Chapter 1 — MICROECONOMIC THEORY (40 Marks)

What is microeconomics?
Microeconomics is the branch of economics that examines the behaviour of individual decision-making units: consumers, firms and owners of resources. It analyses how these agents make choices under scarcity and how their interactions determine market outcomes. Microeconomics builds models that isolate key variables so we can understand cause-effect relationships and predict responses to changes in prices, incomes, technology or policy.

Core concepts
At the heart are concepts such as scarcity, choice, opportunity cost, marginal analysis and equilibrium. Scarcity means wants exceed available resources, making choices necessary. Opportunity cost is the value of the next best alternative foregone. Marginal analysis evaluates changes at the margin—how one extra unit affects benefits and costs—which is central to optimisation decisions by consumers (maximising utility) and firms (maximising profit).

Method and tools
Microeconomics uses both graphical and algebraic tools. Graphs like supply and demand, cost curves, indifference curves, isoquants and Edgeworth boxes visualise relationships and equilibrium. Algebraic functions express demand, supply, cost and production relations to perform exact calculations. Comparative statics are used to study how equilibrium values change when parameters change, such as taxes or tastes.

Assumptions and limitations
Micro models often assume rational behaviour, complete information, and competitive markets to obtain clear results. These assumptions simplify analysis but may not always hold. When assumptions fail—due to market power, externalities, asymmetric information or public goods—markets may not deliver efficient outcomes and policy interventions may be warranted.

Applications and importance
Microeconomic theory explains everyday phenomena: why price of vegetables rises after a poor harvest; why a firm hires more workers when output increases; how a tax affects prices and welfare. It underpins public policy choices—tax design, subsidies, competition policy and regulation. For students, learning microeconomics develops analytical thinking useful for business, governance and personal financial decisions.

How to study this unit
Begin with clear definitions, practise drawing labelled diagrams, and derive results algebraically where required. For each topic, connect theory to simple real-life examples and consider policy implications. Use marginal reasoning consistently and remember to state ceteris paribus (other things equal) when analysing comparative statics.

Law of demand and intuition
The law of demand states that, ceteris paribus, quantity demanded of a good decreases as its price increases and increases as its price falls. The intuitive reasons are twofold: substitution effect and income effect. The substitution effect arises when a good becomes relatively more expensive, so consumers switch to cheaper alternatives. The income effect occurs because a price rise reduces real income, lowering purchasing power and thus reducing demand for normal goods.

Demand schedule and curve
A demand schedule is a table that lists quantities demanded at different prices. When plotted with price on vertical axis and quantity on horizontal axis, it produces the demand curve. For most goods this curve slopes downward from left to right. The slope and shape depend on preferences, availability of substitutes, and income levels.

Determinants of demand
Demand for a good depends on its price, consumers' income, tastes and preferences, prices of related goods (substitutes and complements), expectations about future prices or incomes, population or market size, and government policies (taxes, subsidies). A change in any of these determinants other than the good's own price causes the entire demand curve to shift.

Normal vs inferior goods
When income rises, demand for normal goods increases; these goods have positive income elasticity. Inferior goods see demand decrease when income rises because consumers switch to higher-quality alternatives. Understanding this distinction is vital for predicting how demand shifts with economic growth.

Related goods: substitutes and complements
Substitutes are goods that serve similar purposes: an increase in the price of one raises demand for its substitute (positive cross-price elasticity). Complements are goods used together: an increase in the price of one lowers demand for the other (negative cross-price elasticity). For example, if petrol price rises, demand for bicycles (a substitute) may increase; if car prices fall, demand for petrol (a complement) may increase.

Movements along vs shifts of demand
A movement along the demand curve is caused by a change in the good’s own price. A shift of the demand curve occurs when a determinant other than price changes. It is important to label diagrams carefully to distinguish a price-induced movement from a demand shift caused by, say, income changes or advertising.

Deriving individual and market demand
Individual demand curves can be horizontally summed to get market demand. Market demand reflects aggregate behaviour and is generally less elastic than individual demand if consumers vary in preferences. Practice adding schedules or integrating individual demand functions to form market demand.

Policy relevance
Understanding determinants helps policymakers predict the impact of income support, taxation, and advertising. For firms, knowledge of determinants guides pricing strategies and product positioning. For consumers, it clarifies how their choices respond to changes in prices and incomes.

Law of supply and why it holds
The law of supply states that, ceteris paribus, quantity supplied of a good increases as its price rises and decreases as the price falls. Higher prices make production more profitable, encouraging firms to increase output or induce new firms to enter the market. The upward-sloping supply curve reflects this positive relationship between price and quantity supplied.

