The Bank of Japan has announced it is to carry out "quantitative and qualitative easing" in an effort to return inflation to its target rate of 2 per cent in "about two years". In a statement, the bank's incoming governor has said:
In order to do so, it will enter a new phase of monetary easing both in terms of quantity and quality. It will double the monetary base and the amounts outstanding of Japanese government bonds (JGBs) as well as exchange-traded funds (ETFs) in two years, and more than double the average remaining maturity of JGB purchases.
The scale of the easing plan is enormous. The bank currently has ¥135trn of outstanding bonds, and plans to increase that to ¥270trn. That's an easing programme of £1.878trn, compared to the Bank of England's asset purchase programme of £375bn over the last few years.
But the "qualitative" aspect of the easing is even more groundbreaking:
In addition, JGBs with all maturities including 40-year bonds will be made eligible for purchase, and the average remaining maturity of the Bank's JGB purchases will be extended from slightly less than three years at present to about seven years – equivalent to the average maturity of the amount outstanding of JGBs issued.
Increasing the money supply by such a monumental amount is a risky move. The classic equation for money, MV=PY, holds that if the (V)elocity of money – the rate at which money changes hands – stays fixed, then an increase in the (M)oney supply must lead to an increase in either the (P )rice level, or output (Y), or both. The BoJ will be hoping for the price level to increase to two per cent and stay there, and for an increase in output to pick up the rest of the money; but once started, inflation can be hard to stop.
At the moment, deflation is Japan's biggest priority, but it runs the risk of jumping from the frying pan to the fire.
Perhaps the most important part of the announcement is what the FT's Kate Mackenzie calls  "Communications and other Jedi matters". It's the bit where the bank attempts to push expectations in the direction they want, without actually saying what they want, because if they say what they want, people will second-guess what they want and then what they want won't actually happen the way they want it to and – look, they just said this:
The quantitative and qualitative monetary easing, introduced by the Bank today, will underpin the Bank’s commitment, and is expected not only to work through such transmission channels like longer-term interest rates and asset prices but also to drastically change the expectations of markets and economic entities.
What does it mean? We'll find out a bit more on the 26th, when the bank meets next.