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The exchange rate is the price of one currency in terms of another. Exchange rate systems determine how this price is set — whether by market forces, by government intervention, or by a combination of both. The choice of system is one of the most consequential decisions a country makes, because it shapes the credibility of its monetary policy, its exposure to external shocks, and the stability of its trade. This lesson examines the three main systems (floating, fixed, managed float), the precise vocabulary of depreciation/appreciation versus devaluation/revaluation, the mechanics of defending a peg, and the trade-offs between the systems — including the Marshall-Lerner condition, the J-curve and the policy trilemma that constrains every choice.
This lesson addresses AQA A-Level Economics (7136), section 4.2.6 — The international economy: exchange rate systems (floating, fixed, managed), and government intervention in currency markets.
Assessment objectives in play:
Key Definition: The exchange rate is the rate at which one currency can be exchanged for another. For example, if £1 = $1.25, one pound sterling buys 1.25 US dollars.
A rise in the exchange rate (appreciation/revaluation) makes the currency more expensive — each unit buys more foreign currency. A fall (depreciation/devaluation) makes it cheaper. The terminology depends on the system:
| Term | Meaning | System |
|---|---|---|
| Appreciation | Currency rises in value via market forces | Floating / managed |
| Depreciation | Currency falls in value via market forces | Floating / managed |
| Revaluation | Authorities raise the official peg | Fixed |
| Devaluation | Authorities lower the official peg | Fixed |
Exam Tip: Use "appreciation/depreciation" for market-driven moves under a floating rate, and "revaluation/devaluation" for deliberate policy changes to a peg. Mixing these is one of the most common—and avoidable—errors in this topic.
There is a further point of precision worth mastering. The exchange rate is a price, and like any price it can be quoted in two directions: £1 = $1.25 is the same information as $1 = £0.80. Always be clear which currency you are pricing, because "the pound rises" and "the dollar falls" can describe the same event. When a question gives a rate, decide first which currency is the "good" being priced (here, the pound, priced in dollars), so that an appreciation unambiguously means the pound buys more dollars. Exchange rates can also be expressed as a trade-weighted (effective) index against a basket of partner currencies, which is a better guide to overall competitiveness than any single bilateral rate, since a currency can rise against one partner while falling against another.
The effects of a falling currency are summarised by the WPIDEC / SPICED logic — a Weaker Pound means Imports Dearer, Exports Cheaper; a Stronger Pound means Imports Cheaper, Exports Dearer:
flowchart LR
A[Pound depreciates] --> B[Exports cheaper<br/>in foreign currency]
A --> C[Imports dearer<br/>in domestic currency]
B --> D[Export volume rises]
C --> E[Import volume falls + import<br/>prices push up inflation]
D --> F[Net trade / current<br/>account may improve<br/>if Marshall-Lerner holds]
E --> F
Under a freely floating system the currency's value is set entirely by supply and demand in the foreign-exchange market, with no government intervention. The rate moves continuously to clear the market, so there is never a "shortage" or "surplus" of the currency at the going price — the price simply adjusts.
The headline advantages of a float all flow from the rate being free to move. Automatic adjustment is the classic case: a current-account deficit means more of the currency is being supplied (to buy imports) than demanded, so the rate falls, making exports cheaper and imports dearer and tending to correct the deficit without any policy action — though, as the Marshall-Lerner condition shows, this self-correction is not guaranteed. Because the central bank is not committed to defending any particular rate, it enjoys full monetary-policy independence: interest rates can be set to hit the domestic inflation target or support growth, which is why most large advanced economies float. A float also requires no large foreign-currency reserves, freeing resources that a pegging country must tie up, and it lets the rate continuously reflect fundamentals such as relative productivity, inflation and interest rates.
| Advantage | Explanation |
|---|---|
| Automatic adjustment | A current-account deficit raises the supply of the currency, causing depreciation that makes exports cheaper and imports dearer — self-correcting |
| Monetary-policy independence | Interest rates can target domestic objectives (inflation, growth), not the exchange rate |
| No need for large reserves | No requirement to buy/sell currency to defend a peg |
| Reflects fundamentals | The rate adjusts to relative productivity, inflation and interest rates |
The same freedom that gives a float its benefits also creates its weaknesses. Volatility and uncertainty are the most important: a freely floating rate can swing substantially over short periods, raising the risk faced by exporters, importers and investors and potentially deterring trade and FDI — especially harmful for a small, trade-dependent economy. Much of this volatility is driven by speculation and overshooting: because financial markets adjust far faster than goods markets (the Dornbusch insight), short-term capital flows can push the rate well away from its fundamental value before it settles. A depreciating currency also generates imported inflation — dearer imports and imported inputs feed cost-push pressure into the domestic price level, which can be destabilising for an economy already prone to inflation. Finally, a float may not correct external imbalances at all: if the economy's trade is price-inelastic, a depreciation can worsen the trade balance rather than improve it, as the Marshall-Lerner condition makes precise.
