Aggregate Supply (AS)
Edexcel International A-Level Economics· 2.3.3· 18 min read
1. 1. Aggregate Supply: Core Definition, Movements vs Shifts★★☆☆☆⏱ 4 min
Aggregate Supply
The total volume of goods and services that all producers in an economy are willing and able to supply at each given price level in a given time period.
Example:
At a price level of 105, UK firms are willing to supply £2.2tn of real output annually.
AS is a purely macroeconomic concept, distinct from micro-level firm supply curves (covered in Unit 3). Changes to AS fall into two categories: movements along the curve and shifts of the curve.
Movement along AS: Caused only by changes in the general price level, ceteris paribus. Higher prices increase firm profit margins, raising the quantity of output supplied, and vice versa.
Shift of AS: Caused by non-price factors that change aggregate production costs or total productive capacity. The entire curve shifts left (lower output at all prices) or right (higher output at all prices).
Which of the following causes a movement along the SRAS curve?
A: 10% fall in the general price level
B: 20% rise in global raw material costs
C: 5% cut in corporation tax rates
D: 15% increase in labour productivity
Reveal answer
A —Movements along AS only result from changes to the price level. All other options are non-price factors that shift the AS curve.
State whether each of the following causes a movement along or shift of the AS curve: a) 10% increase in the UK CPI, b) 20% rise in global natural gas prices.
- 1
a) A rise in CPI is an increase in the general price level of the economy.
- 2
This only changes the quantity of output supplied along the existing AS curve, so it is a movement along AS.
- 3
b) A rise in natural gas prices is a non-price factor that increases production costs for most firms.
- 4
This changes the quantity of output firms are willing to supply at every price level, so it is a leftward shift of the AS curve.
Exam tip:
When explaining movements vs shifts in exam responses, always explicitly state whether the change is to the price level (movement) or a non-price supply factor (shift) to secure full analysis marks.
2. 2. Short-Run Aggregate Supply (SRAS): Curve and Shifters★★★☆☆⏱ 5 min
Short-Run Aggregate Supply (SRAS)
The total output supplied in an economy when the price of factor inputs (e.g. raw materials, energy) are fixed, and at least one factor of production (usually capital) is inflexible.
SRAS slopes upward because higher price levels increase firm profit margins (with fixed input costs), incentivising firms to expand output by using existing labour and capital more intensively. The core SRAS shifters specified in the Edexcel syllabus are listed below:
Raw material and energy costs: Higher input costs increase production costs, shifting SRAS left; lower costs shift SRAS right.
Exchange rates: Domestic currency depreciation raises import costs for raw materials, shifting SRAS left; appreciation shifts SRAS right.
Tax rates: Higher indirect taxes (VAT, fuel duty) or corporation tax increase production costs, shifting SRAS left; tax cuts shift SRAS right.
Using a diagram, explain the impact of a 15% depreciation of the Indian rupee on India’s SRAS curve.
- 1
Draw a correctly labelled SRAS diagram: y-axis = Price Level (PL), x-axis = Real Output (Y), initial upward sloping SRAS curve labelled SRAS1.
- 2
A rupee depreciation makes imported raw materials and energy more expensive for Indian firms, increasing their production costs at every price level.
- 3
This causes the SRAS curve to shift left from SRAS1 to SRAS2, with output lower at every given price level. Mark the shift with a left-facing arrow between the two curves.
- 4
Link to context: This would lead to higher domestic prices and lower short-run output, ceteris paribus.
Exam tip:
For 4-mark SRAS diagram questions, you get 2 marks for correctly labelled axes and curves, and 2 marks for a clearly marked shift arrow and explicit link to the question context.
3. 3. Long-Run Aggregate Supply (LRAS): Keynesian vs Classical Models★★★★☆⏱ 5 min
Long-Run Aggregate Supply (LRAS)
The total output supplied in an economy when all factor prices are fully flexible, and the economy is operating at its maximum potential productive capacity.
The Edexcel specification requires you to know two competing LRAS models, each with different assumptions about long-run wage and price flexibility:
Classical LRAS: Perfectly vertical at full employment output (). Assumes wages and prices are perfectly flexible in the long run, so any short-run deviation from full employment will automatically self-correct. Long-run output is always at , regardless of the price level.
Keynesian LRAS: Reverse L-shaped curve, with three segments:
1. Horizontal segment: High spare capacity, firms can increase output without raising prices (unused labour and capital, downward-sticky wages).
2. Upward sloping segment: Spare capacity runs out, industry bottlenecks emerge, so prices rise as output increases.
3. Vertical segment: At , no spare capacity remains, so higher demand only raises prices.
Compare the shape of the Keynesian and classical LRAS curves, and outline one key assumption underlying each.
- 1
Classical LRAS is a perfectly vertical curve at the full employment level of output ().
- 2
Key assumption: Wages and prices are fully flexible in the long run, so the economy always returns to full employment output automatically after any short-run shock.
- 3
Keynesian LRAS is a reverse L-shaped curve: horizontal at low output levels, upward sloping at medium output, and vertical at .
- 4
Key assumption: Wages are sticky downwards (workers resist nominal wage cuts), so economies can operate below full employment for extended periods if aggregate demand is insufficient.
Exam tip:
The difference between the two LRAS models is a strong evaluation point for extended response questions: the impact of any demand or supply shock depends on which long-run model you assume is correct.
