金融部门

A financial asset 金融资产 is a claim that stores value: money, stocks 股票 (ownership shares), bonds 债券 (loans that pay interest), and bank deposits. Assets trade off liquidity 流动性 (how easily converted to cash), risk, and return. A key inverse relationship: bond prices and interest rates move in opposite directions – when market interest rates rise, existing bonds paying the old, lower rate are worth less, so their price falls.

• The nominal interest rate 名义利率 is the stated rate, not adjusted for inflation.
• The real interest rate 实际利率 is what you actually earn in purchasing power:

Lenders and borrowers care about the real rate. If inflation turns out higher than expected, real rates fall – helping borrowers and hurting lenders.

Worked example. A loan carries a nominal rate of $6\%$ while inflation runs at $2\%$. The real rate is $6\%-2\%=4\%$, so the lender's purchasing power grows by $4\%$. If inflation instead jumped to $7\%$, the real rate would be $-1\%$ – the lender would actually lose purchasing power.

Money 货币 is anything widely accepted in exchange. Its three functions: a medium of exchange 交换媒介 (avoids barter), a unit of account 记账单位 (a common measure of value), and a store of value 价值储藏 (holds value over time). Modern money is fiat money 法定货币 – valuable because the government declares it legal tender and people trust it, not because it is backed by gold.

Money is measured in tiers by liquidity: M1 (currency plus checkable deposits – the most liquid) and the broader M2 (M1 plus savings deposits and other near-money). Use these AP definitions in exam answers; Fed statistics have counted savings deposits in M1 since May 2020, so published M1 data jump that month. Below M1 is the monetary base 基础货币 (M0, or MB) – currency in circulation plus bank reserves. The money multiplier equals money supply ÷ monetary base, so a central-bank action that raises reserves expands the money supply by a larger amount through the multiplier.

Banks operate on a fractional reserve 部分准备金 system: they keep a fraction of deposits as reserves 准备金 and lend the rest. The fraction they must keep is the required reserve ratio 法定准备金率 (rr). Lending creates new deposits, which are re-deposited and re-lent, expanding the money supply by the money multiplier:

A new $\$1000$ deposit with $rr=0.1$ leaves $\$900$ in excess reserves, so the banking system can expand the money supply by up to $900\times\frac{1}{0.1}=9\,000$. Use a bank's T-account (assets = reserves + loans; liabilities = deposits) to track required reserves and excess reserves 超额准备金 (the amount available to lend).

Worked example. A bank receives a $\$1000$ deposit with $rr=0.20$. It must hold $0.20\times1000=\$200$ as required reserves, leaving $\$800$ of excess reserves to lend. With a money multiplier of $\dfrac{1}{0.20}=5$, that $\$800$ of new lending can expand the money supply by up to $800\times5=\$4000$ across the banking system.

The T-account after a $1000 cash deposit ($rr=0.10$):

The two sides must balance. A single bank can lend only its excess reserves ($900); the banking system as a whole can create up to $900 $\times$ 10 = $9000 of new deposits.

Where the money comes from changes the answer. AP questions test this trap often:

• Cash already in circulation is deposited. The $1000 was already counted in M1 as currency, so the deposit itself does not change the money supply. Only the lending adds money: maximum change $=\$900\times10=\$9000$.
• The Fed buys $1000 of bonds from a bank. The bank swaps bonds for $1000 of reserves, all of them excess. Maximum change in the money supply $=\$1000\times10=\$10\,000$.
• The Fed buys $1000 of bonds from a household, which deposits the payment. The new deposit is new money (+$1000 at once), and banks can lend the $900 of excess reserves (+$9000). Total maximum change $=\$10\,000$.

The multiplier gives a maximum: the real change is smaller if banks keep extra reserves or people hold some of their loans as cash.

In practice. The Federal Reserve cut the required reserve ratio to zero in March 2020, and it has stayed there. The simple money multiplier is still on the AP exam, but in the real U.S. economy the Fed now controls short-term interest rates mainly through the interest it pays on reserves (see Monetary Policy below).

Exam skill: given a required reserve ratio and a deposit, compute excess reserves, the money multiplier, and the maximum change in the money supply.

The money market 货币市场 determines the nominal interest rate:

• Money demand 货币需求 slopes downward against the interest rate – the rate is the opportunity cost of holding money instead of interest-bearing assets. It shifts right with a higher price level or more real GDP.
• Money supply 货币供给 is vertical – set by the central bank, independent of the interest rate.

