In the FT, Martin Wolf discusses Mervyn King’s proposal to make the central bank a “pawnbroker for all seasons” as laid out in King’s recent book “The End of Alchemy.”

Lord King offers a novel alternative. Central banks would still act as lenders of last resort. But they would no longer be forced to lend against virtually any asset, since that very possibility must create moral hazard. Instead, they would agree the terms on which they would lend against assets in a crisis, including relevant haircuts, in advance. The size of these haircuts would be a “tax on alchemy”. They would be set at tough levels and could not be altered in a crisis. The central bank would have become a “pawnbroker for all seasons”.

The key part of this quote is “could not be altered in a crisis.” Central banks and governments have always found it very difficult to commit not to support systemically (or politically) important players ex post. This problem lies at the heart of many problems in the financial system and elsewhere. By assuming that central banks could commit under the proposed arrangement, the proposal abstracts from a key friction.