Every country would like three things at once: a stable exchange rate, a central bank free to set interest rates for the domestic economy, and capital that moves freely in and out. International economics has a blunt answer, known as the impossible trinity or the trilemma: a country can have any two of the three, never all of them at the same time.

The idea comes from the Mundell-Fleming model of the 1960s, and it is one of the most reliable results in macroeconomics. For a company operating across borders it is also a practical tool. The corner a country chooses decides which kind of financial risk the business will face there, and when a country tries to hold all three, it predicts the crisis.

Pick two

The impossible trinity: a fixed exchange rate, independent monetary policy and free capital flows. Each side of the triangle is a feasible regime that gives up the opposite corner, with examples.
  • Fixed rate and free capital, no monetary independence. Hong Kong has pegged its dollar to the US dollar through a currency board since 1983; its interest rates follow those of the Federal Reserve, whatever the local economy needs. The members of the euro area made the same choice among themselves.
  • Free capital and monetary independence, floating rate. The United States, the United Kingdom, Japan, and most inflation-targeting emerging markets such as Chile, Brazil and Mexico. The central bank sets rates for the domestic economy and the currency absorbs the shocks.
  • Fixed rate and monetary independence, controlled capital. China for most of its recent history, and many smaller economies. The peg and the domestic interest rate can coexist only because money cannot leave freely.

What each corner means for a company

The regime does not remove risk; it changes its shape. Treasury and FP&A should plan for the risk the regime creates, not the one it suppresses.

  • Floating rate: continuous currency volatility, but it is visible, priced in the market and hedgeable. Budgets need ranges, and prices need a pass-through policy.
  • Credible peg with free capital: little currency risk, but interest rates are imported. A company can face high rates in a domestic slowdown, or cheap money in a boom, and its financing plan must expect it.
  • Peg with capital controls: the exchange rate looks stable, but the risk moves to convertibility. Dividends may be trapped, imports may wait for dollars, and a parallel market rate may appear. The official rate in the budget becomes a fiction long before it changes.

When a country tries to have all three

Crises happen at the point where a government tries to escape the trilemma: it keeps the peg, keeps rates low to support growth, and lets capital move. Money leaves, the central bank sells reserves to defend the rate, and the market watches the reserves fall. The pattern was visible in Mexico in 1994, in Thailand in 1997, in Argentina in 2001 and, more slowly, in countries that held a peg while financing deficits with reserves.

A peg defended with reserves: as international reserves fall, the premium of the parallel market over the official rate rises, until the peg breaks. Illustrative pattern.

For a company, the signals are measurable long before the devaluation: reserves falling in months of imports, a gap opening between the official and the parallel rate, longer waits for foreign currency, new restrictions on transfers. Each one is a reason to shorten foreign-currency exposures, prepay critical imports, repatriate cash while it is possible and prepare prices for the new rate.
BS

Bartor S.

Founder

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