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Determination of Income and Employment
Start here: why this chapter matters
This is Keynes's answer to the Great Depression (Chapter 1), in its simplest algebra and one famous diagram — the Keynesian cross. It explains why a fall in spending can cause a recession, why a government stimulus can work, why a rupee of new spending raises income by more than a rupee (the multiplier), and why everyone saving more can leave the economy poorer (the paradox of thrift). UPSC uses this logic in questions on fiscal stimulus, recession policy, demand-pull inflation and growth.
- Builds on: Chapter 1 (Keynes, the Great Depression, classical vs Keynesian), Chapter 2 (ex post identities, planned and unplanned inventories, C + I + G + X − M) and Chapter 3 (the interest rate, which here is held fixed but drives investment).
- Leads into: Chapter 5 (government spending and taxes in the same model — government spending and tax multipliers) and Chapter 6 (the open-economy multiplier with imports).
- Indian Economic Development: Chapter 3 (2020–21 contraction and rebound) and Chapter 6 (jobless growth — output and employment need not move together).
- UPSC: Prelims — fiscal stimulus (2010, 2011), recession policy (2021), demand-pull inflation (2021), what raises prices (2013), interest rates and investment (2014), capital–output ratio (1993, 1995, 2018). Mains GS3 — savings and growth potential (2017), potential GDP (2020).
| Word | What it means here |
|---|---|
| Ex ante / ex post | Planned (intended) value / actual (realised) value |
| Ceteris paribus | ‘Other things remaining equal’ — hold other variables fixed to study one |
| Autonomous | Independent of income (C̄, Ī, G) |
| Induced | Depends on income (cY) |
| MPC / MPS | Extra consumption / extra saving per extra rupee of income |
| APC / APS | Consumption / saving per rupee of income (C/Y, S/Y) |
| Aggregate demand (AD) | Total planned spending on final goods at each income level |
| Equilibrium income | Income at which planned spending equals planned output (AD = Y) |
| Investment multiplier | ΔY ÷ ΔĀ = 1 ÷ (1 − MPC) |
| Effective demand principle | With prices fixed and supply elastic, output is set by aggregate demand alone |
| Parametric shift | Movement of a line because a parameter (intercept or slope) changes |
| Full-employment income | Income at which all factors of production are employed |
At a glance — the six ideas to carry away
- Ex ante = planned; ex post = actual. Income is determined by planned demand.
- C = C̄ + cY: MPC = ΔC/ΔY (0 to 1), MPS = 1 − MPC; APC = C/Y, APS = S/Y, APC + APS = 1.
- AD = C̄ + Ī + cY; supply is the 45° line when prices are fixed and resources idle → Y* = (C̄ + Ī) ÷ (1 − c).
- NCERT: C = 40 + 0.8Y, I = 10 → Y* = 250; I = 20 → 300; multiplier = 1 ÷ (1 − c) = 1 ÷ MPS = 5.
- Paradox of thrift: MPC 0.8 → 0.5 cuts Y* from 250 to 100; saving stays 10 (= I).
- Equilibrium ≠ full employment: deficient demand (prices fall over time) or excess demand (prices rise); output set by effective demand.
1. Ex ante and ex post: plans versus outcomes
Chapter 2 measured consumption, investment and output ex post — what actually happened. To explain how income is determined, we need ex ante values — what people planned. NCERT's example: a producer plans to add ₹100 to her stock (planned investment ₹100); an unexpected rush of sales forces her to sell ₹30 from stock; actual inventory rises by 100 − 30 = ₹70 (actual investment ₹70).
- The identity Y ≡ C + I (ex post) always holds; the equilibrium condition Y = C + I (ex ante) holds only at equilibrium.
- Ex post saving always equals ex post investment; ex ante saving equals ex ante investment only in equilibrium.
2. The consumption function: MPC, MPS, APC, APS
The main determinant of consumption is income. NCERT's consumption function: C = C̄ + cY (4.1). C̄ is autonomous consumption — spending even at zero income; cY is induced consumption. c = MPC = ΔC/ΔY lies between 0 and 1 (inclusive): a rise in income can at most all be spent. Saving is income not consumed: S = Y − C, so MPS = s = ΔS/ΔY = 1 − c, and MPC + MPS = 1. Also APC = C/Y and APS = S/Y.
