Financial encyclopedia

The yen has been declining steadily recently, with the dollar surging past 163 against the yen and falling to around a 40-year low.  
The Japanese government has repeatedly warned it will take decisive action if necessary.  
Yet markets keep asking:  
With the yen already at such lows, why hasn't Japan acted immediately?  
Perhaps it's not that Japan lacks the ability, but rather that in foreign exchange intervention, the key issue has never been merely "whether to intervene," but "when to intervene." 

What is foreign exchange intervention?  
Simply put, "intervening to rescue the yen" means the Japanese government sells dollars and buys yen in the market.  
When there is a sudden surge in large-scale yen buying, the yen can rise sharply in a short period of time. 

But keep in mind:  
Intervention may affect short-term prices, but not necessarily the long-term flow of capital. 

Why doesn't Japan act immediately?  
First, the government may not want the market to know its bottom line.  
If Japan intervenes every time the dollar hits a certain level against the yen, speculators will quickly learn the government's pattern and even anticipate moves in advance.  
Therefore, Japan likely isn't determined to defend any specific level—such as 163, 165, or any other number—but instead wants to preserve the element of surprise, making it impossible for the market to predict when intervention will occur.  
When the market is uncertain about the government's floor, the risk of shorting the yen actually increases. 

Fundamentals remain unchanged, and the impact of intervention may be short-lived.  
This time, the weak yen is not just a short-term speculative move.  
Several underlying factors continue to support the dollar: 

U.S. interest rates remain high,  
while Japanese interest rates are relatively low.  
Geopolitical tensions have increased demand for the dollar as a safe-haven currency.  
Rising oil prices are adding to Japan's import costs.  
If these fundamental factors do not change, even if Japan buys yen, capital may still flow back to the dollar later. 

In other words:  
Intervention can push up the yen, but it may not necessarily hold it.  
This also explains why Japan is reluctant to prematurely deplete its foreign exchange reserves when the odds of success are lowest. 

What the government truly manages may not be the level, but the speed.  
The market often speculates whether Japan will hold at 160, 163, or 165.  
But what the government is really concerned about might not be which specific number the yen stops at, but whether the exchange rate plunges out of control in a short period. 

Because the drop is too steep, it may trigger: 

Speculators collectively rush to sell  
Input costs suddenly rise  
Companies struggle to manage costs  
Household inflation expectations deteriorate  
Market loses confidence in policy  
Therefore, foreign exchange intervention is often not aimed at immediately reversing the trend, but rather at slowing the decline and preventing the market from forming a one-sided expectation that "the yen will keep falling forever." 

What should investors watch for?  
To determine whether Japan will intervene, one should not look only at how high the dollar has risen against the yen.  
Other factors to monitor include: 

Has the yen's decline suddenly accelerated?  
Is there clear one-sided speculation in the market?  
Have Japanese officials escalated their rhetoric?  
Is the U.S. willing to cooperate?  
Have fundamental factors such as the U.S.-Japan interest rate differential and oil prices changed?  
Price movements are merely surface-level; what governments truly care about may be whether the market is beginning to spiral out of control. 

The hardest part of foreign exchange intervention isn't whether there's enough funding, but when to act.  
Japan doesn't necessarily need to defend a specific price level; what it truly wants to prevent is the market's belief that the yen can keep falling indefinitely.  
Governments can intervene in prices, but only fundamentals can truly change the direction.