Supply schedule and curve
A supply schedule lists quantities suppliers are willing to sell at various prices. Plotting the schedule yields the supply curve, which is typically upward sloping. The steepness depends on how easily production can be increased—this is supply elasticity. When firms face capacity constraints or fixed inputs in short run, supply is less responsive; in the long run supply is often more elastic.

Determinants of supply
Key determinants include price of the good, input costs (wages, raw materials), technology, taxes and subsidies, expectations about future prices, number of sellers in the market and natural conditions (weather, floods). A change in any factor other than the price causes the supply curve to shift. For example, a technological improvement lowers per-unit production costs and shifts supply right.

Short-run vs long-run supply
In the short run some inputs (like capital) are fixed; firms can only change variable inputs such as labour. Therefore short-run supply curves reflect capacity constraints and typically are steeper. In the long run all inputs are adjustable and firms can enter or exit the industry, making long-run supply more elastic and altering industry output significantly in response to sustained price changes.

Individual and market supply
Market supply is the horizontal sum of individual firms' supplies. If individual supply curves are identical, summation is straightforward; if not, add quantities at each price. Industry supply in the long run depends on entry/exit and whether input prices change with industry expansion, giving different long-run supply shapes: horizontal for constant-cost industries, upward sloping for increasing-cost industries.

Supply shocks and policy
Supply shocks like crop failures or oil disruptions shift supply left, raising prices and lowering quantity. Policy instruments such as subsidies to producers shift supply right, lowering price for consumers and increasing quantity. Understanding supply determinants is crucial for analysing inflationary pressures and designing interventions during shortages.

Elasticity of supply
Supply elasticity measures responsiveness of quantity supplied to price change and determines how burden of taxes is shared and the magnitude of price adjustments. Highly elastic supply means producers can quickly adjust output; inelastic supply implies little response to price.

Definition of market equilibrium
Market equilibrium is a price-quantity pair where quantity demanded equals quantity supplied. At this equilibrium there is no excess demand or supply; price has no immediate tendency to change if other conditions remain the same. Graphically it is the intersection point of the market demand and supply curves.

Finding equilibrium algebraically
When demand and supply functions are given, set Q_d(P) = Q_s(P) and solve for equilibrium price P*. Substitute P* back into either function to get equilibrium quantity Q*. This method is useful when functions are linear or simple non-linear forms, and it helps perform comparative statics calculations precisely.

Adjustment process
If the market price is above equilibrium, quantity supplied exceeds quantity demanded, creating a surplus. Competition among sellers pushes price down. If the price is below equilibrium, shortage occurs and buyers bid the price up. These adjustment forces lead the market to move toward equilibrium in absence of external shocks.

Comparative statics methodology
Comparative statics examines how equilibrium responds when exogenous variables change, like income, technology, taxes or preferences. Practically, shift the appropriate demand or supply curve and determine the new intersection. Use algebra for precise direction and magnitude when functions are specified. For simultaneous shifts of demand and supply, the change in price and quantity may be ambiguous in sign unless one shift dominates; compute using functions to resolve ambiguity.

Examples of comparative statics
1) A subsidy to producers shifts supply right: equilibrium price falls and quantity rises. 2) An increase in income for a normal good shifts demand right: both equilibrium price and quantity rise. 3) A rise in input costs shifts supply left: price increases and quantity falls. When demand and supply both increase, quantity rises but price change depends on relative shift magnitudes.

Policy applications
Comparative statics is used to evaluate taxes, subsidies and price controls. For instance, a per-unit tax on producers shifts supply left creating a higher price for buyers and lower equilibrium quantity; the tax burden is shared between consumers and producers depending on elasticities. Price ceilings (rent control) and price floors (minimum support price) create persistent excess demand or supply, respectively.

Limitations
Comparative statics compares two equilibria without describing transition dynamics. For inter-temporal or path-dependent questions, dynamic modelling is required. Also, the ceteris paribus assumption must be acknowledged: real economies often face multiple simultaneous shocks.

Meaning of elasticity
Elasticity is a numerical measure of responsiveness. Price elasticity of demand (PED) measures the percentage change in quantity demanded resulting from a one percent change in price. It helps answer whether consumers or producers respond strongly or weakly to price changes, which matters for revenue, taxation and market adjustments.

Types of elasticities
Price elasticity of demand can be perfectly elastic (infinite), elastic (>1), unitary (=1), inelastic (<1) or perfectly inelastic (zero). Cross-price elasticity measures how quantity demanded of good X responds to price change in good Y: positive for substitutes and negative for complements. Income elasticity measures response of demand to changes in income: positive for normal goods and negative for inferior goods.

