History is replete with famous intellectual battles. In the natural sciences, these have usually led to decisive victories, with good science ousting bad. There are few Ptolemaic astronomers left, or believers in the phlogiston theory of combustion. In the social sciences, the situation is different. There have been famous battles galore, but no decisive victories. Indeed, it is characteristic of the social sciences that their battles are interminable, temporary defeats being followed by the regrouping of the defeated forces for a renewed assault.

That economics is not a natural science is clear from the inconclusive engagements that have punctuated its own history. A hundred years ago the classical theory reigned supreme. This “proved” that free markets were automatically self-adjusting to full employment. They were either continually at full employment or, if disturbed by an outside shock, rapidly returned to it. The only thing capable of wrecking the workings of the market’s invisible hand was the visible hand of government interference.