📚 JAIIB · IE & IFS · Module B · Chapter 15
Theories of Interest
Classical theory says interest = reward for saving. Keynes said NO — interest is a reward for parting with liquidity. Then Hicks and Hansen synthesised both into the IS-LM framework. This chapter explains the theory behind every interest rate your bank charges.
⏱ 18 min read🎯 High Exam Weightage📈 IS-LM Curves⚡ 6 PYQs Inside
Sections 1–3 — Why This Chapter Matters
Interest rate theory is the foundation of every lending decision
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Sir, why do I need theory about interest rates — I just apply the rate the bank tells me!
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Banky, understanding WHY interest rates move helps you predict them! Classical theory says: more savings = lower interest. If households save more, loan rates fall. Keynes says: more money supply = lower interest. When RBI prints money (QE), rates fall — because liquidity preference is satisfied. IS-LM tells us: monetary policy shifts LM curve, fiscal policy shifts IS curve. Every RBI monetary policy action is IS-LM in practice. Understanding this gives you a 6-month loan book advantage.
Section 4 — Key Definitions and All Three Theories
Verified directly from textbook — Classical, Keynes, and Hicks-Hansen
Core Concept
Interest
“Payment made by a borrower for the use of money for a period of time”
One of Four Incomes
Interest is a payment made by a borrower for the use of a sum of money for a period of time. It is one of the four types of income — the others being rent, wages, and profit. Three elements can be distinguished in interest: (i) payment for the risk involved in making the loan; (ii) payment for the trouble involved; (iii) pure interest — a payment for the use of the money. Inflation aspect is also factored in. At any particular time, there is a prevailing rate of interest, regarded as a price determined by the demand to borrow in relation to the supply of loanable funds — this is pure interest.
📚 Classical Theory of Interest
- Also known as: Demand and Supply theory / capital theory / saving-investment theory / real theory
- Developed by: Marshall, Fisher, and Pigou
- Interest is determined by equilibrium of demand and supply of savings
- Interest = price paid for savings to meet demand for investment
- Interest is a real phenomenon determined by real factors (savings and investment)
- Demand for savings: from investors for business investment | Higher returns → more demand | Inversely related to interest rate (capital demand curve slopes DOWN)
- Supply of savings: determined by savings (positive relation with interest) | Interest = reward for abstinence/waiting | Supply curve slopes UP
- Equilibrium: where demand and supply of savings are EQUAL → equilibrium interest rate
🔑 Keynes’ Liquidity Preference Theory
- Book: The General Theory of Employment, Interest and Money
- Interest = purely monetary phenomenon
- Rate of interest determined by demand for money AND supply of money
- Theory name: Liquidity Preference Theory
- Interest = reward for parting with liquidity (NOT reward for saving)
- Two-asset economy: (1) Money (currency + current deposits — earn NO interest) and (2) Long-term bonds
- Key inverse relationship: Interest rate and bond prices are INVERSELY related — when interest rate falls, bond prices go up
- Three motives for holding money: Transactions, Precautionary, Speculative
- Higher interest rate → LOWER speculative demand for money
Keynes’ Three Motives for Holding Money (Cash)
💳 Transaction Motive
- Related to demand for money for current transactions
- Individuals: bridge gap between income and expenses = income motive
- Business: meet immediate demands (raw materials, wages, transport) = business motive
- Higher income → higher transactions motive demand for money
🛡️ Precautionary Motive
- Urge to hold cash for unforeseen contingencies
- Individuals: unexpected expenses (illness, accidents, unemployment)
- Businesses: weather bad times or benefit from unexpected opportunities
- Also influenced by level of income
📈 Speculative Motive
- Desire to keep resources liquid to profit from future changes in interest rates / bond prices
- If bond prices expected to rise (rates fall) → buy bonds now
- If bond prices expected to fall (rates rise) → sell bonds now, hold cash
- Higher rate of interest → LOWER speculative demand for money
- Lower rate → HIGHER speculative demand
Hicks-Hansen Synthesis — IS-LM Model
Synthesis
IS-LM Model
“Hicks + Hansen combined Classical and Keynes into one model”
Hicks & Hansen
Sir John Richard Hicks and Alvin Hansen synthesised the Classical and Keynes’ theories. The synthesis involves three steps:
(1) IS Curve — derived from Classical Theory. IS = Investment-Savings. Shows relationship between income and interest rate where savings = investment. IS curve slopes DOWNWARD (as income rises, equilibrium interest rate falls).