NCERT's Imagenia: C = 100 + 0.8Y. With no income, citizens still consume ₹100; if income rises by ₹100, consumption rises by ₹80. Worked extension: S = Y − C = −100 + 0.2Y. At Y = 100: C = 180, S = −80, APC = 1.8, APS = −0.8. At Y = 500: C = 500, S = 0 — the break-even point (APC = 1). At Y = 1,000: C = 900, S = 100, APC = 0.9, APS = 0.1. MPC stays 0.8 throughout; APC falls as income rises.
- Box: MPC = ΔC/ΔY (c); MPS = ΔS/ΔY = 1 − c, so s + c = 1; APC = C/Y; APS = S/Y.
- Fig. 4.1: a straight line Y = a + bX — intercept a on the vertical axis, slope b = tan θ. Fig. 4.2 applies it: consumption line with intercept C̄ and slope c = tan α.
- The point: every line in this chapter is defined by two parameters — an intercept (autonomous spending) and a slope (MPC). Change either and the line shifts (exercise Q3).
- APC can exceed 1 (at low incomes, through dissaving) but MPC normally stays below 1. As income rises, APC falls towards MPC.
- Poorer households usually have a higher MPC than richer ones — one reason transfers to the poor are often argued to give a bigger demand boost (UPSC 1979: unemployment insurance helps maintain consumption in a slump — an ‘automatic stabiliser’).
- Later theories (life-cycle, permanent income) argue consumption depends on long-run expected income, not just this year's — so temporary tax cuts may raise spending less than the simple model predicts.
- MPC + MPS = 1 and APC + APS = 1 — but MPC ≠ APC unless C̄ = 0.
- Autonomous consumption is the intercept, not the slope.
- Negative saving is possible; a negative MPC is not in this model.
3. Investment and aggregate demand
Investment is addition to physical capital (machines, buildings, roads) and to inventories. Investment goods are final goods, not intermediate. Investment depends heavily on the interest rate, but for simplicity NCERT takes it as autonomous: I = Ī (4.2) — a horizontal line. In a two-sector economy, AD = C + I = C̄ + Ī + cY; writing Ā = C̄ + Ī (total autonomous expenditure), AD = Ā + cY. C̄ is fairly stable; Ī fluctuates — the main source of booms and slumps.
- Fig. 4.3: investment as a horizontal line at height Ī — the same at every income.
- Fig. 4.4: AD obtained by vertically adding C and I: OM = C̄, OJ = Ī, OL = C̄ + Ī; AD is parallel to C.
- Fig. 4.5: aggregate supply as a 45° line — with prices fixed and idle resources, whatever GDP is demanded is supplied; at GDP of ₹1,000 (point A), supply is ₹1,000 (point B on the 45° line).
Adding government: with spending G and taxes T, disposable income is Y − T and Y = C̄ + Ī + G + c(Y − T). G − cT simply adds to the autonomous term, so the analysis is unchanged (Chapter 5 develops it). Without indirect taxes and subsidies, GDP equals national income, so Y is used for both.
- UPSC 2014: a fall in the interest rate raises investment expenditure — the link between Chapter 3 (money) and this chapter.
- With government: Y* = (C̄ + Ī + G − cT) ÷ (1 − c). Government-spending multiplier = 1 ÷ (1 − c); tax multiplier = −c ÷ (1 − c). With c = 0.8: +5 and −4. Raising G and T by the same amount raises Y by that amount (balanced-budget multiplier = 1) — see Chapter 5.
4. Equilibrium income: the Keynesian cross
Macroeconomics works in two stages: first with the price level fixed, then letting it vary. Why fix prices? (i) The economy is assumed to have unused machines, buildings and labour, so more can be produced without raising marginal cost; (ii) it is a simplifying first step. Supply then simply follows demand — the 45° line — and equilibrium is where the AD line cuts it.