Methods of computation
For discrete changes, arc (midpoint) elasticity is commonly used: PED = (ΔQ/average Q) ÷ (ΔP/average P). For infinitesimal changes, point elasticity uses calculus: PED = (dQ/dP) * (P/Q). For linear demand, elasticity varies along the curve even though slope is constant; at high prices elasticity tends to be elastic and at low prices inelastic.

Elasticity of supply
Price elasticity of supply measures responsiveness of quantity supplied to price changes. Short-run supply tends to be less elastic because of fixed inputs and capacity constraints; in the long run supply is usually more elastic as firms adjust plant size and resources can move into the industry.

Determinants of elasticity
For demand: availability of close substitutes, proportion of income spent on the good, necessity versus luxury, time horizon and definition of the market (narrow markets are more elastic). For supply: time period, ease of factor mobility, spare capacity, and ability to store goods determine elasticity.

Applications
Elasticities inform business pricing decisions (if demand is inelastic raising price raises revenue), tax incidence (the more inelastic side bears greater tax burden), and welfare analysis (deadweight loss from taxation is larger when demand and supply are elastic). They are also crucial for forecasting responses to policy changes, such as subsidies or import tariffs.

Interpreting signs and magnitudes
Demand elasticities are usually negative because of the inverse price-quantity relation; economists often report absolute values. Cross-price and income elasticities can be positive or negative indicating substitutes/complements and normal/inferior status. Magnitude indicates sensitivity: a PED of -2 means a 1% price rise reduces quantity by 2%.

Utility and its measurement
Utility represents satisfaction derived from consuming goods. In early micro theory utility was treated as cardinal—a measurable number of 'utils'—allowing the concepts of total utility (TU) and marginal utility (MU). Although utility is ultimately ordinal (rankings matter more than numbers), cardinal concepts give useful intuition about consumer choice and demand.

Total and marginal utility
Total utility is the aggregate satisfaction from consuming a given quantity. Marginal utility is the additional satisfaction from consuming one extra unit: MU = ΔTU/ΔQ. The law of diminishing marginal utility states that as consumption of a good increases, the additional utility from each extra unit typically decreases beyond some point, holding other things constant.

Consumer equilibrium under cardinal utility
With a fixed income and two goods, a consumer maximises total utility by allocating expenditure so that the marginal utility per rupee of expenditure is equal across goods: MU_x / P_x = MU_y / P_y. This rule ensures no reallocation of spending can increase total utility: if MU_x/P_x > MU_y/P_y, buying more of X and less of Y raises utility.

Income and substitution effects
When price changes, the MU/P rule helps explain how consumption adjusts. A price fall in X increases MU_x/P_x, leading substitution toward X; simultaneously the consumer’s real income rises changing demand further (income effect). For normal goods substitution and income effects work in same direction; for inferior goods they oppose each other.

Limitations of cardinal approach
Cardinal measurement of utility is convenient but unrealistic: utility cannot be directly observed or precisely measured. Therefore economists moved to ordinal approaches (indifference curves) that represent preferences through rankings rather than numeric utilities, preserving the MU/P intuition via marginal rate of substitution (MRS) equals price ratio at optimum.

Connection to demand
The MU/P condition yields individual demand functions: as price changes, the consumer reoptimises, tracing out how quantity demanded varies with price. This forms the basis for deriving demand curves from preference and budget constraint assumptions.

Applications and policy
Utility analysis explains effects of subsidies, taxation, and income transfers on consumption. It helps evaluate welfare changes and design policies that improve social welfare, such as progressive transfers or price supports for necessities for low-income households.

Basics of indifference curve analysis
Indifference curve (IC) analysis models consumer preferences ordinally. An IC shows combinations of two goods that yield equal satisfaction. Higher ICs represent higher utility levels. Indifference curves are used together with the budget line to derive the consumer's optimal choice without assigning numerical utility values.

Properties of indifference curves
Important properties: ICs slope downward because more of one good must compensate for less of the other to keep utility constant; they do not intersect (otherwise preferences would be inconsistent); they are convex to the origin reflecting diminishing marginal rate of substitution (MRS) — as a consumer substitutes one good for another, the willingness to give up units of the other good declines.

Marginal rate of substitution
MRS_xy is the rate at which a consumer is willing to give up units of Y to obtain one more unit of X while keeping utility unchanged. It equals the absolute slope of the IC. Diminishing MRS means consumers prefer balanced bundles rather than extremes, producing convex IC shapes.

Budget constraint and consumer equilibrium
The budget line is P_x X + P_y Y = M and its slope is -P_x/P_y. Consumer equilibrium occurs where the highest reachable indifference curve is tangent to the budget line: MRS_xy = P_x/P_y. At tangency the subjective trade-off (MRS) equals the market trade-off (price ratio), so the consumer cannot reallocate spending to increase utility.

