Sometimes markets give governments no choice. Traders judged that last week’s savage sell-off of all world currencies against the yen left the Japanese currency far higher than policymakers could stand.

They heard the G7 announce that it was concerned by volatility in the yen, and heard a clear hint that intervention was possible. They heard Japanese regulators announce that they were bringing forward to this week rules that would make it harder to sell stocks short. They saw reports in the Japanese press that the Bank of Japan could act directly by cutting interest rates on Friday.