Theories of Interest — Why Banks Charge What They Charge
Classical theory (savings = investment), Keynes’ Liquidity Preference (3 motives for holding money), IS-LM curve model (Hicks-Hansen synthesis), and how monetary/fiscal policy affects interest rates.
Banky Discovers Why Interest Rates Exist! 💹
Interest is YOUR bread and butter — your bank earns from the SPREAD between deposit and loan rates. But why do interest rates exist? Why do they change? Two great economists disagreed — and their debate shapes banking today.
Why Read This Chapter?
Interest rates ARE your bank’s business model
Exam Marks
3-5 questions — Classical vs Keynes theory, 3 motives for holding money, IS-LM meaning, bond prices inversely related to interest rates. Very conceptual!
Career Growth
Treasury managers and ALM officers use IS-LM analysis daily. This chapter = promotion to treasury department
Real Life
You’ll understand why RBI’s rate decisions immediately affect your home loan EMI and FD returns
How Will It Benefit You?
Real career advantages
What Is This Chapter About?
30-second summary
Key Definitions — Banky Asks, Mentor Explains
Every term explained like you’re 10
Banky’s Understanding: Interest is one of 4 types of income (rent, wages, profit, interest). Three elements: (1) Payment for risk of making the loan, (2) Payment for trouble involved in lending, (3) Pure interest — payment for use of money itself. Rate differences between loans are due to differences in risk/trouble. Unsecured moneylender charges MORE than bank (higher risk). Government pays MORE on long-term bonds than short-term (more time = more uncertainty).
Banky’s Understanding: Also called demand-supply theory / capital theory / saving-investment theory. Developed by Marshall, Fisher, Pigou. Interest = price determined by supply of savings (thrift/time preference) and demand for investment (productivity of capital). Key insight: as more capital is invested, marginal productivity decreases (law of diminishing returns). Producer invests until marginal productivity = interest rate. Higher interest → more savings supplied, less investment demanded. The ‘classical’ in Classical = focuses on real factors (savings, investment), NOT monetary factors.
Banky’s Understanding: Keynes said interest is determined by demand for money (liquidity preference) and supply of money (fixed by RBI). Three motives for holding cash: (1) Transaction — for daily expenses (income + business motive), (2) Precautionary — for unexpected emergencies (illness, accidents), (3) Speculative — to profit from future changes in bond prices/interest rates. Key insight: bond prices and interest rates are INVERSELY related. If rates expected to RISE → sell bonds now (before price falls) → hold cash. If rates expected to FALL → buy bonds now (before price rises).
Banky’s Understanding: Transaction Motive: Money for daily expenses — bridging gap between income and expenditure. Individuals (income motive) and businesses (business motive). Precautionary Motive: Cash for unforeseen emergencies — illness, accidents, unemployment. Speculative Motive: Holding cash to profit from expected changes in bond prices. If interest rates expected to RISE → bond prices will FALL → hold cash (avoid bond losses). Higher interest rate → LOWER speculative demand for money.
Banky’s Understanding: Derived from Classical Theory. IS = Investment-Savings equilibrium. At each income level, there’s a rate of interest where savings equals investment. As income rises, savings increase, so interest rate falls to maintain equilibrium. Therefore IS curve slopes DOWNWARD. Steepness depends on how sensitive investment is to interest rate changes. Fiscal expansion (government spending ↑) shifts IS curve RIGHT → higher interest rate + higher income.
Banky’s Understanding: Derived from Keynes’ Liquidity Preference Theory. LM = Liquidity preference-Money supply equilibrium. As income rises, money demand for transactions increases. With fixed money supply, this extra demand pushes interest rates UP. Therefore LM curve slopes UPWARD. Monetary expansion (money supply ↑) shifts LM curve RIGHT → lower interest rate + higher income. Money supply is controlled by RBI.
Banky’s Understanding: The Hicks-Hansen synthesis combines Classical (IS) and Keynes (LM) theories. IS slopes DOWN, LM slopes UP — intersection = equilibrium interest rate AND income level. At this point: (1) investment = savings, AND (2) money demand = money supply. Both real and monetary factors matter! A determinate theory needs: (1) investment-demand function, (2) saving function, (3) liquidity preference function, (4) quantity of money supply.
Banky’s Understanding: This is Keynes’ crucial insight: bond prices and interest rates are INVERSELY related. Why? If you hold a bond paying 8% and new bonds pay 10%, nobody wants YOUR 8% bond — its price FALLS. If new bonds pay 6%, everyone wants YOUR 8% bond — its price RISES. This inverse relationship drives the speculative motive: if you expect rates to RISE (bond prices fall), you sell bonds and hold cash.
Chapter Explained in Simple Stories
So easy even Banky’s nephew understands
📚 Block 1: Classical vs Keynes — The Great Interest Rate Debate
Two theories fought over WHY interest rates exist:
🏛️ Classical Theory (Marshall/Fisher/Pigou): Interest is determined by REAL factors — the supply of savings and demand for investment. People save more when rates are high (reward for patience). Businesses invest more when rates are low (cheaper to borrow). Where savings = investment = the interest rate. Simple supply-demand! But Keynes said this was incomplete…
💡 Keynes’ Theory (1936): Interest is not about savings — it’s about LIQUIDITY PREFERENCE. People hold money for 3 reasons: Transaction (daily needs), Precautionary (emergencies), Speculative (profit from bond price changes). The interest rate is the REWARD for giving up liquidity. And here’s the bombshell: it’s NOT interest that equalizes savings and investment — it’s CHANGES IN INCOME!
Both were partially right. That’s why Hicks and Hansen created the IS-LM model — combining both!
💰 Block 2: The 3 Reasons You Keep Cash — Keynes’ Insight
Keynes asked a simple question: WHY do people hold cash instead of investing in bonds? Three reasons:
🛒 Transaction Motive (T): You need cash for daily expenses — chai, auto, groceries. Businesses need cash for wages, raw materials. This is money for the GAP between when you earn and when you spend.
🏥 Precautionary Motive (P): You keep emergency cash — what if you get sick? What if your car breaks down? This is your financial safety net. Both individuals AND businesses do this.
📈 Speculative Motive (S): This is the clever part. You keep cash to PROFIT from future market moves. If you expect interest rates to RISE (meaning bond prices will FALL), you hold cash now and buy bonds later at lower prices. If rates are HIGH → speculative demand for money is LOW (everyone buys bonds). If rates are LOW → speculative demand is HIGH (everyone holds cash, waiting).
Key exam fact: bond prices and interest rates are INVERSELY related!
📊 Block 3: IS-LM — The Model That Runs Central Banking
Hicks and Hansen said: ‘Let’s COMBINE Classical and Keynes!’ Result: the IS-LM model.
IS Curve (from Classical): Shows where Savings = Investment at each income level. Slopes DOWNWARD — as income rises, interest rate falls. Derived from the real economy (goods market). Fiscal expansion (govt spending ↑) shifts IS RIGHT → interest ↑ + income ↑.
LM Curve (from Keynes): Shows where Money Demand = Money Supply at each income level. Slopes UPWARD — as income rises, money demand rises, so interest rate rises too. Monetary expansion (money supply ↑) shifts LM RIGHT → interest ↓ + income ↑.
Where IS meets LM = EQUILIBRIUM — the one interest rate and income level where BOTH the goods market AND money market are balanced. This is exactly what RBI analyses when setting repo rate!
Policy effects: Fiscal expansion → IS right → ↑r, ↑Y. Monetary expansion → LM right → ↓r, ↑Y. Contractionary policies → opposite shifts.
Exam Angle — Every Testable Point
All facts, numbers, definitions JAIIB tests
✅ Must-Know Facts — Highest Probability
- Interest: one of 4 income types (rent, wages, profit, interest) — 3 elements: risk, trouble, pure interest
- Classical Theory: also called demand-supply / capital / saving-investment / REAL theory
- Classical: interest determined by supply of savings + demand for investment (Marshall, Fisher, Pigou)
- Classical: marginal productivity of capital decreases with more investment (diminishing returns)
- Classical: investment continues until marginal productivity = interest rate
- Keynes: interest = reward for parting with liquidity — Liquidity Preference Theory
- Keynes: interest determined by demand for money (liquidity preference) + supply of money (RBI fixes)
- Keynes: 3 motives for holding money — Transaction (T), Precautionary (P), Speculative (S)
- Transaction motive: daily expenses — income motive (individuals) + business motive (firms)
- Precautionary motive: unexpected emergencies — illness, accidents, unemployment
- Speculative motive: profit from expected changes in bond prices / interest rates
- Bond prices and interest rates: INVERSELY related (Keynes’ key insight)
- Higher interest rate → LOWER speculative demand for money | Lower rate → HIGHER demand
- Keynes: it’s NOT interest that equalizes S=I, but CHANGES IN INCOME
- Keynes explained interest in terms of purely MONETARY forces (not real forces)
- IS Curve: derived from Classical Theory — slopes DOWNWARD — Investment-Savings equilibrium
- LM Curve: derived from Keynes’ Theory — slopes UPWARD — Liquidity-Money supply equilibrium
- IS-LM: Hicks-Hansen synthesis — intersection = equilibrium interest rate AND income
- LM stands for: Liquidity preference and Money supply equilibrium (NOT ‘Liquidity Model’!)
- IS curve derived from Classical theory | LM curve derived from Keynesian theory
- Fiscal expansion → IS shifts RIGHT → ↑ interest rate + ↑ income
- Monetary expansion → LM shifts RIGHT → ↓ interest rate + ↑ income
- Money (option d) is the ODD ONE OUT among rent, interest, wages, money — money is NOT a type of income!
📝 Previous Year Questions
Memory Tricks That STICK
Lock every fact permanently
🧠 Trick 1 — Classical vs Keynes
🧠 Trick 2 — TPS Motives
🧠 Trick 3 — IS Direction
🧠 Trick 4 — LM Direction
🧠 Trick 5 — Bond-Interest Inverse
🧠 Trick 6 — LM Full Form
🧠 Trick 7 — Policy Effects on IS-LM
🧠 Trick 8 — 4 Determinants of Interest
Visual Summary — Chapter Map
Entire chapter in one diagram
Flash Revision — Last-Minute Cards
Read these 10 minutes before exam
⚡ Chapter 15 Complete — Theories of Interest
- Interest: one of 4 incomes (rent, wages, profit, interest) — 3 elements: risk + trouble + pure interest
- Classical Theory: interest = savings supply meets investment demand (REAL factors — Marshall/Fisher/Pigou)
- Keynes: interest = reward for parting with LIQUIDITY (MONETARY forces) — Liquidity Preference Theory
- 3 Motives (TPS): Transaction (daily) + Precautionary (emergency) + Speculative (bond profit)
- Bond prices and interest rates: INVERSELY related — seesaw effect
- IS Curve: from Classical — slopes DOWN ↘ — Investment-Savings | Fiscal policy shifts it
- LM Curve: from Keynes — slopes UP ↗ — Liquidity-Money | Monetary policy shifts it
- IS-LM Equilibrium: Hicks-Hansen synthesis — intersection = equilibrium interest rate + income
- LM ≠ ‘Liquidity Model’ — it’s ‘Liquidity preference + Money supply equilibrium’
- Fiscal expansion → IS RIGHT (↑r, ↑Y) | Monetary expansion → LM RIGHT (↓r, ↑Y)
Banky says: “IS goes DOWN, LM goes UP, they CROSS at equilibrium — and RBI shifts LM every MPC meeting!” 🎉📊
You now understand WHY interest rates exist (Classical + Keynes), WHY people hold cash (TPS motives), WHY bond prices move opposite to rates, and HOW IS-LM determines equilibrium. When RBI announces rate changes — you’ll know the theory behind every basis point! 💪💹