Economic theorems must reflect what people actually do - not what some abstract theory says they ought to do.
At the most recent turn of the century, a group of French economics students at La Sorbonne organised their own revolt against their teachers, and the way they were teaching economics.
They called it the 'Post-Autistic Economics' campaign. "It was in the beginning a modest initiative, almost confidential," wrote the French newspaper Le Monde in September 2000.
"It has now become a subject of an important debate which has created a state of effervescence in the community of economists. Should not the teaching of economics in universities be re-thought?"
Economics must reconnect with people
The 'post-autistic' campaigners argued that mathematics had "become an end in itself", turning economics into what they called an "autistic science", dominated by abstractions that bore no relation to the real world or to real people.
Within two weeks, the petition calling for re-connection with the real world had 150 signatures, many from France's most important Universities.
Soon newspapers and TV stations all over France had picked up the story and even senior professors were starting a similar petition of their own. The French education minister, Jack Lang, even promised to set up a commission to investigate.
By then, there had also been a vitriolic exchange of articles by French and American economists, a counter-petition launched by the Massachusetts Institute of Technology (MIT); and a peculiar Post-Autistic petition from Cambridge Ph.d students.
What made the petition so peculiar was that the signatories were too frightened for their future careers to put their real names to it.
Moving beyond theorems, to the world as it is
The debate launched by the campaign suggested that economics was really about people, and not just about theorems, and that economists needed to learn from the way people actually behaved so they could see the world as it really is.
Such are the short memories of campaigners that the Post-Autistic Economics Campaign has had be reinvented by economics students more recently, on both sides of the Atlantic - and the basic idea is the same: economics needs to be about the real world.
But then that is what should make economics so fascinating, because - although it is certainly about people - it is also about how people interact, and especially how they interact with money and with each other's values.
Mainstream economics has taken a wrong turning
But the campaign suggested something else as well. It was a shot across the bows of mainstream academic economics, suggesting that it had taken a wrong turning.
It was the central pillar of academic economics that that economics should be a science. But it also seemed to ignore a fundamental tenet of the philosophy of science: that theorems should be subject to the real world.
And in economics specifically, that means that theorems must reflect what people actually do - not what some abstract theory says they ought to do.
Economics: more an ideology than a science
And it needs to be challengeable from below. That is, when a new theory emerges which explains the world better than an existing theory, it needs to be able to replace the old one.
Most of all, it needs to be able to learn from its own history - to go back to roads not taken, ideas not understood at the time, insights suppressed, and take a fresh look at them.
It needs to be able to see the way one thing causes another - and to look into the complexity of the modern world and predict other courses of action.
In short, it needs to be able to look at alternatives.
The problem is that, over the past generation, academic economics had tended to become an ideology which accepted no other theory, no other possibility, and certainly no history - which closed its eyes to the evidence when it was inconvenient.
It was as if economics had divorced itself from the real world.
What if Money Grew on Trees?
Now, it just so happened that Ivy Press was publishing a series of books with the collective title 'What If?'. The first was What If Einstein was Wrong?, a series of 50 short, readable speculations about physics, relativity and quantum theory.
And when the idea that the world could be no other way than the way it is takes over, then asking the question "What if?" can be revolutionary.
So we were delighted to be asked to be involved with the second one in the series, which was eventually called What if Money Grew on Trees?
The book also explores other questions: what if everyone was rich? What if the world stopped flying? What if tulips became as expensive as gold?
The answers are as honest as we could make them, because there are inconvenient truths to every possibility - strange side effects, and weird, unpredictable consequences.
Our aim is to restore to economics the art of possibility - and a sense that economics remains wide open to innovation, fresh insights and new ways to understand the world.
David Boyle and Andrew Simms were among the authors of What if Money Grew on Trees? published by Ivy Press.
David and Andrew are holding a public debate on What If ... in Brighton on the 9th of February. More information via Facebook.