The Quantity Theory of Money | 货币数量论

📚 The Quantity Theory of Money | 货币数量论

In macroeconomics, the quantity theory of money links the money supply to the price level. It argues that, other things being equal, a rise in the money supply causes a proportional rise in the average price level, leaving real output and employment unchanged in the long run.

在宏观经济学中，货币数量论将货币供给与价格水平联系起来。该理论认为，在其他条件不变时，货币供给增加会导致平均价格水平同比例上升，长期内实际产出和就业不变。

1. The Core Claim of the Quantity Theory | 货币数量论的核心主张

The quantity theory of money is a classical explanation of the general price level. It claims that the price level is determined mainly by the quantity of money in circulation. When the central bank increases the nominal money supply, the extra money is spent on the same volume of real goods and services, so prices are bid up.

货币数量论是古典经济学对一般价格水平的解释。它认为价格水平主要由流通中的货币数量决定。当中央银行增加名义货币供给时，额外的货币会追逐同样数量的实际商品和服务，从而推高价格。

This theory treats money primarily as a medium of exchange, not as a store of value that can persistently raise real wealth. Therefore, holding more money than people want leads them to spend it, increasing nominal aggregate demand.

该理论主要把货币视为交易媒介，而不是能够持续增加实际财富的价值储藏手段。因此，人们持有的货币超过意愿时，就会增加支出，从而提高名义总需求。

2. The Equation of Exchange | 交易方程式

The quantity theory is often expressed through the equation of exchange, an identity from Irving Fisher.

货币数量论通常通过欧文·费雪提出的交易方程式来表达。

M × V ≡ P × T

Here M is the nominal money supply, V is the velocity of circulation, P is the average price level, and T is the volume of transactions or real output. The equation is an identity because total spending on goods and services must equal total receipts.

其中 M 表示名义货币供给，V 表示货币流通速度，P 表示平均价格水平，T 表示交易量或实际产出。该方程是一个恒等式，因为对商品和服务的总支出必然等于总收入。

As a theory, it adds behavioural assumptions to the identity. Fisher argued that V and T are relatively stable in the long run, so changes in M pass directly into P. This turns an identity into a causal theory of inflation.

作为理论，它为恒等式加入了行为假设。费雪认为 V 和 T 在长期内相对稳定，因此 M 的变化会直接传导到 P。这使恒等式变成了通货膨胀的因果理论。

3. Fisher’s Transactions Approach | 费雪的交易分析法

Fisher’s version focuses on money used for transactions. He assumed that the velocity of circulation is determined by payment habits, financial institutions and technology, which change slowly. In the short run, V can be treated as constant.

费雪的版本关注用于交易的货币。他假设流通速度由支付习惯、金融机构和技术决定，这些因素变化缓慢。在短期内，V 可以视为常数。

Fisher also assumed that the economy normally operates near full employment. Hence T, the number of transactions or real output, cannot rise quickly just because more money is available. With V and T fixed, an increase in M must raise P proportionally.

费雪还假设经济通常在充分就业附近运行。因此，交易数量或实际产出 T 不会仅仅因为货币增加而迅速上升。在 V 和 T 不变的情况下，M 的增加必然使 P 同比例上升。

P = (M × V) ÷ T

This expression shows the direct link: if M doubles while V and T remain unchanged, P doubles.

这个表达式显示了直接联系：如果 M 翻倍而 V 和 T 不变，P 也会翻倍。

4. The Cambridge Cash-Balance Approach | 剑桥现金余额分析法

The Cambridge economists, including Marshall and Pigou, developed a slightly different version. They asked how much money people wish to hold as a fraction of their nominal income.

剑桥学派经济学家，包括马歇尔和庇古，提出了略有不同的版本。他们关注人们希望以名义收入的多大比例持有货币。

Md = k × P × Y

In this equation, Md is the demand for money balances, P is the price level, Y is real national income, and k is the fraction of nominal income held as money. In equilibrium, money demand equals money supply, so M = kPY.

在这个方程中，Md 表示货币余额需求，P 表示价格水平，Y 表示实际国民收入，k 表示以货币形式持有的名义收入比例。在均衡状态下，货币需求等于货币供给，因此 M = kPY。

The Cambridge k is the reciprocal of Fisher’s V. If people hold a smaller fraction of income as money, they spend each unit of money more frequently, so velocity rises.

剑桥 k 是费雪 V 的倒数。如果人们以货币形式持有收入的比例较小，每单位货币的使用频率就会提高，因此流通速度上升。

k = 1 ÷ V

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