Algebra (4.4): C̄ + Ī + cY = Y → Y(1 − c) = C̄ + Ī → Y* = (C̄ + Ī) ÷ (1 − c). NCERT's example: C = 40 + 0.8Y, I = 10 → Y = 50 + 0.8Y → Y* = 50 ÷ 0.2 = 250. Check: C = 40 + 200 = 240; AD = 240 + 10 = 250 ✓; saving = 250 − 240 = 10 = I ✓.
- Equilibrium is where AD = Y (equivalently planned S = planned I), not where C = Y.
- The 45° line is aggregate supply under fixed prices — not the consumption function.
- At equilibrium, unplanned inventory change is zero.
5. The investment multiplier
Autonomous demand can change through C̄, c or Ī (investment rises with easier credit and lower interest rates). NCERT's example: I rises from 10 to 20; AD shifts up in parallel from 50 + 0.8Y to 60 + 0.8Y; new Y* = 60 ÷ 0.2 = 300. Income rose by 50 — five times the rise in investment.
- AD₁ = Ā₁ + cY meets the 45° line at E₁ (Y₁*). Autonomous spending rises by ΔĪ, so AD₂ = Ā₂ + cY lies parallel above.
- At the old output Y₁*, demand is now Y₁*F — excess demand E₁F = ΔĪ. The new equilibrium is E₂ (Y₂*).
- Output rises by E₁G = E₂G, which is larger than ΔĪ = E₁F = E₂J: the multiplier in geometry.
- Columns: increase in consumption, aggregate demand and output/income in each round. Round 1: consumption 0, AD 10 (autonomous), output 10. Round 2: 0.8 × 10 in each column; round 3: 0.8² × 10; and so on.
- Total: 10 + 0.8 × 10 + 0.8² × 10 + … = 10 ÷ (1 − 0.8) = 50.
- The point: the extra output is paid out as factor incomes (since GDP = national income here), and 80% of each round's income is spent, creating the next round.
Multiplier = ΔY ÷ ΔĀ = 1 ÷ (1 − c) = 1 ÷ s (4.5). The larger the MPC, the larger the multiplier: c = 0.5 → 2; c = 0.75 → 4; c = 0.8 → 5; c = 0.9 → 10.
- Equation 4.5 prints the multiplier as 1 ÷ S (capital S, which elsewhere means total saving). It should read 1 ÷ s, the marginal propensity to save.
- The multiplier works both ways: a fall in investment cuts income by a multiple.
- Higher MPC → bigger multiplier; higher MPS → smaller.
- The multiplier works only with idle resources; at full employment extra demand raises prices, not output.
- Real-world multipliers are smaller than 1 ÷ (1 − c) because of leakages — taxes and imports (Chapters 5–6): with tax rate t and import share m, roughly 1 ÷ [1 − c(1 − t) + m].
- Estimates of India's fiscal multipliers suggest public capital spending raises output by more than revenue spending or tax cuts — the usual argument for capital expenditure in stimulus packages (e.g. after 2020). Treat specific numbers as model-dependent.
6. The paradox of thrift
NCERT's example: at Y* = 250, people suddenly become thriftier (fearing war or disaster) — MPC falls from 0.8 to 0.5 (MPS rises from 0.2 to 0.5). At income 250, consumption falls by (0.8 − 0.5) × 250 = 75: excess supply of 75. Output and income fall by 75; consumption falls by 0.5 × 75; and so on. Total fall = 75 ÷ (1 − 0.5) = 150, so the new equilibrium is 100 (check: 50 ÷ (1 − 0.5) = 100).
Saving before: 250 − (40 + 0.8 × 250) = 250 − 240 = 10. Saving after: 100 − (40 + 0.5 × 100) = 100 − 90 = 10. Total saving is unchanged, because in equilibrium saving = investment, and investment is fixed at 10. If investment itself fell with income, total saving would actually decline — hence NCERT's ‘decline or remain unchanged’.
- A change in Ā shifts the AD line in parallel; a change in c swings it about its intercept. A higher MPS (lower MPC) makes AD flatter, swinging it down.
- Fig. 4.8: AD₁ = Ā + c₁Y meets the 45° line at E₁ (Y₁*); AD₂ = Ā + c₂Y, flatter, meets it at E₂ (Y₂*), lower. With Ā = 50: Y₁* = 50 ÷ 0.2 = 250 and Y₂* = 50 ÷ 0.5 = 100 — a fall of 150.
