Demand
Introduced| English | Meaning |
|---|---|
| law of demand/lɔː ɒv dɪˈmænd/ | The tendency for quantity demanded to fall as price rises, with other relevant factors held constant. |
| demand/dɪˈmænd/ | The quantity of a good or service that buyers are willing and able to purchase at different prices over a period. |
| quantity demanded/ˈkwɒntɪti dɪˈmændɪd/ | The amount buyers are willing and able to purchase at a particular price over a specified period. |
| normal goods/ˈnɔːml ɡʊdz/ | A good for which demand increases as consumer income rises, with other factors held constant. |
| substitutes/ˈsʌbstɪtjuːts/ | Goods or services that can be used in place of each other. |
| complements/ˈkɒmplɪmənts/ | Goods or services typically used together, so demand for one is linked to the use of the other. |
Why queues form on Black Friday
- Slash a price and crowds appear; raise it and they melt away. That predictable response is the law of demand 需求定律.
- Demand 需求 is the foundation of every market — understanding it lets you predict how buyers react to price, income and fashion.
The law of demand says that, other things equal, as price rises quantity demanded:
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Higher price → lower quantity demanded; the demand curve slopes downward.
The law of demand
- Demand is the quantity buyers are willing and able to buy at each price.
- The law of demand: as price rises, quantity demanded 需求量 falls (and vice versa) — so the demand curve slopes downward.
Higher price → lower quantity demanded (move along D₁); a rise in demand shifts the whole curve right to D₂.
Demand & supply
Demand slopes down — a lower price, more is wanted.
A rise in consumer income causes:
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Only the good's own price moves you along the curve; income shifts the whole curve.
A change in the good's own price causes a movement along the demand curve, not a shift.
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Own-price → movement along; other factors → shift.
Movement vs shift
- A change in price → a movement along the curve (a change in quantity demanded).
- A change in anything else → a shift of the whole curve (a change in demand).
This distinction wins marks. Only the good's own price moves you along the curve. Income, tastes, or other prices shift it. Mixing these up is the classic exam error.
Match each change to its effect on the demand for coffee.
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Substitutes and income raise demand; a dearer complement lowers it; tastes shift it too.
Two goods used together (like cars and petrol) are called ______.
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A rise in the price of one reduces demand for the other.
What shifts demand
- Income (more income → more demand for normal goods 正常品),
- Tastes/fashion (a trend raises demand),
- Substitutes 替代品 (a rival's price rises → demand for this good rises),
- Complements 互补品 (a partner good's price rises → demand for this falls),
- Population and expectations.
You've got it
- law of demand: price up → quantity demanded down (downward curve)
- own-price change = movement along; anything else = shift of the curve
- demand shifts with income, tastes, substitutes, complements, population