Special cases
Perfect substitutes have linear ICs (constant MRS); the consumer chooses the cheaper per-unit utility good. Perfect complements (L-shaped ICs) require fixed proportions of consumption, and the optimum occurs at the kink where the proportion matches the budget. These special cases illustrate how preferences shape demand elasticity and responsiveness to price changes.

Income and substitution effects with ICs
When price of a good changes, total change in quantity demanded is decomposed into substitution effect (movement along an indifference curve to a compensated budget line) and income effect (shift to new indifference curve due to change in real purchasing power). Hicksian (compensated) and Slutsky decompositions differ in the compensation method but both clarify how price changes affect demand.

Applications
Indifference curve analysis helps derive individual and market demand curves, evaluate welfare effects of price policies, and analyse consumer choices under constraints. It provides a flexible and rigorous framework for understanding how preferences and budget limits determine consumption patterns.

Production function in the short run
The production function expresses the maximum output obtainable from given quantities of inputs. In the short run at least one input (commonly capital) is fixed while other inputs (labour, raw materials) vary. For example, with fixed plant size K̅ and varying labour L, output is Q = f(L; K̅). The short-run focus allows analysis of how variable inputs change output given fixed capacity.

Total, marginal and average products
Total product (TP) is the total output produced with given inputs. Marginal product of labour (MP_L) is the extra output from adding one more worker: MP_L = ΔTP/ΔL. Average product (AP_L) is output per worker: AP_L = TP/L. Typically MP rises initially (specialisation and division of labour) then falls due to diminishing marginal returns as fixed factors bind more tightly.

Law of diminishing marginal returns
As more units of a variable input are added to fixed inputs, holding technology constant, the marginal product eventually declines. This law explains the upward-then-downward shape of many short-run marginal product curves and underpins the rising marginal cost behavior seen in cost analysis.

Short-run cost components
Total cost (TC) equals total fixed cost (TFC, incurred even at zero output) plus total variable cost (TVC, rising with output): TC = TFC + TVC. Average cost (AC) = TC/Q; average fixed cost (AFC) = TFC/Q; average variable cost (AVC) = TVC/Q. Marginal cost (MC) = ΔTC/ΔQ and because TFC does not change with Q, MC = ΔTVC/ΔQ. Understanding how these costs behave as output changes is key for firm decisions.

Relations between product and cost curves
MP and MC are inversely related: when MP is rising, MC falls; when MP falls, MC rises. Consequently the MC curve typically falls initially and then rises, intersecting AVC and AC at their minimum points. AFC declines continuously with output because fixed costs are spread over more units, pulling AC down at low outputs before MC’s rise pushes AC up.

Short-run supply and firm behaviour
In perfect competition, a firm’s short-run supply curve is the portion of its MC curve above AVC. The profit-maximising output satisfies MR = MC (with MR = market price P for a price-taking firm). If price falls below AVC, the firm should shut down temporarily because it cannot cover variable costs.

Applications and numerical practice
Students should practise constructing product schedules, computing MP and AP, deriving TVC from labour costs and plotting cost curves. Numerical problems often give TP schedules or cost tables; use them to calculate MC, AVC, AC and determine profit-maximising output under given market prices.

Long-run perspective
In the long run all inputs are variable and firms can adjust plant size, adopt new technologies, or change the scale of operations. Long-run analysis focuses on how output changes when all inputs are varied together and how costs behave when firms choose the optimal combination of inputs for each output level.

Returns to scale defined
Returns to scale describe how output responds to proportional changes in all inputs. If doubling all inputs more than doubles output, the production function exhibits increasing returns to scale (IRS). If output doubles exactly, it is constant returns to scale (CRS). If output less than doubles, it is decreasing returns to scale (DRS). Returns to scale are long-run technical properties of the production process and differ from short-run diminishing marginal returns.

Causes of different returns
IRS often arises due to specialisation, division of labour, and indivisibilities in capital where larger scale allows cost savings. DRS can result from managerial inefficiencies, coordination problems, or congestion. CRS implies proportional scaling without significant efficiency gains or losses.

Long-run cost implications
The long-run average cost (LRAC) curve represents minimum average cost achievable at each output when the firm can adjust all inputs optimally. LRAC is the lower envelope of a family of short-run average cost (SRAC) curves corresponding to different plant sizes. When LRAC falls with output, economies of scale exist; when LRAC rises, diseconomies of scale dominate.

Economies and diseconomies of scale
Economies of scale include technical economies (better machines), managerial economies (specialised management), financial economies (cheaper finance), marketing economies (bulk advertising) and purchasing economies (bulk buying). Diseconomies may stem from bureaucratic complexity, communication issues, and coordination costs as size increases. Identifying which forces operate helps firms decide optimal scale.