| Disadvantage | Explanation |
|---|---|
| Volatility and uncertainty | Fluctuations raise risk for traders and investors, deterring trade and FDI |
| Speculation / overshooting | Short-term capital flows can push the rate away from fundamentals |
| Imported inflation | Depreciation raises import prices, feeding into domestic inflation (cost-push) |
| May not correct imbalances | If trade is price-inelastic, depreciation can worsen the balance (Marshall-Lerner) |
Under a fixed (pegged) system the authorities peg the currency at a chosen rate against another currency or a basket, and intervene to hold it there.
Maintaining a fixed rate is not passive — the authorities must continuously stand ready to offset any market pressure that would move the rate away from the peg, using a combination of three tools:
The diagram shows a central bank defending a floor: market supply has risen (S to S2), which would push the rate down to e2, so the bank buys currency, adding demand (D to D2) to hold the rate at the peg.
Advantages. The central benefit is certainty and stability: with the exchange rate fixed, exporters, importers and investors face no currency risk, which lowers the cost of trade and encourages long-term FDI — particularly valuable for a small, open economy whose firms cannot easily hedge currency exposure. A fixed rate also imposes anti-inflationary discipline: because the nominal rate cannot adjust, a country must keep its inflation in line with the anchor currency or lose competitiveness, so the peg acts as a credible nominal anchor that can break an inflationary psychology far faster than domestic promises alone. Finally, a system of fixed rates prevents competitive (beggar-thy-neighbour) devaluation, in which countries try to gain a trade advantage by weakening their currencies — a destructive dynamic that fixed regimes are designed to avoid.
Disadvantages. The price of these benefits is the loss of monetary-policy independence: interest rates must be set to defend the peg, not to manage domestic demand, so the central bank cannot cut rates to fight a recession or raise them freely to cool a boom. A peg also requires large foreign-currency reserves to fund intervention, which is costly to hold. It is vulnerable to speculative attack: if markets come to believe the peg is misaligned, one-way bets against the currency can overwhelm even large reserves (Black Wednesday 1992; the 1997 Asian financial crisis), forcing a humiliating and abrupt devaluation. And because the rate is fixed rather than adjusting to fundamentals, a peg can become misaligned — set too high or too low relative to the rate the market would set — causing persistent current-account surpluses or deficits and the build-up of the very pressures that eventually trigger a crisis.
Most economies today operate a managed float (sometimes called a "dirty float"): the rate is primarily market-determined, but the central bank intervenes occasionally to smooth excessive volatility or resist movements it judges undesirable. The managed float is best seen as a spectrum between the two pure systems — countries differ in how heavily and how openly they intervene.
The trade-off is that a managed float blurs the trilemma rather than escaping it: the more a central bank intervenes to control the rate, the more its monetary policy becomes constrained by the exchange-rate objective, edging back toward the fixed-rate end of the spectrum. Heavily managed regimes can also attract accusations of currency manipulation if a country is seen to hold its rate artificially low to boost exports.
Exam Tip: Very few economies are purely floating or purely fixed. Most are managed floats. China is a useful example — the People's Bank of China manages the yuan within a band rather than letting it float freely, which is why the managed float is so often the right "realistic compromise" to offer in an evaluation.
Key Definition: The Marshall-Lerner condition states that a depreciation/devaluation improves the trade balance only if the sum of the (absolute) price elasticities of demand for exports and imports exceeds one.
∣PEDX∣+∣PEDM∣>1
When the currency falls, exports get cheaper in foreign-currency terms and imports get dearer in domestic-currency terms. The price effect and the quantity effect pull in opposite directions on the trade balance, and which dominates depends on elasticities. If demand is elastic, the quantity responses (more exports sold, fewer imports bought) outweigh the adverse price effect and the trade balance improves. If demand is inelastic, the balance can worsen: the country pays more for a barely-reduced volume of imports while earning little extra from a barely-increased volume of exports.
Intuitively, a depreciation raises the domestic-currency cost of every imported unit immediately. Unless import volumes fall enough (elastic import demand) and export volumes rise enough (elastic foreign demand for exports) to offset that, the import bill rises faster than export earnings and the balance deteriorates. Summing the two elasticities captures the combined responsiveness on both sides of the trade account; the threshold of one is the point at which the favourable quantity effects exactly offset the unfavourable price effect.
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