Image copyright Levy Economics Institute of Bard College

American economist Hyman Minsky, who died in 1996, grew up during the Great Depression, an event which shaped his views and set him on a crusade to explain how it happened and how a repeat could be prevented, writes Duncan Weldon.

Minsky spent his life on the margins of economics but his ideas suddenly gained currency with the 2007-08 financial crisis. To many, it seemed to offer one of the most plausible accounts of why it had happened.

His long out-of-print books were suddenly in high demand with copies changing hands for hundreds of dollars - not bad for densely written tomes with titles like Stabilizing an Unstable Economy.

Senior central bankers including current US Federal Reserve chair Janet Yellen and the Bank of England's Mervyn King began quoting his insights. Nobel Prize-winning economist Paul Krugman named a high profile talk about the financial crisis The Night They Re-read Minsky.

Here are five of his ideas.

Stability is destabilising

Minsky's main idea is so simple that it could fit on a T-shirt, with just three words: "Stability is destabilising."

Most macroeconomists work with what they call "equilibrium models" - the idea is that a modern market economy is fundamentally stable. That is not to say nothing ever changes but it grows in a steady way.

To generate an economic crisis or a sudden boom some sort of external shock has to occur - whether that be a rise in oil prices, a war or the invention of the internet.

Minsky disagreed. He thought that the system itself could generate shocks through its own internal dynamics. He believed that during periods of economic stability, banks, firms and other economic agents become complacent.

They assume that the good times will keep on going and begin to take ever greater risks in pursuit of profit. So the seeds of the next crisis are sown in the good time.

Three stages of debt

Minsky had a theory, the "financial instability hypothesis", arguing that lending goes through three distinct stages. He dubbed these the Hedge, the Speculative and the Ponzi stages, after financial fraudster Charles Ponzi.

Ponzi schemes Image copyright AP Similar to a pyramid scheme, an enterprise where - instead of genuine profits - funds from new investors are used to pay high returns to current investors. Named after fraudster Charles Ponzi (1882-1949), such schemes are destined to collapse as soon as new investment tails off or significant numbers of investors simultaneously wish to withdraw funds.

In the first stage, soon after a crisis, banks and borrowers are cautious. Loans are made in modest amounts and the borrower can afford to repay both the initial principal and the interest.

As confidence rises banks begin to make loans in which the borrower can only afford to pay the interest. Usually this loan is against an asset which is rising in value. Finally, when the previous crisis is a distant memory, we reach the final stage - Ponzi finance. At this point banks make loans to firms and households that can afford to pay neither the interest nor the principal. Again this is underpinned by a belief that asset prices will rise.

The easiest way to understand is to think of a typical mortgage. Hedge finance means a normal capital repayment loan, speculative finance is more akin to an interest-only loan and then Ponzi finance is something beyond even this. It is like getting a mortgage, making no payments at all for a few years and then hoping the value of the house has gone up enough that its sale can cover the initial loan and all the missed payments. You can see that the model is a pretty good description of the kind of lending that led to the financial crisis.

Minsky moments

The "Minsky moment", a term coined by later economists, is the moment when the whole house of cards falls down. Ponzi finance is underpinned by rising asset prices and when asset prices eventually start to fall then borrowers and banks realise there is debt in the system that can never be paid off. People rush to sell assets causing an even larger fall in prices.

Image copyright Rex Features Image caption The Minsky moment: Like the moment when the cartoon character realises they're running on thin air

It is like the moment that a cartoon character runs off a cliff. They keep on running for a while, still believing they're on solid ground. But then there's a moment of sudden realisation - the Minsky moment - when they look down and see nothing but thin air. Then they plummet to the ground, and that's the crisis and crash of 2008.

Finance matters

Until fairly recently, most macroeconomists were not very interested in the finer details of the banking and financial system. They saw it as just an intermediary which moved money from savers to borrowers.

This is rather like the way most people are not very interested in the finer details of plumbing when they're having a shower. As long as the pipes are working and the water is flowing there is no need to understand the detailed workings.

Image copyright AP Image caption The 2008 crash brought wider attention to the workings of the financial system

To Minsky, banks were not just pipes but more like a pump - not just simple intermediaries moving money through the system but profit-making institutions, with an incentive to increase lending. This is part of the mechanism that makes economies unstable.

Preferring words to maths and models

Minsky remembered "Hy was a bigger than life kind of person, quite a character," remembers Lawrence Meyer, economist and former Federal Reserve governor, who worked with Minsky at Washington University. "He kind of loved to shock people. He took great joy in that, I think."

"He was more driven by seeing the conventional theories being a delusional thing, a Disneyworld view of the real world," says Australian economist Prof Steve Keen. "He was much more for getting your hands dirty in the real world. I think Minsky gave us the first sensible overview of capitalism ever, which had warts and all what capitalism is about."

Since World War Two, mainstream economics has become increasingly mathematical, based on formal models of how the economy works.

To model things you need to make assumptions, and critics of mainstream economics argue that as the models and maths became more and more complex, the assumptions underpinning them became more and more divorced from reality. The models became an end in themselves.

Although he trained in mathematics, Minsky preferred what economists call a narrative approach - he was about ideas expressed in words. Many of the greats from Adam Smith to John Maynard Keynes to Friedrich Hayek worked like this.

While maths is more precise, words might allow you to express and engage with complex ideas that are tricky to model - things like uncertainty, irrationality, and exuberance. Minsky's fans say this contributed to a view of the economy that was far more "realistic" than that of mainstream economics.

Analysis: Why Minsky Matters is broadcast on BBC Radio 4 at 20:30 GMT, 24 March 2014 or catch up on BBC iPlayer

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