Their intersection sets the equilibrium interest rate. If the central bank increases the money supply, the supply line shifts right and the interest rate falls.

Monetary policy 货币政策 is the central bank's (the Federal Reserve's) use of the money supply to steer the economy, working through the interest rate:

• Expansionary (easy) 扩张性: increase the money supply $\to$ interest rate falls $\to$ investment and consumption rise $\to$ AD shifts right (fights recession).
• Contractionary (tight) 紧缩性: decrease the money supply $\to$ interest rate rises $\to$ AD shifts left (fights inflation).

Tools: open-market operations 公开市场操作 (buying bonds injects money, selling bonds withdraws it – the main tool), changing the reserve requirement, and changing the discount rate 贴现率 (the rate banks pay to borrow from the central bank). Follow the full chain on the exam: money supply $\to$ interest rate $\to$ investment $\to$ AD $\to$ output, price level, unemployment.

Modern central banks run an ample-reserves system. Rather than nudging the money supply, the Fed sets administered rates – chiefly the interest on reserves (IOR) 准备金利息 it pays banks – and this steers the policy rate 政策利率 (the federal funds rate, the overnight rate banks charge one another). In the reserve market, reserve demand slopes downward while the central bank supplies reserves at its chosen rate; raising IOR lifts the whole policy rate to fight inflation, lowering it eases to fight recession. (In the older limited-reserves system the Fed instead shifted the reserve supply through open-market operations.)

Banks will not lend reserves to each other for less than the Fed pays them to hold reserves, so IOR acts as a floor under the policy rate. With ample reserves the supply line cuts the flat part of demand, and a small change in the quantity of reserves hardly moves the rate. That is why the Fed moves IOR instead.

A real example. To fight inflation that peaked at 9.1 % in June 2022, the Fed raised its target range for the federal funds rate from near zero in early 2022 to 5.25–5.50 % by July 2023, the fastest rise in four decades. Mortgage rates more than doubled, house sales fell and inflation came down to about 3 % by mid-2024. As inflation slowed, the Fed began cutting in September 2024.

Worked FRQ: monetary policy. Assume an economy is in a short-run equilibrium with an inflationary gap. The central bank operates with ample reserves.

1. Identify an action the central bank can take to close the gap. Raise the interest on reserves (IOR). (In a limited-reserves question: sell bonds through open-market operations.)
2. What happens to the policy rate? It rises.
3. Explain how this affects real GDP. A higher interest rate makes borrowing dearer, so investment and interest-sensitive consumption fall. AD shifts left, so real GDP falls back towards full employment and the price level falls (or rises more slowly).
4. Draw the money market with the policy. Money supply shifts left, so the nominal interest rate rises. (Use the money-market graph above, shifted the other way.)

Write every link of the chain. "The Fed raises rates so inflation falls" loses the explanation mark; "higher rates reduce investment, AD shifts left, so the price level falls" earns it.

The loanable funds market 可贷资金市场 determines the real interest rate and connects saving to investment:

• Supply of loanable funds comes from saving and slopes upward.
• Demand for loanable funds comes from borrowers (firms investing, government borrowing) and slopes downward.

That saving is the economy's national savings 国民储蓄 = private savings (households and firms) + public savings (the government's budget balance – a surplus adds to saving, a deficit subtracts from it). For an open economy, investment = national savings + net capital inflow from abroad. So a bigger budget deficit is negative public saving that shrinks the supply of loanable funds and crowds out investment.

More saving shifts supply right and lowers the real rate; more government borrowing shifts demand right and raises the real rate – the mechanism behind crowding out. Distinguish the two graphs: the money market sets the nominal rate (vertical money supply), while loanable funds sets the real rate (upward-sloping saving supply).

What shifts which curve.

Exam skill: know which graph to draw – money market for monetary policy, loanable funds for saving, deficits, and crowding out – and trace how a shift in one feeds into AD-AS.

• Know money's three functions and the M1/M2 measures.
• The money market sets the nominal interest rate (vertical money supply); more money supply lowers the rate.
• Compute the money multiplier $\tfrac{1}{rr}$ and the maximum change in the money supply from a new deposit.
• Trace monetary policy: money supply → interest rate → investment → AD → output.
• Distinguish the money market (nominal rate) from the loanable-funds market (real rate); use the real rate $=$ nominal $-$ inflation.