Planning and expansion path
Using isoquant and isocost analysis, firms determine least-cost input combinations for each output. The expansion path traces these cost-minimising input choices as output expands, and maps onto the LRAC curve. Strategic decisions—whether to expand plant size or remain small—depend on expected demand and position on the LRAC curve.

Industry implications
Industries with strong economies of scale may be dominated by few large firms or a natural monopoly. Industries with constant returns can sustain many small firms under competition. Understanding returns to scale helps explain market structure, entry barriers and policies related to mergers and industry regulation.

Long-run cost structure
In the long run, firms can vary all inputs and select the plant or technology that minimises costs for any desired output level. This flexibility means long-run cost curves reflect opportunities for substituting inputs and exploiting scale economies, yielding possibly different shapes than short-run cost curves. The LRAC is constructed as the lower envelope of SRACs for different plant sizes, showing the least average cost attainable for each output level.

Isoquant-isocost analysis
The isoquant represents all input combinations yielding a given output; the isocost line represents all input combinations that cost the same given factor prices. Minimising cost for a given output requires tangency between an isoquant and an isocost: MRTS (marginal rate of technical substitution) equals the ratio of input prices. Repeating this minimisation for various outputs traces the expansion path and LRAC.

Revenue in long-run context
Total revenue (TR) equals price times quantity. Average revenue (AR) = TR/Q and marginal revenue (MR) = ΔTR/ΔQ. For price-taking firms AR and MR equal market price. For firms with market power AR declines with output and MR lies below AR. In the long run firms choose output where MR = MC and select scale to maximise profit given expected market conditions.

Long-run equilibrium and normal profit
In perfect competition free entry and exit ensure long-run economic profit is zero: price equals minimum long-run average cost (P = min LRAC). Firms earn normal profit—compensation for entrepreneurship and opportunity costs—but no economic profit. Entry and exit adjust industry supply until this condition is satisfied.

Strategic implications
Firms planning long-run expansion must consider expected demand growth, technological change and factor price trends. Investment decisions weigh present value of future returns against cost of capital. When firms face declining LRAC over the relevant demand range, larger scale may be desirable; otherwise smaller specialised firms might be more efficient.

Policy and market structure
Industries with large scale economies relative to market demand may naturally lead to monopoly or oligopoly; regulators consider average cost pricing or public provision to prevent abuse of market power. Long-run analysis informs merger policy, industrial strategy and infrastructure investments.

Defining characteristics
Perfect competition is a theoretical market structure featuring many small firms, homogeneous products, perfect information, no transaction costs, and free entry and exit. Because each firm is tiny relative to the market, it is a price taker: it accepts the market price and cannot influence it. Perfect competition provides a benchmark for efficiency analysis.

Firm revenue under perfect competition
A competitive firm faces a horizontal demand curve at market price. Average revenue (AR) equals price (AR = P) and marginal revenue (MR) equals AR: MR = AR = P. Thus the revenue side is simple and the firm's quantity decision depends on its cost structure.

Profit maximisation in the short run
A competitive firm maximises profit by producing where MR = MC, i.e., P = MC. If at this output price exceeds average cost, the firm makes positive economic profit; if price is below average cost but above AVC, it incurs losses but continues producing to cover some fixed costs. If price falls below AVC, the firm should shut down in the short run because it cannot cover variable costs.

Short-run supply curve
The firm's short-run supply curve is the portion of its MC curve that lies above AVC. At prices below minimum AVC quantity supplied is zero. Aggregating individual supply curves horizontally yields market supply, which together with market demand determines short-run market price.

Long-run adjustments and equilibrium
With free entry and exit, short-run economic profits attract new firms and losses drive exit. This entry/exit process shifts market supply until firms earn zero economic profit in long run: P = min LRAC = MC at output where AC is minimised. In the long run firms produce at efficient scale, and the market price reflects true long-run costs.

Efficiency properties
Perfect competition achieves allocative efficiency (P = MC) and productive efficiency in the long run (firms produce at min AC). Consumer surplus is maximised subject to production possibilities. These properties make perfect competition a useful normative benchmark though real markets often deviate due to product differentiation, scale economies, or information imperfections.

Applications and limitations
Some agricultural and commodity markets approximate competitive conditions, but many real markets have product differentiation, scale economies or sticky prices. Nonetheless, analysis of perfect competition helps evaluate welfare losses when markets depart from this benchmark because of taxes, subsidies or market power.

Nature and sources of monopoly power
Monopoly exists when a single firm supplies the entire market and faces the market demand curve. Barriers to entry sustain monopolies: legal protections (patents, licenses), control of essential resources, network effects, or strong economies of scale that make a single large firm most efficient (natural monopoly). Monopolists have market power to influence price and output.

