Causes of Growth - Economic Growth

Actual growth is a rise in an economy's real GDP that uses up spare capacity — the economy produces more of what it can already produce (a short-run rise in output) (1). Potential growth is a rise in the economy's productive capacity — an increase in what it can produce when resources are fully employed, shown by a rightward shift of LRAS (the long-run trend) (1).

On a diagram with the price level (P) on the vertical axis and real GDP (Y) on the horizontal axis, draw a downward-sloping AD curve and an upward-sloping SRAS curve meeting at equilibrium E₁ (1 for a correct, labelled diagram).

Government spending (G) is a component of aggregate demand ($AD = C + I + G + (X - M)$), so a rise in G shifts AD rightward to AD₁ (1). Provided there is spare capacity, firms respond to the extra demand by raising output rather than only prices (1). Equilibrium moves from E₁ to E₂, so real GDP rises from Y₁ to Y₂ — this is actual growth, because the economy is using existing capacity more fully (1).

Investment is spending by firms (and government) on capital goods such as machinery, equipment and infrastructure, and it affects growth through two channels.

First, investment is a component of aggregate demand ($AD = C + I + G + (X - M)$), so a large rise in investment shifts AD rightward. Where there is spare capacity, this raises equilibrium real output — actual growth in the short run.

Second, and more importantly for growth, investment adds to the economy's capital stock. A larger, more modern capital stock raises the quantity and quality of a factor of production, so the economy's productive capacity increases. On a classical LRAS diagram this shifts the vertical LRAS rightward from LRAS to LRAS₁ (from Y₁ to Y₂): the economy can now produce more at full employment, with the price level tending to fall — this is potential growth.

Therefore a large rise in investment causes growth on both fronts: it raises AD (actual growth now) and, by building the capital stock, shifts LRAS right (potential growth later) — which is why investment is so valued for delivering sustainable, non-inflationary growth.

Long-run (potential) growth means the economy's productive capacity rises, shifting the LRAS curve rightward (on a classical diagram, from Y₁ to Y₂). This requires a rise in the quantity or quality of the factors of production. Two causes can bring it about.

Cause 1 — investment in physical capital. When firms and the government invest in new machinery, equipment and infrastructure, the economy's capital stock rises. A larger, more modern capital stock lets the same workforce produce more output, so capacity rises and LRAS shifts right. Investment is especially valuable because it also raises AD in the short run, giving both current and future benefits.

Cause 2 — better education and training (human capital). Improving workers' skills, knowledge and experience raises their productivity — each worker produces more per hour. A more productive, better-matched workforce raises the economy's capacity, shifting LRAS right. This is a core aim of supply-side policy and a driver of sustainable long-run growth.

On an LRAS diagram both causes shift the vertical LRAS from LRAS to LRAS₁ (Y₁ → Y₂), raising the level of output the economy can sustainably produce.

A large increase in net inward migration of working-age people affects growth through both aggregate demand and productive capacity.

The main effects. First, migrants spend and work, so consumption (C) rises and AD shifts right — where there is spare capacity this raises real output (actual growth). Second, and more durably, more workers raise the quantity of labour (and, if the migrants are skilled, the quality/human capital too), so the economy's productive capacity rises. On an AD/AS diagram with the price level (P) on the vertical axis and real GDP (Y) on the horizontal axis, the LRAS curve shifts rightward from LRAS to LRAS₁ (Y₁ → Y₂): the economy can now produce more at full employment — potential growth, with downward pressure on inflation. So migration can raise both actual and potential output.

Evaluation — how large and how beneficial? The size and desirability of the effect are uncertain.

First, it depends on the skills and employment of the migrants. Skilled migrants who fill labour shortages raise productivity and capacity strongly; if migrants struggle to find work, the capacity gain is smaller and unemployment could even rise.

Second, it depends on spare capacity and time frame. In the short run the AD boost may raise the price level more than output if the economy is near full capacity; the capacity (LRAS) benefit builds only over the long run as workers integrate.

Third, there are wider effects to weigh: extra demand for housing and public services (schools, healthcare) may strain infrastructure unless investment keeps pace, and effects on real GDP per head (rather than total GDP) depend on whether output rises faster than population.

Judgement. A large rise in net inward migration of working-age people will most likely raise both actual and potential output — a rightward AD shift now and a rightward LRAS shift over time. But the scale and net benefit depend on the migrants' skills and employment, on how much spare capacity exists, and on whether investment in housing and public services keeps pace. The effect is therefore best judged in context, and is most beneficial when migrants are readily employed and complemented by investment in capacity.

Long-run (potential) growth is a rise in the economy's productive capacity, shown by a rightward shift of LRAS (or an outward shift of the PPF), and it comes from a rise in the quantity and quality of the factors of production. Whether investment is the most important cause depends on the economy's circumstances and time frame.

The case that investment is most important. Investment — spending on machinery, equipment and infrastructure — raises the economy's capital stock, so the same workforce can produce more output; capacity rises and LRAS shifts right (Y₁ → Y₂). Investment is uniquely powerful for three reasons. First, it works on both sides: it is a component of AD (actual growth now) and it builds capacity (potential growth later), so it can deliver non-inflationary growth. Second, investment is the vehicle through which new technology is embodied — firms adopt better methods by buying new capital, so investment and innovation are intertwined. Third, investment in infrastructure (transport, energy, digital networks) raises the productivity of all other factors, giving economy-wide gains. Fast-growing economies (e.g. China, the East-Asian 'tigers') have typically combined high investment rates with export earnings that fund still more investment.

The case that other causes matter as much or more. First, human capital — education, training and skills — is arguably just as important: better-skilled workers raise productivity, and capital is far less productive without skilled people to operate it. Second, technology and innovation may be the deeper driver: in growth theory it is technological progress, not capital accumulation alone, that sustains long-run growth (capital alone runs into diminishing returns). Third, institutions and incentives — the rule of law, secure property rights, competition and sensible regulation — determine whether investment and enterprise happen at all; without them, investment is low and misallocated. Fourth, investment can be wasteful or misallocated (e.g. 'white-elephant' projects or excess capacity), so it is the quality, not just the quantity, of investment that matters.

Evaluation and judgement. Whether investment is 'most important' depends on context. In an economy short of capital and infrastructure, raising the investment rate is likely the single most powerful lever, and its dual AD/LRAS effect makes it especially valuable. But investment does not act in isolation: it needs human capital to be productive, technology to keep raising returns, and sound institutions to be allocated well — and it is subject to diminishing returns if pursued alone. The most defensible conclusion is that investment is one of the most important causes of long-run growth and often the key lever in capital-scarce economies, but it is not sufficient on its own: the strongest, most sustainable growth comes from combining investment with rising human capital, technological progress and supportive institutions. The 'most important' cause therefore depends on which factor is the binding constraint in a given economy.