Japan's yen intervention is a symptom. The disease is policy

THE LATEST episode in the yen's long decline has a historic twist. On July 30th Japan's finance ministry sold dollars to buy yen, pulling the currency from its four-decade low. The following day, the American treasury department joined in with outright purchases of its own, executed through the Federal Reserve Bank of New York. It was a historic intervention, and coordination of this sort between the two countries is tightening to a degree unseen in decades. Mr Scott Bessent, the treasury secretary, added verbal support, declaring the currency "very undervalued". And it makes the real problem harder to miss.

The yen has fallen to around 163 per dollar this year. That is not merely a number on a screen. A weak yen makes imported energy, food and raw materials more expensive for a country that relies on foreign suppliers for most of what it burns and eats. It raises costs for households, distorts inflation, and pushes wages into a catch-up game that Japan's economy is poorly equipped to win. The intervention on Thursday briefly reversed the slide, as Japan's estimated $53bn of yen purchases lifted the currency as much as 3.3% in New York trading. But currency markets trade $9.5tn a day. A one-off splash of $53bn can move a price; it cannot rewrite the incentives that set it.

Those incentives are structural. The yen is depressed by a gap in interest rates. The Bank of Japan's policy rate is 1%. The Federal Reserve's target range sits at 3.5% to 3.75%. The difference of roughly 250-275 basis points fuels the yen carry trade, a strategy in which investors borrow cheaply in yen and reinvest in higher-yielding dollar assets. It is a mechanical force that operates every trading day, amplified by leverage and algorithmic flows. Buying yen at a point in time is like tapping the brake while keeping the accelerator pressed to the floor.

Japan's government is the one with its foot on the accelerator. Prime Minister Sanae Takaichi's fiscal programme is expansive in a way that markets are unlikely to forgive. Her administration is preparing to cut the sales tax on food from 8% to 1% for two years. A full reduction in the tax on food to zero would cost roughly ¥5tn ($31bn) a year, according to the finance ministry, and there is no clear plan for how to fund even the temporary cut. Ms Takaichi is also pushing an unprecedented ¥370tn ($2.3tr) domestic investment plan and a steep increase in defence spending, all while Japan's public debt exceeds 250% of GDP. Fiscal expansion of this scale widens the interest-rate gap between Tokyo and Washington, because it makes investors less confident that the Bank of Japan can raise rates aggressively without straining government finances.

This is where the Bank of Japan is trapped. On July 31st the central bank held rates at 1% by an 8-1 vote, with board member Hajime Takata dissenting and proposing a hike to 1.25%. The BOJ's governing council was expected to upgrade its growth forecast and cut its inflation estimate, but Governor Kazuo Ueda signalled readiness to tighten further. The constraint is clear: core consumer inflation is 1.6%, below the BOJ's 2% target, and a dovish Takaichi administration is unlikely to welcome a central bank that accelerates hikes and risks a recession. The BOJ is expected to raise rates roughly once every six months, which is too slow to close a quarter-century's worth of divergence with the Fed.

American cooperation, for all its novelty, cannot bridge the gap. The US Treasury's intervention was historic, but it is also a one-off. Mr Bessent, who cut his teeth on currency bets at a hedge fund, understands markets better than most politicians. Yet the American treasury has no mandate to manage the yen's level, and selling foreign reserves to buy Japanese currency is not a sustainable strategy for either country. Moreover, Japan's intervention involves liquidating dollar assets, potentially including US Treasuries, which would push American yields higher at a moment when Washington is already concerned about borrowing costs. US support is real but bounded.

To be sure, the yen's weakness is not entirely Japan's fault. The dollar's strength reflects America's own policy choices, including tariffs and fiscal stimulus that have pushed growth and inflation above the Fed's comfort zone. The Fed held rates at its July meeting, but three members dissented in favour of a hike. Middle East tensions keep oil prices jumpy, and global risk sentiment flows disproportionately into the dollar. No single country can cure a strong dollar on its own.

But the deeper problem in Japan is not the dollar. It is the contradiction between fiscal ambition and monetary restraint. Ms Takaichi's programme aims to revive a stagnant economy through domestic investment and populist tax cuts. That is politically understandable. Economically, it is self-defeating. Expanding the deficit while the currency collapses imports more inflation, which forces the central bank to tighten, which raises borrowing costs on the very government bonds that finance the expansion. The policy mix is a feedback loop, and the yen is its early-warning signal.

The better answer is not more intervention. It is fiscal discipline paired with a clearer monetary path. The Takaichi administration should narrow its investment plan to projects that raise productivity rather than subsidise consumption. The food-tax cut, however popular, would be better replaced with targeted support for low-income households, which achieves the same social aim at a fraction of the cost. And the BOJ, having finally escaped its decades-long embrace of zero rates, should resist pressure to crawl forward at a glacial pace. A faster tightening trajectory would signal to markets that Japan is serious about anchoring inflation, and the yen would eventually follow.

Intervention can buy time. It cannot buy consistency. If Japan wants a stronger yen, it needs policies that make one plausible.