For unreconstructed efficient market theorists, bubbles do not exist. For semi-reconstructed ones, they exist but, as former Federal Reserve chairman Alan Greenspan claimed in the late 1990s, they are perceptible only after the fact. To spot a bubble in advance, he declared, requires a judgment that hundreds of thousands of informed investors have it all wrong.

Given that many spotted the dotcom bubble in advance and identified the property bubble before the credit crunch of 2007, the semi-reconstructed position seems almost as eccentric as the out-and-out efficient market stance. The eccentricity is further underlined by the fact that 2015 has witnessed two of the most readily detected bubbles in history.

First, China. In the 12 months to its peak on June 12, the Shanghai Composite index rose more than 130 per cent. This happened when expectations of growth in gross domestic product were being revised down and the corporate sector was being squeezed. This was partly a matter of over-investment in real estate and in sectors where surplus capacity was endemic.