Revenue characteristics
Because the monopolist faces a downward-sloping demand curve, average revenue (AR = P) falls as output rises and marginal revenue (MR) lies below AR. For a linear demand P = a - bQ, total revenue TR = aQ - bQ^2 and MR = a - 2bQ. The gap between AR and MR reflects the fact that to sell additional output the monopolist must lower price on all units if it charges a single price.

Profit maximisation
Monopolist maximises profit by choosing output where MR = MC and then charging the highest price consumers will pay for that output from the demand curve. This yields P > MC and typically P > AC, allowing the monopolist to earn positive economic profit in the long run due to entry barriers. The monopolist’s output is lower and price higher than under perfect competition.

Welfare consequences
Monopoly leads to allocative inefficiency because output is restricted below the competitive level where P = MC. The resulting deadweight loss represents mutually beneficial trades that do not occur. Consumer surplus falls and producer surplus rises; total social welfare declines. Society faces a trade-off if monopoly allows cost-saving innovations or sustainability of production that competitive entry might not permit.

Price discrimination and its effects
Monopolists may practise price discrimination—charging different prices to different buyers or quantities—to capture more consumer surplus. First-degree discrimination extracts full willingness to pay; second-degree uses menus or quantity discounts; third-degree charges different prices to identifiable segments. Price discrimination can increase output and firm profit while redistributing surplus; sometimes it improves welfare if it brings previously excluded consumers into the market.

Regulation and natural monopolies
Natural monopolies with declining LRAC can be regulated through average-cost pricing (P = AC) or marginal-cost pricing with subsidy (P = MC plus subsidy) to improve welfare. Competition policy, price-cap regulation and public ownership are tools to control monopoly abuses while preserving scale economies where present.

Monopolistic competition: features and outcomes
Monopolistic competition describes markets with many firms selling differentiated products, free entry and exit, and some degree of price-setting power by each firm. Differentiation can be through quality, brand, location or features. Each firm faces a downward-sloping demand curve for its unique product, and uses advertising and non-price competition to attract customers.

Short-run and long-run equilibrium
In the short run, a firm may earn positive or negative economic profits depending on demand and cost conditions. Free entry erodes positive profits: new entrants offer close substitutes, shifting demand left for incumbents until economic profit is driven to zero in the long run. Long-run equilibrium occurs where demand (AR) is tangent to the AC curve, so price exceeds marginal cost (P > MC) and firms operate with excess capacity—producing below the minimum point of AC.

Implications for welfare
Monopolistic competition provides product variety and consumer choice but is inefficient in allocation (P > MC) and productive efficiency (firms do not produce at minimum AC). Consumers gain from variety but pay higher prices relative to marginal cost. Advertising and branding can increase demand but add to costs, affecting long-run prices and welfare balance.

Oligopoly: strategic interdependence
Oligopoly markets have a few large firms whose actions influence one another. Strategic considerations matter: firms anticipate rivals’ responses when choosing price, quantity, advertising or capacity. This leads to game-theoretic models such as Cournot (quantity competition), Bertrand (price competition), and Stackelberg (leader-follower). Outcomes vary: Cournot often yields intermediate prices between monopoly and competition; Bertrand with homogeneous products and constant marginal cost leads to competitive pricing (P = MC).

Collusion and competition policy
Oligopolists may collude to achieve monopoly-like outcomes, forming cartels that restrict output and share markets. Collusion raises prices and reduces welfare; it is often illegal. Tacit collusion (price leadership) can be harder to detect. Competition policy and antitrust laws aim to prevent anti-competitive agreements and promote contestability.

Non-price competition and role of advertising
In both market forms firms engage in non-price strategies: product differentiation, quality improvements, branding, and advertising. These increase consumer information and perceived differences but also raise costs. Advertising can shift demand curves and make demand less price-elastic, affecting market power and pricing strategies.

What is market failure?
Market failure occurs when the free-market outcome is not socially optimal—when markets fail to allocate resources efficiently or fairly. Common causes include externalities (spillovers), public goods, asymmetric information, market power and missing markets. Identifying the source of failure helps design appropriate policy responses.

Externalities explained
Externalities are costs or benefits experienced by third parties not reflected in market transactions. Negative externalities (pollution, noise) cause overproduction relative to the social optimum because private marginal cost (PMC) is lower than social marginal cost (SMC). Positive externalities (education, vaccinations) cause underproduction because private marginal benefit is less than social marginal benefit. Policy responses include taxes or regulations for negative externalities and subsidies or public provision for positive ones.

