The Bank of Japan (BoJ) stunned the financial markets by unexpectedly expanding its programme of quantitative easing. The bank’s existing measures, a “different dimension” of easing from past efforts, were already daringly bold. Now it will swell Japan’s monetary base at an even faster pace, by around ¥80 trillion ($712 billion) each year, up from ¥60 trillion-70 trillion currently. To do so, it will hoover up still larger quantities of Japanese government bonds (JGBs).

The bank’s action is also an admission of partial failure thus far. Its bond-buying has succeeded in sparking some inflation, yet its goal of achieving price rises of 2% a year by around April 2015 remains a distant possibility. Along with the government, it badly underestimated the dampening effect of a hike in the consumption tax in April this year, which caused the economy to shrink by 1.7% in the second quarter.

Economists had started to question Mr Kuroda’s oft-stated commitment to banishing Japan’s entrenched deflationary psychology. Mr Kuroda admitted that matters had reached a “critical point”, as the bank’s efforts were losing momentum.

Now a fresh round of no-holds-barred QE will immediately boost Mr Abe’s economic plan. The Nikkei stock index—a vital gauge of success for the government—rose to its highest level in seven years on the news. The yen lurched further downwards, which will help import inflation.

As well as buying an additional ¥30 trillion of JGBs a year, the BoJ will also purchase more risky assets in the form of exchange-traded funds and investment trusts in Japanese property.

A motivation for Mr Kuroda—in addition to visibly slowing inflation and weak growth—may have been an intensifying political debate over whether or not Mr Abe should again raise the unpopular consumption tax from 8% to 10% in 2015.

But this latest round of QE is not without its detractors. In April 2013 the BoJ’s nine-strong policy board voted unanimously in favour of its radical new monetary drive, this time it revealed a rare split.