👆 Movements Along the Demand Curve
The Rule: A movement along the demand curve happens when the price of the good itself changes. Nothing else. The curve stays in the same position — you just move to a different point on it.
How it works
- Price RISES → move UP and LEFT along the curve → quantity demanded FALLS
- Price FALLS → move DOWN and RIGHT along the curve → quantity demanded RISES
The demand curve itself does not move to a new position. You simply travel along the existing curve from one price-quantity point to another.
The correct term is a change in quantity demanded (not a 'change in demand'). This wording matters for exam marks!
↔️ Shifts of the Demand Curve
The Rule: A shift of the demand curve happens when a non-price factor changes. The entire curve moves to a new position — left or right.
Right shift (increase in demand)
- The whole curve moves to the RIGHT
- At every price, consumers now want to buy MORE
- Caused by: higher income (normal good), rise in price of a substitute, increase in population, positive change in tastes
Left shift (decrease in demand)
- The whole curve moves to the LEFT
- At every price, consumers now want to buy LESS
- Caused by: lower income (normal good), fall in price of a substitute, decrease in population, negative change in tastes
The correct term is a change in demand (or 'increase/decrease in demand'). This means the whole curve has shifted.
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🎯 Telling Movements and Shifts Apart
This is one of the most frequently tested skills in IB Economics. Examiners use it to check whether you really understand demand, and getting the terminology wrong will cost you marks.
The simple rule
- Price of the good CHANGES → MOVEMENT along the curve
- ANYTHING ELSE changes (income, tastes, related goods, etc.) → SHIFT of the curve
The terminology trap
Examiners look for precise language. Using the wrong phrase can cost marks even if your diagram is correct.
- 'Increase in demand' = curve shifts RIGHT (more demanded at every price)
- 'Increase in quantity demanded' = movement DOWN-RIGHT along the curve (because price fell)
- These are NOT the same thing — mixing them up is the most common exam mistake
A past paper asked: 'Explain why an increase in demand raises price, while an increase in price reduces quantity demanded.' The answer requires you to explain that an increase in demand (shift right) raises equilibrium price, while a higher price causes a movement along the curve to a lower quantity demanded. Two different mechanisms!
Before drawing any diagram, ask yourself: 'Did the PRICE of this good change, or did something ELSE change?' That tells you whether to show a movement or a shift.