Coase theorem and property rights
The Coase theorem states that if property rights are well-defined and transaction costs are zero, private bargaining can lead to efficient outcomes regardless of initial rights allocation. In practice transaction costs and bargaining difficulties often limit this solution, so policy instruments may be necessary.

Public goods and free riding
Public goods are non-excludable and non-rivalrous: one person's consumption does not reduce availability for others and it is hard to exclude non-payers. Such goods—national defence, street lighting—are underprovided by markets because individuals free-ride, relying on others to pay. Government provision funded by taxation or club provision with exclusion mechanisms are common remedies.

Common property and tragedy of the commons
Common-property resources (open-access fisheries, grazing land) are rivalrous but non-excludable, leading to overuse and depletion—the tragedy of the commons. Solutions include regulation, use rights, privatization, or community management schemes that limit access and internalise costs.

Asymmetric information
When one party has more information than another, markets may fail. Adverse selection (hidden characteristics) can cause market collapse, as in insurance markets; moral hazard (hidden actions) can cause excessive risk-taking after contracts. Remedies include signalling (education credentials), screening (tests), warranties, and regulation to improve transparency.

Policy trade-offs and evaluation
Interventions to correct market failures must consider costs, incentives and feasibility. Taxes and subsidies change behaviour but incur administrative costs and may create distortions. Regulation can reduce externalities but may impose compliance burdens. The best policy balances efficiency, equity and political feasibility while minimising unintended consequences.

Derived demand for factors
Demand for factors like labour and capital is derived from the demand for the final product. Firms hire a factor up to the point where its value of marginal product (VMP) equals its price (factor cost). Under perfect competition in product market, value of marginal product equals marginal product times output price: VMP_L = MP_L × P. Firms hire labour until MRP (marginal revenue product) equals wage.

Labour market basics
Labour supply depends on wage rates, preferences between leisure and consumption, population size and demographics. In a competitive labour market, equilibrium wage equates labour supply and demand. Labour markets are affected by mobility, skill levels, unions, minimum wage laws and social norms. Wage differentials across occupations arise from differences in skills, working conditions, location and labour market imperfections.

Monopsony and wage setting
A monopsony is a single buyer of labour in a market. In this case the firm faces the upward-sloping labour supply curve and sets wages below marginal revenue product by choosing employment where MRP = MFC (marginal factor cost), hiring fewer workers and paying lower wages than in competitive markets. Minimum wage laws can raise wages and employment in monopsonistic markets in some circumstances.

Capital markets and interest rates
Demand for capital is based on expected returns relative to its rental price or interest rate. Investment decisions depend on expected marginal productivity, depreciation, and cost of finance. The loanable funds model shows saving supplies funds and investment demands them; equilibrium real interest rate clears the market. Policies affecting savings or investment tax incentives shift these curves and change equilibrium interest rates and investment.

Rent and land
Rent is payment to a factor in excess of its opportunity cost, often due to fixed supply. For land with fixed supply, rent is determined by demand. Differential rent arises from differences in fertility or location. Economic rent is a surplus payment because supply cannot increase to bid rent away.

Income distribution and policy
Factor market outcomes determine distribution of income among wages, interest, rent and profits. Policies such as minimum wages, progressive taxation, education and training programs influence earning capacity and distribution. Understanding factor markets is essential for designing policies that affect employment, growth and equity.

Taxes and their market effects
Taxes on goods, whether specific (per-unit) or ad valorem (percentage), alter relative prices and distort market outcomes. A tax on sellers shifts the supply curve upward by the tax amount; a tax on buyers shifts the demand curve downward effectively. The result is a higher price paid by buyers and a lower price received by sellers, with the difference equal to the tax. Quantity traded falls, and the government collects tax revenue equal to tax per unit times quantity after tax.

Tax incidence
Statutory incidence (who the tax is levied on) differs from economic incidence (who bears the burden). Incidence depends on elasticities: the side of the market (demand or supply) that is less price-elastic bears a larger share of the tax burden. For example, if demand is inelastic and supply elastic, consumers bear most of the tax burden.

Deadweight loss from taxes
Taxes create deadweight loss by preventing mutually beneficial trades. The magnitude of deadweight loss depends on the elasticities of demand and supply and the size of the tax: more elastic curves and larger taxes produce larger efficiency losses. Governments must weigh revenue gains against the efficiency costs when designing taxes.

Subsidies and distortions
Subsidies lower producers’ effective costs or raise consumers’ purchasing power, shifting supply right or demand right. While subsidies can correct positive externalities or support disadvantaged groups, they also create fiscal cost and can lead to overproduction, market distortions and misallocation of resources if poorly targeted.

