Central banks have always drawn a line between illiquidity and insolvency. Illiquidity is often viewed as something temporary, an aberration where central bank intervention is permissible. Insolvency, on the other hand, is viewed as something fundamental and abominable and thus to be discouraged. Central bank intervention to restore liquidity to an illiquid market would simply bring prices back to fundamentals. Intervening to bail out insolvent firms would, however, encourage irresponsible behaviour and should be resisted. At least, so the catechism goes.

Central bankers know, though, that the line between illiquidity and insolvency is an extremely fuzzy one, made more so with developments in financial markets. Take, for instance, a mortgage loan made against a house. If the housing market is liquid, loans are easier to come by. The reason is obvious. One of the biggest costs to a lender is that if the borrower defaults, the house has to be repossessed and resold with substantial costs. If, however, houses are selling like hot cakes, then the cost of repossession and resale is likely to be small. Housing loans will appear low risk, the risk premium lenders will charge will be small and housing credit will be plentiful. In turn, this will increase the volume of house sales, increasing liquidity in housing markets. Liquidity thus tends to be self-fulfilling.