Every microeconomics topic answers the same underlying question: who is the decision-maker, what constrains them, what changes, and what new choice or market outcome follows? Wherever a diagram is involved, the discipline that separates a strong answer from a weak one is distinguishing a movement along a curve (caused only by a change in that curve’s own price variable) from a shift of the whole curve (caused by anything else), always under a stated ceteris-paribus assumption (everything else held constant).
A. Consumer Behaviour
Consumer theory asks how a person with limited income chooses among goods and services to obtain the greatest possible satisfaction. Two complementary tools are used: utility analysis and indifference-curve analysis. In utility analysis, marginal utility is the extra satisfaction from one more unit of a good, and the law of diminishing marginal utility says this extra satisfaction typically falls as consumption of the good increases. In indifference-curve analysis, a consumer’s preferences are represented by indifference curves (combinations of goods giving equal satisfaction), while a budget line represents what the consumer can actually afford given income and prices. Consumer equilibrium occurs where the consumer reaches the highest attainable indifference curve given the budget line — geometrically, where the budget line is tangent to an indifference curve, meaning the marginal rate of substitution (how much of one good the consumer is willing to trade for another) equals the price ratio between the two goods. Example: with income of Rs 1,000, a consumer cannot buy unlimited quantities of every good; if the price of one good rises, the set of affordable combinations shrinks on that side, which can shift the final chosen combination even if income and other prices stay the same.
B. Market Demand and Supply, and Elasticity
Demand shows how much buyers are willing and able to buy at different prices; supply shows how much sellers are willing and able to sell at different prices. Market equilibrium is the price and quantity at which quantity demanded equals quantity supplied. A movement along a demand or supply curve is caused only by a change in the good’s own price; a shift of the entire curve is caused by any other determinant, such as income, tastes, the price of related goods, input costs, technology, or expectations. Example: if new technology lowers production cost, the supply curve shifts right, producing a lower equilibrium price and a higher equilibrium quantity, other things unchanged. Confusing these two — treating a shift as if it were a movement, or vice versa — is the single most common error in this whole paper.
Elasticity measures how strongly quantity responds to a change in price, income, or another determinant. Price elasticity of demand compares the percentage change in quantity demanded with the percentage change in price; demand is called elastic when this ratio exceeds one, inelastic when it is below one, and unit-elastic when it equals one. Example: if price rises 10% and quantity demanded falls 20%, the absolute price elasticity is 2, so demand is elastic over that price range. Income elasticity and cross-price elasticity extend the same percentage-responsiveness logic to classify goods (normal versus inferior, substitutes versus complements) rather than just describing the price-quantity relationship. Elasticity also determines how a price change affects total revenue: when demand is elastic, a price cut increases total revenue (the percentage rise in quantity outweighs the percentage fall in price); when demand is inelastic, a price cut decreases total revenue. Supply elasticity depends strongly on time: supply tends to be more elastic (responsive) the longer the time period allowed for producers to adjust their production.
C. Static, Comparative Static, and General Equilibrium Analysis
Static analysis studies an equilibrium at a single point in time or under one given set of conditions. Comparative statics compares one equilibrium against another after some condition has changed, typically telling us the direction and, often, the size of the resulting change — without necessarily modeling the exact time-path the market follows while adjusting from the old equilibrium to the new one. Example: comparing the market equilibrium before and after a rise in consumer income shows the new price and quantity directly, without describing every intermediate step of the adjustment process.
Partial equilibrium studies one market largely in isolation, which is simpler and perfectly adequate when spillover effects into other markets are small. General equilibrium instead studies many interconnected markets together, recognizing that a change in one market can ripple into others’ income, costs, demand, and prices. Example: a tax on fuel affects the fuel market directly (a partial-equilibrium view), but it can also raise transport costs across the economy and thereby influence many other markets at once (a general-equilibrium view) — the same event, analyzed at two different levels of scope.
D. Theory of the Firm and Producer’s Equilibrium
The theory of the firm explains how a producer chooses output, inputs, and production methods while facing given costs, technology, and market conditions. Core tools: the production function relates inputs to output; total, average, and marginal product describe output as one input (commonly labour) is varied while others (commonly capital) are held fixed in the short run; total, average, and marginal cost mirror this on the cost side; and revenue curves depend on the market structure the firm sells into. Example: a bakery may add more workers while its oven size stays fixed — output typically rises quickly at first, but as the fixed oven becomes crowded, each additional worker adds a progressively smaller increment to output. This pattern is the law of diminishing marginal returns, and it is the microeconomic foundation for the shape of short-run cost curves.
Market structure changes how much pricing power a firm has: perfect competition (many firms, identical product, no individual pricing power), monopoly (a single seller with significant pricing power), monopolistic competition (many firms, differentiated products, some pricing power), and oligopoly (few firms, strategic interdependence between rivals) each imply a different relationship between price, output, and profit.
Producer’s equilibrium is the output or input combination at which the firm has no incentive to change its decision, given its objective and constraints. For a profit-maximizing firm choosing output, the standard condition is that marginal revenue equals marginal cost: a competitive firm compares the extra revenue from producing one more unit against the extra cost of producing it, and increases output whenever extra revenue exceeds extra cost, stopping exactly where the two are equal. For choosing the least-cost combination of inputs to produce a given output, isoquant (equal-output) and isocost (equal-cost) analysis plays the same equilibrium role that indifference curves and budget lines played for the consumer in Section A — the logic of tangency-based equilibrium repeats across the whole subject.
E. Pricing of Factors of Production
The factors of production — labour, land, capital, and entrepreneurship — receive payments conventionally described as wages, rent, interest, and profit respectively. Factor demand is generally a derived demand: firms do not want labour or capital for their own sake but because they help produce a final good or service that is itself demanded, so factor demand ultimately traces back to demand for the final product. Marginal productivity theory captures this at a basic level: a factor that adds more value to output tends to generate stronger demand for itself. Example: a worker who adds more value to output can create stronger demand for labour, but the wage actually paid also depends on labour supply conditions, bargaining power, institutions such as minimum-wage laws or unions, and the overall market structure — productivity alone does not fully determine the wage.
Microeconomics key takeaways: every topic reduces to decision-maker, constraint, changing variable, and resulting outcome. Consumer and producer equilibrium share the same tangency logic (marginal rate of substitution equals price ratio for the consumer; least-cost input combination for the firm). A movement along a curve is never the same thing as a shift of the curve, and every diagram-based answer should state its ceteris-paribus assumption explicitly. Elasticity determines the direction in which a price change moves total revenue. Partial equilibrium is a simplification of general equilibrium, valid when spillovers to other markets are small. Factor prices depend on marginal productivity, but also on supply-side and institutional conditions that productivity alone does not capture.