to avoid price wars and maximise profits.
• Firms fix a common price and compete through non-price methods like advertising, product quality, and design.
• Collusion reduces uncertainty and rivalry arising from interdependence among firms.
• Cartels aim to ensure profit for all member firms, though they may differ in costs and market strategies.

• Mergers mean combining two or more independent firms into a single firm to reduce competition and increase efficiency.
• Firms merge due to technological changes, global competition, deregulation, and the need to cut costs.
• Types of mergers:
  Horizontal – firms producing the same product merge.
  Vertical – firms at different stages of production merge (upstream or downstream).
  Conglomerate – firms from unrelated businesses merge.