- The point: a parametric change in behaviour, not in autonomous spending, can also move equilibrium income — and the effort to save more is defeated.
- In a slump with idle resources (Keynes's case), more saving cuts demand and income — the paradox holds. This is why governments in 2008–09 and 2020 tried to support spending.
- In the long run, or at full employment, saving funds investment, which builds capital and raises future output — the classical point, and the basis of high-saving East Asian growth. UPSC Mains 2017 asked whether the saving rate is the most effective driver of India's growth potential (section 8).
- So the answer depends on whether the economy is demand-constrained or supply-constrained.
7. Full employment, excess and deficient demand
Equilibrium output also fixes employment, given other factors. Full-employment income is where all factors are employed. Equilibrium at AD = Y need not be at full employment — if left alone, income stays there even with unemployment. If equilibrium output is below full employment, demand is not enough: deficient demand, which tends to lower prices in the long run. If demand exceeds the full-employment level of output: excess demand, which tends to raise prices.
Worked example (our numbers on NCERT's model). Let full-employment income Yf = 300, C = 40 + 0.8Y. (a) With I = 10: AD at Yf = 40 + 240 + 10 = 290 — demand falls short by 10 (a deflationary gap); equilibrium is 250, so 50 of potential output is lost. Raising autonomous spending by 10 (I to 20, or G by 10) raises Y by 10 × 5 = 50, to 300. (b) With I = 30: AD at Yf = 310 — an inflationary gap of 10. The model's ‘equilibrium’ would be 70 ÷ 0.2 = 350, but real output cannot exceed 300; prices rise instead.
- Deficient demand / recession: raise public spending, cut taxes, cut interest rates and reserve ratios. UPSC 2010: a fiscal stimulus = cutting tax rates and raising government spending (not abolishing subsidies); UPSC 2011: fiscal stimulus = intense government action to boost economic activity; UPSC 2021: in a recession, the most likely step is more spending on public projects.
- Excess demand / demand-pull inflation: cut spending, raise taxes, raise interest rates, sell bonds. UPSC 2021: demand-pull inflation is fed by expansionary policies, fiscal stimulus and higher purchasing power — not by wage indexation (cost-push) or rising interest rates. UPSC 2013: prices can rise from more money, less output or more effective demand — all three.
- Potential GDP (UPSC Mains 2020): the output an economy can produce at full employment of its resources without accelerating inflation; the difference from actual GDP is the output gap (negative = deficient demand, positive = excess demand).
8. Keynes versus the classics — and growth in the long run
This chapter's model is deliberately short-run: prices fixed, interest fixed, capacity idle. In the long run, output is limited by capacity, and capacity grows through saving and investment. A simple growth rule (Harrod–Domar, Beyond NCERT): growth ≈ saving (investment) rate ÷ incremental capital–output ratio (ICOR). With a saving rate of 30% and ICOR 4, growth ≈ 7.5%; if capital is used less efficiently (ICOR 5), the same saving gives only 6%.
- UPSC 1995 and 2018: despite high saving and capital formation, growth may stay low because of a high capital–output ratio; UPSC 1993: slow per capita growth came from a high capital–output ratio and fast population growth.
- Mains GS3 2017: is the saving rate the most effective factor for India's growth potential? Argue both: saving finances investment (and India's saving rate rose sharply in the 2000s), but growth also needs productivity (ICOR), human capital, technology, institutions, infrastructure and demand — a high saving rate with weak demand can even slow growth in the short run (paradox of thrift).
- Mains GS3 2020: potential GDP and its determinants — labour force and skills, capital stock, technology and productivity; constraints in India include low female labour participation, infrastructure gaps, low R&D, informality and regulatory frictions.
NCERT exercise — answer outlines
Try each question yourself first. The chapter has no in-text questions; question 5 is a numerical, worked in full.
1. What is marginal propensity to consume? How is it related to marginal propensity to save?
2. What is the difference between ex ante investment and ex post investment?
3. What do you understand by ‘parametric shift of a line’? How does a line shift when its (i) slope decreases, and (ii) its intercept increases?