(2) LM Curve — derived from Keynesian Liquidity Preference Theory. LM = Liquidity Preference-Money Supply. Shows relationship between income and interest rate where money demand = money supply. LM curve slopes UPWARD (as income rises, money demand rises, so interest rate must rise to maintain equilibrium).
(3) Intersection of IS and LM gives the equilibrium rate of interest and the equilibrium level of income simultaneously. IS-LM model shows both monetary and real factors determine interest rate.
IS (downward, from Classical) intersects LM (upward, from Keynes) = equilibrium interest rate and income level
Section 5 — Exam Angle Points
All 6 PYQ answers plus high-frequency facts
✅ Must-Know Facts — Verified from PDF
- Interest is one of four types of income: The others are rent, wages, and profit (Money is NOT a type of income)
- Three elements of interest: (i) payment for risk (ii) payment for trouble (iii) pure interest
- Classical Theory also known as: Demand and supply theory / capital theory / saving-investment theory / real theory
- Classical Theory developed by: Marshall, Fisher, and Pigou
- Classical Theory: interest = reward for: Abstinence/waiting (NOT reward for parting with liquidity)
- Classical Theory: demand for capital is inversely related to: Interest rate (capital demand curve slopes downward)
- Keynes’ theory: interest = purely monetary phenomenon
- Keynes’ theory name: Liquidity Preference Theory
- Keynes: interest = reward for: Parting with liquidity (NOT reward for saving)
- Interest rate and bond prices: INVERSELY related (Keynes) — when rate falls, bond prices go up
- Three motives for holding money (Keynes): Transactions, Precautionary, Speculative
- Speculative demand for money: Higher interest → LOWER speculative demand | Lower interest → HIGHER speculative demand
- Two assets in Keynes’ two-asset economy: (1) Money (currency + current deposits, earn NO interest) (2) Long-term bonds
- Money demand curve: Downward sloping (demand for money INVERSELY related to interest rate)
- IS curve derived from: Classical Theory
- IS stands for: Investment-Savings
- IS curve slopes: Downward (income rises → equilibrium interest rate falls)
- LM curve derived from: Keynesian Liquidity Preference Theory
- LM stands for: Liquidity Preference-Money Supply equilibrium
- LM curve slopes: Upward (income rises → interest rate rises)
- IS-LM synthesis by: Sir John Richard Hicks and Alvin Hansen
- Money supply increases → LM curve shifts: Right → interest rate falls, national income rises
- Fiscal expansion → IS curve shifts: Right → interest rate rises, income rises
📝 All 6 PYQ Answers from PDF
Q1: Pick odd man out: (a) Rent (b) Interest (c) Wages (d) Money
Answer: (d) Money — Rent, Interest, Wages, Profit are the four types of income. Money is NOT a type of income.
Q2: According to J.M.Keynes, rate of interest and bond prices are related? (a) Inversely (b) Directly (c) Parallel (d) Horizontal
Answer: (a) Inversely — when interest rate falls, bond prices go up and vice versa
Q3: Keynes explained interest in terms of purely? (a) Real forces (b) Economic forces (c) Monetary forces (d) Social forces
Answer: (c) Monetary forces — Keynes: interest is a purely monetary phenomenon
Q4: The initials LM stand for? (a) Liquidity Model (b) Liquidity preference and Money supply equilibrium (c) Liquidity and Money Model (d) Liquidity and money
Answer: (b) Liquidity preference and Money supply equilibrium
Q5: IS curve is derived from? (a) Classical theory (b) Keynesian liquidity preference theory (c) Law of diminishing marginal utility (d) Law of equi-marginal utility
Answer: (a) Classical theory
Q6: LM curve is derived from? (a) Classical theory (b) Keynesian liquidity preference theory of interest (c) Law of diminishing marginal utility (d) Law of equi-marginal utility
Answer: (b) Keynesian liquidity preference theory of interest
Section 6 — Memory Tricks
Trick 1 — IS vs LM Source
IS = Classical | LM = Keynes
“IS = ‘I Save’ (Classical savings) | LM = ‘Liquidity-Money’ (Keynes)”
IS curve: Investment = Savings equilibrium → derived from Classical theory (which focuses on real savings and investment). LM curve: Liquidity preference = Money supply equilibrium → derived from Keynesian liquidity preference theory. Remember: IS is about the REAL sector (savings, investment). LM is about the MONETARY sector (money demand, money supply). IS slopes DOWN, LM slopes UP. Their intersection = equilibrium.
