Difficulty: Introductory | Prerequisites: None. This is first-week material.
This is the starting point for the entire course. Before you can talk about GDP, inflation, or trade policy, you need to understand why economics exists in the first place: resources are limited, people want more than they can have, and every choice has a cost. These three ideas (scarcity, rationality, opportunity cost) are the lens through which every later topic is viewed. If you missed the first few lectures, start here; everything else in Module 1 builds on this foundation.
Economics studies how people, firms and governments allocate scarce resources among unlimited wants. Every decision carries an opportunity cost: the value of the next-best option you gave up. Rational agents weigh costs against benefits and choose the option that makes them best off, given what they know at the time.
Economics
The study of how scarce resources are allocated among competing wants and needs. It is a quantitative social science built on measurement, models and cost-benefit analysis.
In simple terms, economics is about choices: who gets what, and what do they give up to get it.
Scarcity
The condition that arises because human wants are unlimited while the resources available to satisfy them are finite.
Think of it as the reason every choice has a cost. If everything were abundant, there would be nothing to study.
Opportunity cost
The value of the next-best alternative forgone when a decision is made.
In simple terms, it is the thing you gave up. If you chose to attend class instead of sleeping, the opportunity cost of attending class is the sleep you missed.
Rational decision making
The assumption that economic agents (individuals, firms, governments) weigh the costs and benefits of available options and select the one that maximises their well-being.
Think of it as: people do their best with what they know, even if they sometimes get it wrong because information is imperfect.
Self-interest
The motivation driving rational agents to choose actions that maximise their own benefits or utility.
This does not mean selfish. It means each agent pursues the outcome that is best for them, given their preferences.
Cost-benefit analysis
A framework for comparing the total expected costs against the total expected benefits of one or more actions, to determine the best course of action.
In simple terms, you list the pros and cons, attach values to them, and pick whichever option comes out ahead.
Utility
A measure of the satisfaction or benefit an individual derives from consuming a good or service, or from taking a particular action.
Think of it as a score for how happy or satisfied a choice makes you. Economists use it as shorthand for "what the person values."
Economics is the study of how scarce resources are allocated among competing wants
Classified as a quantitative social science: it relies on data, measurement and models
Cost-benefit analysis operates at every level:
Individuals choose based on utility (personal satisfaction)
Firms decide what to produce, how much, and at what price
Governments design policies that balance public costs and benefits
Core themes that run through every chapter: decision-making under scarcity, trade-offs, and resource allocation
Scarcity is the starting condition: wants are unlimited, resources are not
Because of scarcity, every society must answer three questions:
What to produce? Which goods and services get made?
How to produce? Which combination of resources and techniques?
For whom to produce? Who consumes the output?
Scarcity forces prioritisation. Without it, there would be no need for economics.
Economic models assume agents are rational and self-interested
Rational means: agents weigh costs against benefits and choose the option that maximises their utility
Self-interested means: agents pursue their own well-being (not necessarily selfish, just goal-oriented)
Key nuances:
Rationality does not require perfect information. People decide with what they know, and mistakes happen.
A rational choice can feel emotionally unsatisfying. The model cares about net benefit, not feelings.
This assumption underpins nearly every model you will encounter in this course.
Opportunity cost is the value of the next-best alternative you forgo when making a choice
It applies at every level:
Individual example: You skip sleep to attend an 8 a.m. lecture. The opportunity cost of the lecture is the rest you gave up.
Firm example: A factory uses its labour to produce chairs instead of tables. The opportunity cost is the profit from tables.
Society example: A government funds defence spending instead of healthcare. The opportunity cost is the healthcare it could have provided.
Opportunity cost is how economists quantify scarcity: it puts a number on what you sacrifice
It guides efficient decision-making: choose the option whose benefit exceeds its opportunity cost by the widest margin
Scarcity in action: During a drought, water is scarce. Governments must decide how to ration it: agriculture, households, or industry. The three fundamental questions play out in real time.
Opportunity cost in your own life: Choosing to attend university full-time means forgoing several years of full-time wages. The opportunity cost of a degree includes those lost earnings, not just tuition.
Rational self-interest in markets: Firms set prices to maximise profit; consumers comparison-shop to maximise value for money. Neither is doing anything exotic; they are just weighing costs against benefits.
Students often think opportunity cost means the monetary price of something. It does not. Opportunity cost is the value of what you gave up, which may have nothing to do with money (e.g. time, sleep, another experience).
Students often think "rational" means "emotionless" or "always correct." In economics, rational simply means the agent uses available information to pick the best option. Mistakes from incomplete information are still rational.
Students often confuse scarcity with shortage. Scarcity is a permanent condition (wants exceed resources). A shortage is a temporary market situation where quantity demanded exceeds quantity supplied at a given price.
Students sometimes think self-interest is the same as greed. Self-interest just means pursuing your own goals. A parent sacrificing sleep for their child is still acting in their self-interest if caring for the child is what they value most.
⚠️ Opportunity cost is one of the most frequently tested concepts in introductory economics. Be ready to calculate it and to identify it in word problems.
⚠️ The three fundamental questions (what, how, for whom) often appear as multiple-choice stems. Know them cold.
⚠️ Exam questions may test whether you can distinguish scarcity (permanent, universal) from shortage (temporary, market-specific).
⚠️ The rationality assumption is a building block. Later questions on consumer behaviour and firm behaviour assume you already understand it.
True or false: Scarcity only affects poor countries.
False. Scarcity is universal. Even the wealthiest nations face limited resources relative to unlimited wants.
Fill in the blank: The opportunity cost of a decision is the value of the ______ forgone.
next-best alternative
True or false: A rational decision always produces the best possible outcome.
False. Rational means choosing the best option given available information. Imperfect information can lead to suboptimal outcomes.
Fill in the blank: The three fundamental economic questions are what to produce, how to produce, and ______.
for whom to produce
True or false: Self-interest and greed are the same thing in economics.
False. Self-interest means pursuing your own goals, which can include altruistic preferences.
Q: Define economics in one sentence.
A: Economics is the study of how scarce resources are allocated among competing, unlimited wants and needs.
Q: A student has two hours free. She can study for her economics exam or work a shift that pays $30. She chooses to study. What is the opportunity cost of studying?
A: The opportunity cost is $30 (the wage she forfeited), plus any non-monetary benefits of working (experience, networking) that she gave up.
Q: Why does scarcity force societies to make choices?
A: Because resources are finite and wants are unlimited, a society cannot produce everything. It must decide what to produce, how to produce it, and who receives the output.
Q: Explain why a rational agent might still make a "bad" decision.
A: Rationality requires using available information to maximise benefit. If the information is incomplete or misleading, the agent can rationally choose an option that turns out poorly. The mistake reflects imperfect information, not irrationality.
Q: Is the opportunity cost of attending a free concert zero? Explain.
A: No. Even though the ticket costs nothing in money, the opportunity cost is whatever you would have done with that time instead (studying, working, resting). Opportunity cost includes non-monetary trade-offs.
Production Possibilities Frontier (PPF): The PPF is the graphical model that puts scarcity and opportunity cost on a diagram. Everything in these notes is the conceptual groundwork for reading and interpreting the PPF.
Comparative advantage and trade: Opportunity cost is the basis of comparative advantage. The country (or person) with the lower opportunity cost of producing a good has the comparative advantage, which is why trade benefits both parties.
Consumer and firm behaviour (later in the course): The rationality and self-interest assumptions carry forward. Consumer demand theory assumes utility maximisation; firm supply theory assumes profit maximisation. Both are extensions of rational choice.
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