You can bring a horse to water but you cannot make it drink. The old saw may well be on the minds of central bankers. They can cut interest rates, reducing the price of credit and making the environment more favourable for banks. But they cannot make banks lend if banks do not want to. Put more technically, they can affect the cost of credit, but not its supply.

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John Authers on central bankers

Ben Bernanke of the Federal Reserve made that point clear this week by asking banks to consider forgiving mortgage debt for those whose mortgages were worth more than their homes. Normally the Fed has more power at its disposal than just to ask banks to change their behaviour.