It is a decade - 10 years and a week, to be precise - since Alan Greenspan made his celebrated remark about "irrational exuberance". And it is almost two years since the former Fed chairman mused about the "conundrum" of low bond yields and spreads. It is worth recalling the reception given to the first warning for what it might tell us about the second.

The first point about the "irrational exuberance" speech is that in practical market terms it was completely wrong. US equities went on climbing for another three years, in which time the Dow almost doubled and the Nasdaq very nearly quadrupled.