One is monetary policy: the central bank can print money and drive down interest rates.
When central banks print notes and issue credit, they increase the amount of money available in the economy.
The banks print money and use it to buy a bond or debt.
If the central bank simply printed the money, it would have to cope with the resulting increase in purchasing power.
The central bank can print new yen in order to buy lots of assets, from commercial paper to foreign exchange.
Second, banks print money - they don't merely borrow it.
In the early 1800s, some banks printed their own paper money in Australia.
The central bank has been printing yuan on a vast scale to buy dollars and prevent its appreciation.
Rates are already near to zero and central banks have already been 'printing money'.
The banks then could print banknotes worth up to 90% of the value of the bonds.