SRAS shifts change what firms produce today. LRAS shifts change what the country is capable of producing at all. Only four kinds of change can do that, and they are the same four things that push a production possibilities curve outwards.
📚 What you need to know
LRAS shows the potential output of an economy when every resource is fully used.
Four things shift it right: better or more factors of production, technological advances, efficiency gains, and stronger institutions.
A rightward LRAS shift is the definition of long-run economic growth.
On a Keynesian diagram the same shift moves the whole AS curve right, including the vertical section.
An LRAS shift corresponds to a PPC shifting outwards.
SRAS shifts do not change potential output — that is the difference examiners test.
The four drivers
Driver
What it means
Concrete example
Quantity or quality of factors of production
More workers, more land, more capital — or the same amount but better
Opening up skilled migration; training school leavers so they are more productive
Technological advance
New knowledge lets the same inputs produce more
New materials, better crop varieties, faster computing
Efficiency improvements
Process innovation raises output per worker per hour
Automating an assembly line that used to be done by hand
Institutions
The rules and organisations that let markets work well
Reliable courts, competition law, banks that lend to small firms
Institutions are the driver students forget, and it is often the most powerful one. A country can have oil, workers and machines and still produce very little if contracts are not enforced and nobody can borrow.
Showing it on a diagram
Both models draw the same idea in their own style. Learn both, because the question will tell you which one to use.
The classical diagram shows the bonus of supply-side growth: output up and prices down. That is why supply-side policy is often called the answer to growth without inflation.
Reading the classical diagram properly
🧩 Step by step
The economy starts in long-run equilibrium at AP₁ and YFE.
Something raises capacity — say a large improvement in education, which raises the quality of labour.
The whole LRAS shifts right, from LRAS₁ to LRAS₂.
AD has not moved, so the new equilibrium is further down the AD curve.
Output rises to YFE1 and the average price level falls to AP₂.
This is long-run growth: the potential of the economy is genuinely bigger.
Time lag warning. Almost every LRAS policy is slow. Training a nurse takes years; a railway takes a decade. In evaluation, always weigh the long wait against the fact that the effect, once it arrives, is permanent.
Worked example
WORKED EXAMPLE
SRAS shift or LRAS shift?
Classify each of the following: (a) the government cuts the tax on diesel; (b) a national programme retrains 200,000 unemployed workers as electricians; (c) a new port halves the time it takes to move goods.
(a) Diesel tax cutSRAS shifts rightIt lowers costs today. It does not add any new productive capacity, so LRAS is unchanged.(b) Retraining programmeLRAS shifts rightIt raises the quality of labour, a factor of production. The economy can genuinely produce more.(c) New portBoth, in orderLower transport costs shift SRAS right straight away; the extra infrastructure is new capital, so LRAS shifts right too.Ask: does it change costs, or capacity?
💡 Exam tip
Use the phrase “potential output” when you talk about LRAS. It signals to the examiner that you know the difference.
On the Keynesian diagram, shift the whole curve, including the flat section, not just the vertical part.
Link LRAS to the PPC: a rightward LRAS shift is an outward PPC shift. That cross-topic link earns credit.
Name the driver. “Education improves the quality of labour” beats “the economy gets better”.
Bring in time lags and opportunity cost for evaluation — supply-side policy is slow and expensive.
Remember AD is normally held constant in these diagrams unless the question says otherwise.
⚠️ Common mix-up
Calling a fall in oil prices an LRAS shift. It is a cost change, so it shifts SRAS.
Thinking higher AD shifts LRAS. Demand cannot create capacity by itself.
Shifting only the vertical section of the Keynesian curve. The whole curve moves.
Forgetting the price level falls in the classical diagram when LRAS shifts right and AD is fixed.
Listing “more money” as a driver. Money is not a factor of production.
Assuming any government spending shifts LRAS. Spending on capital and skills might; spending on benefits does not.
Up next: Macroeconomic Equilibrium and Output Gaps — putting AD and AS together to find where the economy actually settles.
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