Some of these nuggets are much larger and more instantly recognisable than others. His December 1996 speech, for example, which questioned whether share prices were being driven higher in part by “irrational exuberance”, led directly to a 150-point decline in the Dow Jones index the next day.

Yesterday’s speech at the annual Jackson Hole symposium on monetary policy, in the bucolic surroundings of Grand Teton National Park in Wyoming, wasn’t quite in the “irrational exuberance” category of headline-making.

But in a crucial passage of his speech opening the conference, Mr Greenspan pointed to an important evolution in his views as he prepares to leave office early next year.

After the collapse of equity prices in the past five years, attention has focused on US house prices, which have risen sharply. But until now Mr Greenspan has generally disdained the idea of a bubble that could burst with damaging consequences for the broader economy, a fear constantly in the mind of the Bank of England’s policymakers.

He and his economists at the Fed have stressed the differences between America and Britain, noting that housing plays a much bigger role in the UK economy.

In the US, they point out, there has never been a sustained nationwide decline in house prices, largely because the US is a large and diffuse market. There may be areas of “froth”, Mr Greenspan has said, but not much risk of a general downturn in prices.

But yesterday the chairman said that, while good economic reasons — the improved flexibility and efficiency of the US economy — might have made investments in all kinds of assets less risky, there was a danger that investors might have pushed this logic too far, lowering the “risk premium” on such assets. “History has not dealt kindly with the aftermath of protracted periods of low risk premiums,” he said.

None of this means the Fed will start actively targeting the housing market with much higher interest rates; after all, it did little to try to prick the equity bubble in the late 1990s. But it does mean that Mr Greenspan — and presumably his successor — are unlikely to shift from their current path of raising interest rates as long as house prices continue to rise.

Explore Economics

• Autumn Budget 2007

• Budget 2008

• World Economic Forum

• The Times MPC

Times Recommends

• Food prices rise 8.3% on soaring fish and meat
• Car sales crash as economy hits skids
• House prices fall but Bank leaves rates on hold