The three most familiar economic statistics are all measures of change: inflation, the growth of gross domestic product, and the daily rise or fall in the price of shares. Even so, they do not begin to capture the mad churn of the economy: the growth and bankruptcy of companies; the millions of sackings and hirings, which unemployment statistics barely summarise; the movement of goods and services around the world and the ebb and flow of consumer fads. Under the circumstances, it is strange that economists do not have a satisfactory way of talking about change; yet we do not.

As any undergraduate student of economics knows, both microeconomists and macroeconomists tend to describe change in the same way that an advertisement for washing powder does: “before” and “after”. When oil cost $20 a barrel the economy looked like this; now oil costs $100 a barrel, the economy looks like that. Quite how the process of change occurred – or how quickly – is a problem glossed over in the textbooks and most journals.