Trick 2 — Classical vs Keynes on Interest
Classical: reward for saving/abstinence | Keynes: reward for parting with liquidity
“Classical = Save to Earn. Keynes = Give Up Cash to Earn!”
Classical theory: Interest = reward for abstinence/waiting/saving. You save money → earn interest. Real phenomenon. Keynes: Interest = reward for parting with liquidity. You give up holding cash (buy a bond) → earn interest. Purely monetary. Key Keynes critique of Classical: savings are NOT interest-elastic (people save based on income, not interest rate). Q3 PYQ: Keynes = monetary forces. Q5: IS = Classical. Q6: LM = Keynes.
Trick 3 — Bond-Interest Inverse Relation
Interest rate ↑ → Bond prices ↓ (and vice versa)
“Bonds and rates are like a seesaw — one goes up, other goes down!”
Q2 PYQ answer: bond prices and interest rates are inversely related. When interest rates FALL → bond prices GO UP (people rush to buy bonds = demand up = price up). When interest rates RISE → bond prices FALL (better to hold money than bonds that lose value). This is why Keynes’ speculative demand for money works: low rates = hold money (bonds expensive, fear of loss); high rates = hold bonds.
Trick 4 — Three Motives TPS
Transactions + Precautionary + Speculative
“TPS = Transaction (daily needs) + Precaution (emergency) + Speculation (profit)”
Transactions = for daily spending (income motive for people, business motive for firms). Precautionary = for emergencies and unexpected events. Speculative = to profit from bond price/interest rate changes. TPS – remember like “TPS reports” from office. Key exam fact: Higher interest rate → LOWER speculative demand (people prefer bonds over cash when interest is high). Lower interest → HIGHER speculative demand (hold cash, fear bond prices falling).
Sections 7–9 — Flash Cards and Summary
Interest = One of 4 Incomes
Rent + Interest + Wages + Profit
Money is NOT an income type (Q1 PYQ odd one out = Money)
Classical Theory
Interest = reward for saving/abstinence
Marshall, Fisher, Pigou | Real phenomenon | Savings = Investment equilibrium
Keynes’ Theory Name
Liquidity Preference Theory
Interest = reward for parting with liquidity | Purely monetary phenomenon
Interest vs Bond Prices
INVERSELY related (Keynes)
Rate↑ → Bond price↓ | Rate↓ → Bond price↑
Three Money Motives
Transactions + Precautionary + Speculative
High rate → Low speculative demand | Low rate → High speculative demand
IS Curve
From Classical Theory | Slopes DOWNWARD
IS = Investment-Savings | Income↑ → Rate↓ | Fiscal expansion → shifts RIGHT
LM Curve
From Keynes’ Theory | Slopes UPWARD
LM = Liquidity pref-Money supply | Income↑ → Rate↑ | Money supply↑ → shifts RIGHT
IS-LM Synthesis by
Sir John Richard Hicks + Alvin Hansen
Intersection of IS and LM = equilibrium interest rate and income level
⚡ Chapter 15 Complete — Theories of Interest
- Interest = payment by borrower for use of money | One of four incomes (rent, interest, wages, profit) | Money is NOT income
- Three elements: payment for risk + payment for trouble + pure interest
- Classical Theory: interest = reward for abstinence/saving | Equilibrium of demand and supply of savings | Marshall, Fisher, Pigou | Real theory
- Demand for capital: inversely related to interest (demand curve slopes DOWN)
- Supply of savings: positively related to interest (supply curve slopes UP)
- Keynes: interest = purely monetary phenomenon = reward for parting with liquidity | Liquidity Preference Theory
- Interest rate and bond prices: INVERSELY related (key Keynes insight)
- Two-asset economy: (1) Money (no interest) and (2) Long-term bonds
- Three motives for holding money: Transactions + Precautionary + Speculative
- Higher interest → lower speculative demand (people buy bonds) | Lower interest → higher speculative demand (hold cash)
- Money demand curve: downward sloping (higher interest → less money demanded)
- IS curve: from Classical theory | Investment-Savings equilibrium | Slopes DOWN | Fiscal expansion shifts IS right
- LM curve: from Keynesian theory | Liquidity pref = Money supply | Slopes UP | Money supply increase shifts LM right (rate falls)
- IS-LM synthesis by Sir John Richard Hicks and Alvin Hansen | Intersection E = equilibrium rate and income
Banky says: “Now I know WHY RBI cuts rates during recession — it shifts the LM curve right!” 🎉
All 6 PYQs answered, Classical vs Keynes distinction clear, IS-LM framework understood, three motives locked in! 💪