Price controls: ceilings and floors
Price ceilings (maximum prices) set below equilibrium cause shortages and non-price rationing mechanisms (queues, black markets). Price floors (minimum prices) above equilibrium cause surpluses and may require government purchases or disposal programs. Both controls disrupt market signals and often reduce quality, investment and proper allocation of resources.

Policy design and corrective taxes
Corrective or Pigovian taxes aim to internalise external costs by setting the tax equal to the marginal external cost, restoring efficiency. Subsidies can be used to encourage activities with positive externalities. Policy effectiveness depends on accurate measurement of externalities, administrative capacity and minimizing unintended consequences such as evasion or rent-seeking.

Practical evaluation
When evaluating interventions consider distributional effects, revenue or fiscal costs, administrative feasibility and behavioural responses. Use elasticity estimates and welfare triangle calculations to quantify impacts and guide policy choices.

Measuring welfare in markets
Welfare economics uses consumer surplus and producer surplus to measure gains from trade. Consumer surplus is the area between the demand curve and the market price, representing the difference between willingness to pay and actual payment. Producer surplus is the area between market price and supply (or marginal cost), representing the difference between price received and minimum acceptable price. Total surplus sums both and indicates overall economic welfare under given market conditions.

Efficiency of competitive equilibrium
In perfect competition the market equilibrium maximises total surplus because price equals marginal cost (P = MC), so each unit produced provides benefit at least as large as its cost. This allocative efficiency means no further reallocation could make someone better off without making someone else worse off. Competitive markets therefore achieve Pareto efficiency under standard assumptions (no externalities, complete markets).

Effects of distortions
Market distortions like taxes, subsidies, monopolies and externalities alter surplus distribution and reduce total surplus. A per-unit tax creates a wedge between price paid and price received, shrinking consumer and producer surplus and generating deadweight loss — the triangular area of lost trades that would have been mutually beneficial absent the tax. Monopoly restricts output compared to competition, creating deadweight loss and transferring some consumer surplus to producer profit.

Compensating and equivalent variation
To measure welfare changes in monetary terms when prices change, economists use compensating variation (how much income would compensate the consumer after a price change to restore original utility) and equivalent variation (how much income change before the price change would produce the same utility change). These concepts help evaluate distributional consequences and policy impacts more precisely than crude surplus changes alone.

Distribution vs efficiency
Maximising total surplus does not address equity. Policies that increase total surplus may worsen income distribution. Welfare analysis therefore often combines efficiency calculations with normative judgments or redistributive policies to achieve social objectives while minimising efficiency loss.

Applications in policy evaluation
Cost-benefit analysis uses surplus measures to compare policies by estimating changes in consumer and producer surplus, government revenues and external costs or benefits. Estimating these requires demand and supply elasticity data, valuation of non-market goods and careful treatment of distributional weights when social welfare prioritises equity.

Partial vs general equilibrium
Partial equilibrium examines a single market in isolation, holding other markets constant. General equilibrium studies many markets simultaneously and how they interact. General equilibrium is important because changes in one market affect others; for instance, a subsidy in agriculture influences labour and capital markets, prices of related goods, and income distribution economy-wide.

Edgeworth box and exchange
The Edgeworth box graphically represents allocations of two goods between two consumers. Each point in the box shows how total endowments are divided. Indifference curves of both consumers inside the box reveal possible trades. The contract curve is the locus of Pareto-efficient allocations where indifference curves are tangent. Voluntary trade moves allocations from initial endowment toward the contract curve, increasing welfare for both parties until no mutually beneficial trades remain.

First welfare theorem
The first welfare theorem states that, under assumptions such as perfect competition, complete markets, no externalities and convex preferences, any competitive equilibrium allocation is Pareto efficient. This formalises the idea that competitive markets can coordinate decentralized decisions to achieve an efficient allocation of resources.

Second welfare theorem
The second welfare theorem states that any Pareto-efficient allocation can be achieved as a competitive equilibrium after appropriate redistribution of initial endowments (lump-sum transfers), assuming convexity of production and preferences. This separates efficiency (achieved by markets) from equity (achieved by redistribution), suggesting policy can target distribution without sacrificing efficiency if redistribution is done via non-distortionary lump-sum transfers.

Limitations and realistic failures
Welfare theorems rely on strong assumptions that often fail: externalities, public goods, incomplete markets, non-convexities, and information imperfections. When these hold, market equilibria may be inefficient and policy interventions might improve welfare. General equilibrium models can be extended to include these features to evaluate policy trade-offs.

Practical implications
General equilibrium analysis helps assess economy-wide effects of policies such as tariffs, taxation and subsidies. It informs macroeconomic policy by accounting for inter-market feedbacks and provides theoretical foundations for understanding when markets deliver good outcomes and when coordinated interventions are necessary.