The ideas of economists—whether they are right or wrong—are often more powerful than commonly understood. Consider President Trump’s statements about the magical powers of tariffs or Mexico’s Sheinbaum’s discourse on import substitution industrialization. Our leaders—even when they believe themselves to be smart and independent thinkers—are often slaves to the ideas of past economists.

This notion is inspired by John Maynard Keynes’s reflection in the concluding notes of his General Theory. For decades, Keynes has been the “slave master” to most world leaders. His ideas, both correct and mistaken, have shaped how people understand the economy—even when those ideas stemmed from Keynes’s own misunderstandings.

There is plenty of literature in economics, courses on macroeconomics, and the history of economic thought that are too quick to throw away the conclusions around the ideas of the Classic School of economics.

Say’s Law is one of the main victims of these express interpretations of the ideas of the classics. For decades, students have been taught that classical economists believed “supply creates its own demand.” Moreover, they are often told that, according to J.B. Say, the market always operates in perfect competition or as it would in an evenly rotating economy. This so-called law is often cited as a pillar of outdated economic thinking—a claim John Maynard Keynes famously used to argue against free-market principles in his General Theory.

What Say actually said in his Treatise on Political Economy was that production creates the means for consumption, which implies that the only way you can acquire the resources to buy goods is by selling valuable goods to others. In other words, that exchange is a two-way street: You produce and/or sell goods valued by others to get money to buy goods.