Learning isn’t necessarily cumulative. Human experience over the centuries provides lessons, some clearer than others. But each generation has to learn lessons anew, and some do not.

The lessons about economic growth taught over the long run of history are clear. