When the government borrows a trillion dollars, whose money does it borrow? Yours — the same national pool of savings that a startup wants for its factory and your neighbor wants for her mortgage. One pool, many borrowers: the price that rations it is the real interest rate, and the graph that shows the rationing is the loanable funds market. This is where Lesson 8's crowding-out promise gets its picture, where patience (saving) meets ambition (investment) — and where the AP exam runs its favorite which-market-is-it trap. Money market: nominal rate, Fed moves it. Loanable funds: real rate, savers and borrowers move it. Keep the two graphs in separate rooms and Unit 4 becomes routine.
The loanable funds market brings together savers (suppliers of funds) and borrowers (demanders of funds). Its price is the real interest rate (r) — lenders care about purchasing power, not the number printed on the loan (Fisher, Lesson 4).
Equilibrium r clears the market: total saving = total borrowing (Lesson 1's leakage-injection balance, grown up).
Supply shifts right (r falls) when: households become thriftier at every rate; government runs a surplus; foreign savers pour funds in. Supply shifts left (r rises) when: saving rates fall; capital flees abroad.
Demand shifts right (r rises) when: business optimism/expected returns on capital improve; investment tax credits sweeten projects; the government runs a deficit (borrows more at every rate). Demand shifts left (r falls) when: pessimism shelves projects; deficits shrink.
(Convention note: the AP standard models a government deficit as an increase in the demand for loanable funds. Some textbooks model it as reduced supply — same rate direction. On the exam, shift demand.)
Lesson 8's chain gets its picture: the government runs a large deficit → D_LF shifts right → r rises → private investment (and interest-sensitive consumption) is squeezed out.
Consequences layered by horizon: - Short run: the fiscal stimulus's AD boost is partially offset by falling I. - Long run: less investment today → slower capital accumulation → slower LRAS growth (Lesson 14's growth engine runs on the investment that got crowded out).
The mirror image is worth knowing: a surplus (or higher national saving) shifts supply right, lowers r, and crowds in investment.
| Money market | Loanable funds | |
|---|---|---|
| Y-axis | Nominal interest rate | Real interest rate |
| Vertical curve? | MS vertical (Fed-set) | Neither — both slope |
| Movers | Fed policy (MS); PL & real GDP (MD) | Savers, borrowers, deficits, expectations |
| Question keywords | "Fed buys/sells," "money supply," "IORB" | "saving," "deficit," "investment demand," "foreign inflows" |
If the actor is the central bank, draw the money market. If the actors are savers, businesses, or the Treasury's borrowing, draw loanable funds. In the long run the two rates travel together (real = nominal − expected inflation), but the AP grades you on choosing the right graph for the story told.
Apply It: Which market, which curve, which way? (1) The Fed sells bonds. (2) A tech boom raises expected returns on capital. (3) Congress swings the budget from balance to a large deficit. (4) Household saving rates jump. → (1) money market, MS left, nominal rate ↑. (2) loanable funds, D_LF right, r ↑. (3) loanable funds, D_LF right, r ↑ (crowding out). (4) loanable funds, S_LF right, r ↓.
[GRAPH: Loanable Funds Market — government deficit (crowding out)
X-axis: Quantity of loanable funds
Y-axis: Real interest rate (r)
Curve 1: S_LF, upward-sloping (saving)
Curve 2: D_LF₁, downward-sloping (borrowing)
Equilibrium at (Q₁, r₁)
Shift: government borrows to finance a deficit → D_LF shifts right to D_LF₂ →
new equilibrium (Q₂ > Q₁, r₂ > r₁) → higher real rate squeezes out some
private investment (crowding out)]
[GRAPH: Loanable Funds Market — rise in national saving
X-axis: Quantity of loanable funds
Y-axis: Real interest rate (r)
Curves: D_LF fixed; S_LF₁ shifts right to S_LF₂
New equilibrium: r falls, quantity of funds (and investment) rises —
crowding IN]
AP labeling requirements: y-axis must read real interest rate (the word "real" is graded); both curves slope normally (no vertical supply here — that's the money market's signature); label the shift, arrow, and both equilibrium rates. Crowding-out FRQs typically demand this graph plus one sentence connecting r↑ to I↓.
1. B. Supply = all saving flowing into the pool: private, public (surpluses), foreign. A: the money stock lives in the money market. C: that's demand. D: taxes aren't lending. E: no treasury printing press in this model.
Fix: Savers supply; borrowers demand — write S = saving on the curve if it helps.
2. D. Loanable funds clears at the real rate — savers and borrowers think in purchasing power. A/C: nominal rates are money-market territory. B/E: different variables entirely.
Fix: Loanable funds = real rate; money market = nominal rate — the course's most-graded distinction.
3. A. Better expected returns → more projects worth financing at every rate → D_LF right → r rises (and quantity of funds rises). B/D: saving behavior didn't change. C: backwards. E: private markets move without the Fed.
Fix: Expectations about capital returns are a demand-side shifter.
4. E. Deficits are borrowing: demand right, r up — the crowding-out setup. A: the alternative textbook convention; the AP wants demand. B: shifts, not movements — borrowing rose at every rate. C/D: wrong curve/shape.
Fix: On the AP, deficits → D_LF right. Full stop.
5. C. The mechanism is the rate: deficit → r↑ → private I↓ offsets stimulus. A/B: real phenomena but not crowding out. D: fiscal borrowing doesn't shrink money. E: expectations aren't this mechanism.
Fix: Crowding out has three beats — deficit, higher r, lower I. Recite all three.
6. A. Thrift → S_LF right → r falls → more investment financed (crowding in). B/C/D: wrong curve or direction. E: the rate must fall to absorb the extra saving.
Fix: More saving = supply right = cheaper funds = more investment.
7. E. Central-bank bond sales change the money supply — money market, nominal rate. A/B/C/D: saving, deficits, investment incentives, and foreign inflows are all loanable-funds actors.
Fix: Sort by actor: Fed → money market; savers/borrowers/Treasury borrowing → loanable funds.
8. B. Foreign inflows add saving to the domestic pool: supply right, r down, investment up. A/E: inflows aren't domestic borrowing. C: direction reversed. D: supply never goes vertical here.
Fix: Foreign capital inflows = extra supply of loanable funds.
9. D. A surplus is public saving: supply right, r down, investment crowded in. A/B: that's the deficit story. C: surpluses move the market. E: surpluses raise national saving.
Fix: Surplus = saving = supply right; deficit = borrowing = demand right.
10. C. Crowded-out investment means a smaller future capital stock — potential output (LRAS) grows more slowly. A: money growth isn't involved. B: AD moves are the short-run part. D/E: unrelated.
Fix: Investment is tomorrow's LRAS; crowd it out today, grow slower tomorrow.
11. A. Money market = nominal (opportunity cost of holding cash); loanable funds = real (lenders' purchasing-power return). B/C/D: at least one label wrong. E: those are AD-AS axes.
Fix: Two markets, two axes — nominal for money, real for funds. Tattoo it.
12. D. Demand shifted; supply didn't — the higher r moves savers up along S_LF, so quantity supplied rises. A/C: no supply shift or exit occurred. B: supply slopes upward here. E: fully determined.
Fix: When demand shifts, the other curve answers with a movement along — never its own shift.
13. E. Saving is rate-responsive (higher real returns induce more saving/less current consumption) → upward slope; verticality is the money supply's trait because the Fed fixes that quantity. A/B: savings respond to incentives in both runs in this model. C: horizontal-at-a-rate describes no AP curve here. D: money demand slopes down, it isn't vertical.
Fix: Only one vertical curve exists in Unit 4 — the money supply. Everything in loanable funds slopes.
The country of Belmara has a balanced government budget and its loanable funds market is in equilibrium.
(a) Draw a correctly labeled graph of Belmara's loanable funds market, showing the equilibrium real interest rate r₁ and quantity Q₁.
(b) Belmara's legislature passes a large defense-spending program financed entirely by government borrowing. Show the effect on your graph, labeling the new equilibrium real interest rate r₂.
(c) Explain how the change in the real interest rate from (b) affects private-sector investment spending. What is this effect called?
(d) Explain one way the change in investment from (c) could affect Belmara's long-run aggregate supply.
1. B. Supply = all saving flowing into the pool: private, public (surpluses), foreign. A: the money stock lives in the money market. C: that's demand. D: taxes aren't lending. E: no treasury printing press in this model. Fix: Savers supply; borrowers demand — write S = saving on the curve if it helps.
2. D. Loanable funds clears at the real rate — savers and borrowers think in purchasing power. A/C: nominal rates are money-market territory. B/E: different variables entirely. Fix: Loanable funds = real rate; money market = nominal rate — the course's most-graded distinction.
3. A. Better expected returns → more projects worth financing at every rate → D_LF right → r rises (and quantity of funds rises). B/D: saving behavior didn't change. C: backwards. E: private markets move without the Fed. Fix: Expectations about capital returns are a demand-side shifter.
4. E. Deficits are borrowing: demand right, r up — the crowding-out setup. A: the alternative textbook convention; the AP wants demand. B: shifts, not movements — borrowing rose at every rate. C/D: wrong curve/shape. Fix: On the AP, deficits → D_LF right. Full stop.
5. C. The mechanism is the rate: deficit → r↑ → private I↓ offsets stimulus. A/B: real phenomena but not crowding out. D: fiscal borrowing doesn't shrink money. E: expectations aren't this mechanism. Fix: Crowding out has three beats — deficit, higher r, lower I. Recite all three.
6. A. Thrift → S_LF right → r falls → more investment financed (crowding in). B/C/D: wrong curve or direction. E: the rate must fall to absorb the extra saving. Fix: More saving = supply right = cheaper funds = more investment.
7. E. Central-bank bond sales change the money supply — money market, nominal rate. A/B/C/D: saving, deficits, investment incentives, and foreign inflows are all loanable-funds actors. Fix: Sort by actor: Fed → money market; savers/borrowers/Treasury borrowing → loanable funds.
8. B. Foreign inflows add saving to the domestic pool: supply right, r down, investment up. A/E: inflows aren't domestic borrowing. C: direction reversed. D: supply never goes vertical here. Fix: Foreign capital inflows = extra supply of loanable funds.
9. D. A surplus is public saving: supply right, r down, investment crowded in. A/B: that's the deficit story. C: surpluses move the market. E: surpluses raise national saving. Fix: Surplus = saving = supply right; deficit = borrowing = demand right.
10. C. Crowded-out investment means a smaller future capital stock — potential output (LRAS) grows more slowly. A: money growth isn't involved. B: AD moves are the short-run part. D/E: unrelated. Fix: Investment is tomorrow's LRAS; crowd it out today, grow slower tomorrow.
11. A. Money market = nominal (opportunity cost of holding cash); loanable funds = real (lenders' purchasing-power return). B/C/D: at least one label wrong. E: those are AD-AS axes. Fix: Two markets, two axes — nominal for money, real for funds. Tattoo it.
12. D. Demand shifted; supply didn't — the higher r moves savers up along S_LF, so quantity supplied rises. A/C: no supply shift or exit occurred. B: supply slopes upward here. E: fully determined. Fix: When demand shifts, the other curve answers with a movement along — never its own shift.
13. E. Saving is rate-responsive (higher real returns induce more saving/less current consumption) → upward slope; verticality is the money supply's trait because the Fed fixes that quantity. A/B: savings respond to incentives in both runs in this model. C: horizontal-at-a-rate describes no AP curve here. D: money demand slopes down, it isn't vertical. Fix: Only one vertical curve exists in Unit 4 — the money supply. Everything in loanable funds slopes.
Exam tip: Before drawing anything in Unit 4, ask two questions: Who acted? (Fed → money market; savers/firms/Treasury → loanable funds) and which axis? (nominal vs. real). Those two answers are worth more points than any other five seconds of thought on this exam. Next lesson: Unit 5 opens with the inflation-unemployment tradeoff — the Phillips curve.