4. What is ‘effective demand’? How will you derive the autonomous expenditure multiplier when price of final goods and the rate of interest are given?
5. Measure the level of ex-ante aggregate demand when autonomous investment and consumption expenditure (A) is ₹50 crore, MPS is 0.2 and level of income (Y) is ₹4,000 crore. State whether the economy is in equilibrium or not (cite reasons).
Ex ante AD = Ā + cY = 50 + 0.8 × 4,000 = 50 + 3,200 = ₹3,250 crore.
Output Y = 4,000 > AD = 3,250 → not in equilibrium: excess supply of ₹750 crore, unplanned inventories pile up, firms will cut output.
Equilibrium: Y* = 50 ÷ (1 − 0.8) = ₹250 crore. (At Y = 250: AD = 50 + 200 = 250 ✓.)
6. Explain ‘Paradox of Thrift’.
What to remember
Numbers
One-liners
- Ex ante = planned; ex post = actual.
- C = C̄ + cY; MPC + MPS = 1; APC + APS = 1.
- AD = Ā + cY; equilibrium where AD meets the 45° line.
- Y* = Ā ÷ (1 − c).
- Multiplier = 1 ÷ (1 − MPC) = 1 ÷ MPS.
- Change in Ā shifts AD in parallel; change in c swings it.
- Paradox of thrift: more saving by all, no more total saving.
- Equilibrium can be below full employment (deficient demand).
- Excess demand at full employment raises prices, not output.
Traps to avoid
- Equation 4.5's ‘1 ÷ S’ means 1 ÷ s (MPS), not total saving.
- Higher MPC → larger multiplier.
- The identity Y ≡ C + I always holds ex post; Y = C + I (ex ante) only in equilibrium.
- The 45° line is aggregate supply, not consumption.
- Paradox of thrift: saving stays unchanged (fixed I) or falls (induced I) — never rises.
- Output cannot exceed full-employment output; excess demand shows up as inflation.
- Fiscal stimulus = tax cuts + more spending; abolishing subsidies is contractionary (UPSC 2010).
- Wage indexation is cost-push, not demand-pull (UPSC 2021).
- A lower interest rate raises investment, not saving (UPSC 2014).
- High saving with slow growth points to a high capital–output ratio (UPSC 1995, 2018).
How to strategise
Prelims — what UPSC asks
- Demand management: fiscal stimulus (2010, 2011), recession policy — public projects (2021), demand-pull inflation causes (2021), causes of rising prices including effective demand (2013), unemployment insurance maintains consumption (1979).
- Investment and growth: lower interest raises investment (2014); capital–output ratio and slow growth (1993, 1995, 2018).
- Expect statement questions on MPC/MPS, the multiplier's direction, and ex ante vs ex post — practise with numbers: Y* = Ā ÷ (1 − c).
Mains — where it appears and how to answer
- GS3 2017: saving rate and growth potential — saving finances investment, but also ICOR/productivity, human capital, technology, demand; India's saving rate trend; paradox of thrift caveat.
- GS3 2020: potential GDP — definition, output gap, determinants (labour, capital, total factor productivity), and Indian constraints.
- Answer frame for any recession/stimulus question: diagnose (deficient demand, output gap) → mechanism (multiplier, why capital spending has larger effects) → instruments (fiscal and monetary) → limits (inflation near capacity, fiscal space, crowding out) → balanced conclusion.
- Draw the Keynesian cross with a shift, or the gap diagram at full employment; quote NCERT's 250 → 300 example.
Self-check
Tap an option. NCERT's own exercise questions come first; the rest test the figures and common confusions.
1. If MPC is 0.75, the investment multiplier is:
2. C = 60 + 0.8Y and I = 40. Equilibrium income is:
3. At an income where planned aggregate demand is less than output, there will be:
4. Which statement about the propensities is correct?
5. In NCERT's paradox-of-thrift example, MPC falls from 0.8 to 0.5 with autonomous spending 50. What happens to total saving?
6. A decrease in the slope of the aggregate demand line, with the intercept unchanged, shows:
7. Which of the following is NOT a likely cause of demand-pull inflation?
UPSC questions from this chapter
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