4. 4. Determinants of LRAS Shifts and Potential Output★★★☆☆⏱ 4 min
Shifts in the LRAS curve represent changes to the economy's maximum potential output. A rightward shift means the economy can produce more goods and services at full employment, while a leftward shift means potential output has fallen. The core LRAS shifters specified in the Edexcel syllabus are:
Technology: Improved technology increases labour and capital productivity, shifting LRAS right.
Productivity: Higher output per unit of labour or capital increases total possible output, shifting LRAS right.
Education and skills: Better workforce education and skills raise labour productivity, shifting LRAS right.
Regulation and tax: Less burdensome regulation and lower business tax incentivise investment, shifting LRAS right; excessive regulation or high tax shifts LRAS left.
Demography and net migration: Positive net migration of working-age people increases the labour force, shifting LRAS right; an ageing population reduces the labour force, shifting LRAS left.
Competition policy: Policies that increase market competition (e.g. anti-monopoly rules) incentivise efficiency and innovation, shifting LRAS right.
Analyse the impact of a UK government policy that increases the number of skilled work visas for foreign tech workers on the UK’s LRAS curve.
- 1
Increasing skilled work visas will lead to an increase in net migration of working-age, skilled labour into the UK.
- 2
This increases the size of the UK labour force, and also raises average labour productivity due to the high skill level of the migrant workers.
- 3
Both factors increase the maximum potential output of the UK economy.
- 4
This causes the LRAS curve to shift to the right, from LRAS1 to LRAS2, raising the full employment level of output from to .
Exam tip:
When explaining LRAS shifts, always build a full logical chain of reasoning (e.g. higher net migration → larger labour force → higher potential output → rightward LRAS shift) to secure maximum analysis marks.
5. Common Pitfalls
Wrong move:
Confusing a movement along the AS curve with a shift when the price level changes.
Why:
Only changes in the general price level cause movements; all other supply factors cause shifts. Candidates often mix these up and lose analysis marks.
Correct move:
Explicitly state: 'A change in the price level causes a movement along the existing AS curve, while a change in non-price production costs or capacity causes a shift of the entire AS curve.'
Wrong move:
Drawing the classical LRAS as upward sloping, or the Keynesian LRAS as vertical at all output levels.
Why:
The spec explicitly requires distinct shapes for both LRAS models, and incorrect diagram shape loses all diagram marks.
Correct move:
Label your LRAS curve explicitly as either Keynesian or classical when drawing it, and match the shape to the model you are referencing.
Wrong move:
Listing raw material costs as an LRAS determinant.
Why:
Raw material and energy cost changes are short-run factors that do not affect the economy's long-run productive capacity, so they only shift SRAS.
Correct move:
Memorise the separate lists of SRAS and LRAS shifters, and explicitly state which time frame you are referring to in your response.
Wrong move:
Conflating macro AS curves with micro firm-level marginal cost curves.
Why:
Firm-level cost curves are a microeconomic concept (Unit 3 content), and conflating them with AS leads to incorrect macro analysis.
Correct move:
Always refer to aggregate production costs across the whole economy when discussing AS, not individual firm costs.
Wrong move:
Forgetting to label axes and curve shift arrows when drawing AS diagrams.
Why:
4-mark diagram questions award 2 marks for correct labels, so unlabelled diagrams lose half the available marks even if the shape is correct.
Correct move:
Always label the y-axis 'Price Level (PL)' and x-axis 'Real Output (Y)', mark curves clearly, and add an arrow to show the direction of any shift.
6. Quick Reference Cheatsheet
Concept | Key Features | Shifters | Diagram Shape |
|---|---|---|---|
Aggregate Supply (AS) | Total output of all firms in the economy at each price level | N/A: split into SRAS/LRAS | Varies by time frame |
SRAS | Short run: factor prices fixed, capital inflexible | Raw material/energy costs, exchange rates, tax rates | Upward sloping |
Classical LRAS | Long run: wages/prices fully flexible, always at | Technology, productivity, education, regulation, migration, competition policy | Vertical at full employment output () |
Keynesian LRAS | Long run: wages sticky downwards, possible spare capacity | Same as classical LRAS shifters | Reverse L-shape: horizontal → upward sloping → vertical at |
7. Frequently Asked
What is the difference between a movement and shift of the AS curve?
A movement along the AS curve is only caused by a change in the general price level, ceteris paribus. A shift of the entire AS curve is caused by non-price factors that change aggregate production costs or productive capacity, affecting output at every price level.
Do I need to draw both Keynesian and classical LRAS shapes in the exam?
Yes, the Edexcel specification requires you to know both shapes. Always explicitly label which LRAS model you are using in your response to avoid losing marks, and state the relevant underlying assumption if required.
Can I reference wage changes as an SRAS shifter?
Only if the question explicitly mentions wage changes. The core SRAS shifters specified for Unit 2 are raw material/energy costs, exchange rates, and tax rates, so prioritise these in generic responses.
Going deeper
What's Next
Now that you have mastered aggregate supply, you are ready to move on to aggregate demand and AD-AS equilibrium, the next core topic in Edexcel IAL Economics Unit 2. You will apply your knowledge of SRAS and LRAS shifts to analyse how macroeconomic shocks affect real output, unemployment, and price levels in both the short and long run. You will also draw on your AS understanding when studying economic growth (the topic after equilibrium) and supply-side policies, which are designed specifically to shift the LRAS curve right to increase potential output over time. Make sure you practice drawing all required AS diagrams repeatedly, as they are a core component of extended response questions worth up to 20 marks in your Unit 2 exam.