Eighteenth-century thinkers, such as David Hume and Adam Smith, understood the relationship between the amount of money in circulation and the prices at which goods and services were bought and sold: 'if we consider any kingdom by itself, it is evident, that the greater or less plenty of money is of no consequence, since the prices of commodities are always proportioned to the plenty of money'. In the long run, more money means higher prices. The quantity theory of money, later refined and popularised by the American economists Irving Fisher and Milton Friedman, had been born.

[...] Prices and wages do not adjust instantaneously to clear markets whenever demand and supply are out of balance. Firms change price only irregularly in response to changes in demand; wages adjust only slowly as labour market conditions alter; and expectations are updated only slowly as new information is received. Such 'frictions' or 'rigidities' introduce time lags into the process by which changes in money lead to changes in prices. These lags in the adjustment of prices and wages to changes in demand--so-called 'nominal rigidities'--and lags in the adjustment of expectations to changes in inflation--'expectational rigidities'--generate short-run relationships between money, activity, and inflation. [...]

[...] But if the assets have genuinely lost value, then the central bank must be careful not to subsidise insolvent undertakings. [...]