Most economists believe John Maynard Keynes (rhymes with "brains" not "beans") was the greatest economist of the 20th century. But his most famous quote is one I've never been sure I agree with.
He claimed that "the ideas of economists and political philosophers, both when they are right and when they are wrong, are more powerful than is commonly understood.
"Indeed, the world is ruled by little else. Practical men, who believe themselves to be quite exempt from any intellectual influence, are usually the slaves of some defunct economist.
"Madmen in authority, who hear voices in the air, are distilling their frenzy from some academic scribbler of a few years back."
One man who definitely agrees is Barry Schwartz, a professor of psychology at Swarthmore College in Pennsylvania. He writes in his book Why We Work that, where once our ideas about human nature may have come from our parents, our community leaders and our religious texts, these days they come mostly from social science.
"In addition to creating things, science creates concepts, ways of understanding the world and our place in it, that have an enormous effect on how we think and act," Schwartz says.
"If we understand birth defects as acts of God, we pray. If we understand them as acts of chance, we grit our teeth and roll the dice. If we understand them as the product of prenatal neglect, we take better care of pregnant women."
Schwartz says that because ideas aren't objects, to be seen, purchased and touched, they can suffuse through the culture and have profound effects on people before they are even noticed.
And ideas, unlike things, can have profound effects on people even if those ideas are false.
I don't doubt that, in this, both Schwartz and Keynes are right. The social world is far too complex for any of us to really understand how it works. So we observe what's happening and then come up with theories - "models" - about how it works.
Those theories inevitably influence the way we think about the world, the way we react to it and the way we try to get some control over it.
But the world is so complex that we can have lots of different theories about it, or different aspects of it. Many of those theories will have an element of truth and an element of error.
We probably should have a toolbox full of theories, choosing to use the one that best fits the particular issue we're focusing on.
But human nature - our limited cognitive processing power - leads us to simplify things, settling on the one that seems to work best and apply to most circumstances. We remember it, and forget the others.
Often, of course, we don't do a lot of thinking about which theory is best, we just go along with the one most of the people around us seem to believe.
It's also true that the theories and models we rely on, consciously or unconsciously, become, as the sociologists say, "performative" - if enough people believe the world works in certain way and act on that belief, to some extent the world does start to work that way.
There are limits to this, of course. For a few decades economists allowed their dominant model - their group's way of thinking - to convince them the deregulation of the banks had brought us to the era of Great Moderation, of low inflation and unemployment with ever rising prosperity.
Their model blinded them to the global financial crisis that was coming and the years of economic malfunction that would follow.
There could be no more costly demonstration of the inadequacy of their theory about how the world worked.
So no argument: ideas have a huge effect on the world - for good or ill. But does that mean "the world is ruled by little else"?
I doubt it. The main rival for that title is the thing economists exalt above all else: self-interest. What happened to the rich and powerful, don't they have any influence on how the world is ruled?
The more I observe our politics, the more I see it as an unending battle between powerful interest groups. The political parties, contending for their own share of power, negotiate their way around the most powerful of the various interest groups.
The problem is the power democracy still gives to ordinary punters. Should I try to win votes by promising a royal commission, or should I keep in with the banks - and their generous donations to election funds - by promising to bash them with a feather?
So, do ideas really trump vested interests? Surely we're ruled by some combination of the two.
But the more I understand the weaknesses in the economists' dominant ideas about how the economy works and should work, the more I see what a bad predictor their model is, the more I wonder how such a flawed theory remains so dominant, largely impervious even to stuff-ups as monumental as the Great Recession.
Then a terrible thought strikes: maybe their ideas remain so influential in politics and the community because they happen to suit the interests of the rich and powerful.