What it covers: The conceptual foundation of macroeconomics — scarcity, the PPC, comparative advantage, and supply and demand.
Exam weight: About 5–10% of the AP Macroeconomics exam.
The big question: Given that resources are scarce, how do individuals, firms, and economies decide what to produce, and how do markets coordinate those decisions through prices?
Big Ideas covered: Scarcity, Markets, and Macroeconomic Models.
Key topics at a glance
Economic Thinking & Models
Scarcity forces choice, and every choice has an opportunity cost. Economists use ceteris paribus to build simplified models that isolate one variable at a time.
Economic Systems
Every economy answers what, how, and for whom to produce. Command economies use central planning; market economies use decentralized price signals.
Production Possibilities Curve
Shows max output combos with given resources. Points inside = inefficiency. Points outside = unattainable (without growth). The curve's bowed shape shows increasing opportunity cost.
Comparative Advantage & Trade
Absolute advantage: producing more with the same resources. Comparative advantage: lower opportunity cost — this is what should drive specialization and trade.
Demand
Law of demand: price ↑, quantity demanded ↓. A movement along the curve comes from a price change; a shift comes from income, tastes, related-good prices, expectations, or number of buyers.
Supply
Law of supply: price ↑, quantity supplied ↑. Shifts come from input costs, technology, related-good prices, expectations, number of sellers, or government policy.
Use the shift-the-curve, find-the-new-intersection method. Demand and supply shifting in the same or opposite directions changes price and quantity in predictable ways.
The key terms you must know
Scarcity — limited resources relative to unlimited wants; the root of every economic decision.
Opportunity cost — the value of the next-best alternative given up by a choice.
Production possibilities curve — graph of maximum attainable output combinations of two goods.
Absolute vs. comparative advantage — producing more (absolute) vs. producing at lower opportunity cost (comparative). Comparative advantage drives trade.
Law of demand / Law of supply — the inverse price–quantity-demanded relationship and the direct price–quantity-supplied relationship.
Determinants of demand and supply — the non-price factors that shift entire curves.
Market equilibrium — the price and quantity where quantity supplied equals quantity demanded.
Surplus / shortage — the imbalance that occurs when price is above or below equilibrium, pushing price back toward balance.
Key themes to remember
Scarcity is the starting point of all economics. If resources weren't limited, there would be no opportunity cost and no need to choose.
Models trade realism for clarity. Ceteris paribus lets economists isolate one cause at a time — but real markets have many variables moving together.
Comparative advantage, not absolute advantage, drives specialization. A producer can be worse at everything in absolute terms and still have a comparative advantage in something.
Price changes cause movements; everything else causes shifts. This distinction is the single most-tested idea in Unit 1.
Markets self-correct. Surpluses and shortages aren't permanent — price adjustments push the market back to equilibrium.
Common exam traps
Don't confuse "demand" with "quantity demanded." Demand is the whole curve/relationship; quantity demanded is a single point on it.
A price change never shifts the demand or supply curve. It only causes a movement along the existing curve. Only non-price determinants shift the curve.
Increasing opportunity cost, not constant opportunity cost, is why the PPC bows outward. A straight-line PPC would imply resources are perfectly interchangeable, which is unrealistic.
Absolute advantage is not the same as comparative advantage. A country can have an absolute advantage in both goods and still only have a comparative advantage in one.
A surplus pushes price down; a shortage pushes price up — not the reverse. Double-check which side of equilibrium you're on before predicting price direction.
When both supply and demand shift, the effect on quantity or price can be ambiguous. Sketch both shifts and find the new intersection rather than assuming a direction.