The Death of the Trilemma: Why Floating Rates Won't Save You

If you took Macroeconomics 101, you saw the triangle. The Mundell-Fleming Trilemma states that a country can only choose two of the following three policy options:

1. Fixed Exchange Rate: Pegging your currency to another (like the DKK/EUR peg).

2. Free Capital Movement: Allowing money to flow in and out freely.

3. Independent Monetary Policy: Setting your own interest rates to manage inflation/unemployment.

The Old Consensus

The standard view was simple: If you want independent monetary policy and free capital flows (like the UK or Sweden), you must have a floating exchange rate. The exchange rate acts as a shock absorber. If capital flees, the currency depreciates, boosting exports and stabilizing the economy.

This is why the Eurozone crisis was so hard for Greece (no currency to devalue) but easier for the UK.

Enter Hélène Rey (2013)

In her seminal Jackson Hole paper, French economist Hélène Rey dropped a bomb on this consensus. She argued that the Global Financial Cycle (driven largely by US monetary policy and risk appetite) is so powerful that it overwhelms the shock-absorbing capacity of floating exchange rates.

$$\text{Trilemma} \rightarrow \text{Dilemma}$$

Rey's conclusion? "Independent monetary policies are possible if and only if the capital account is managed."

Why the Float Fails

When the US Federal Reserve raises rates, the VIX (risk aversion) tends to rise. Global banks, which borrow in dollars to lend globally, shrink their balance sheets. Credit contracts everywhere—in Brazil, Korea, and the UK—regardless of their exchange rate regime.

So, even if you float your currency, you import the Fed's monetary stance. If you try to lower rates while the Fed hikes, capital flight will be so severe that it threatens financial stability, forcing you to hike anyway.

The New Reality

This transforms the Trilemma into a Dilemma: You can have independent policy or free capital flows. You cannot have both, regardless of your exchange rate.

In Part 2, we will look at the data behind this claim: How the VIX drives global capital flows.