The Economist’s list of big economic ideas moved forward, presenting John Maynard Keynes’ idea of the fiscal multiplier. The most important contribution of Keynes’ magnum opus — The General Theory of Employment, Interest, and Money — “is the reasoning behind the proposition that when an economy is operating below full employment, demand rather than supply determines the level of investment and national income.”

The idea of Keynes’ multiplier effect, which reemerged after the 2008 financial crash, supported the notion that extra money spent by governments would add directly to national output and income, first by reaching direct contractors, suppliers, and civil servants who, in turn, would spend the extra income on other goods and services and so on. “Should the government cut back, the ill effects would multiply in the same way.”

Keynes’ ideas received plenty of criticism in the 1970s, peaking in 1979 with an article published by eventual Nobel laureates Robert Lucas and Tom Sargent titled “After Keynesian Economics,” suggesting that the flaws in Keynesian economic models were “fatal.”

But he’s back in style again: Now, after the great recession, plenty of economists “argue that insufficient fiscal stimulus has been among the biggest failures of the post-crisis era… austerity has substantially reduced growth, leading to levels of public debt that are higher than they would have been had enthusiastic stimulus been used to revive growth.” Next up in The Economist’s series is a brief on The Nash Equilibrium, the basic tenet of game theory.