š What Shifts the Supply Curve?
The Core Idea: A change in the good's own price causes a movement ALONG the supply curve. But a change in any non-price factor shifts the entire supply curve left or right.
Key determinants of supply
The main factors that can shift the supply curve are:
- Costs of production (wages, raw materials, energy, rent)
- Technology and innovation
- Government policy (taxes, subsidies, regulations)
- Number of firms in the market
- Expectations about future prices
- Weather and natural conditions (especially for agriculture)
Right shift vs left shift
- Right shift (Sā ā Sā) = INCREASE in supply ā more is supplied at every price
- Usually caused by lower costs, better technology, subsidies, or more firms
- Left shift (Sā ā Sā) = DECREASE in supply ā less is supplied at every price
- Usually caused by higher costs, taxes, regulations, or fewer firms
A helpful rule: anything that makes production CHEAPER shifts supply RIGHT (firms can produce more at every price). Anything that makes production MORE EXPENSIVE shifts supply LEFT.
š” The Main Supply Shifters
Costs of production
Costs of production are the single biggest factor affecting supply. When costs change, supply shifts.
- Wages rise ā costs increase ā supply shifts LEFT (firms produce less at each price)
- Raw material prices fall ā costs decrease ā supply shifts RIGHT
- Energy or fuel prices rise ā costs increase ā supply shifts LEFT
- Rent increases ā costs increase ā supply shifts LEFT
Technology
Better technology allows firms to produce the same quantity at lower cost, or more quantity at the same cost. Technology improvements almost always shift supply to the RIGHT.
- Automation lowers labour costs ā supply shifts right
- Better machinery increases output per worker ā supply shifts right
- Digital tools reduce waste and improve efficiency ā supply shifts right
Government policy
- Indirect taxes (e.g. on tobacco, alcohol) raise costs ā supply shifts LEFT
- Subsidies (e.g. for renewable energy) reduce costs ā supply shifts RIGHT
- Regulations (e.g. pollution standards) raise costs ā supply shifts LEFT
- Deregulation removes cost burdens ā supply shifts RIGHT
Past papers often feature energy price rises that shift supply left. When fuel or electricity costs increase, production becomes more expensive across many industries, reducing supply.
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š More Factors That Shift Supply
Number of firms
If new firms enter the market, market supply increases (shifts right) because total output across all producers rises. If firms leave the market, supply decreases (shifts left).
Weather and natural factors
For agricultural products and natural resources, weather plays a major role. A good harvest shifts supply right; drought, floods, or disease shift supply left.
- Favourable weather ā bumper crop ā supply shifts right
- Drought or flooding ā poor harvest ā supply shifts left
- Disease affecting livestock or crops ā supply shifts left
A past paper asked about changes in the wheat market. Bad weather reducing the wheat harvest is a supply-side change that shifts S left, raising the price of wheat.
Expectations
If firms expect the price to rise in the future, they may hold back supply today (shift left now) to sell later at the higher price. This is common in commodity markets like oil.
In the exam, always name the specific determinant causing the shift. Do not just write 'supply decreased' ā explain that, for example, 'rising fuel costs increased production costs, shifting supply to the left'.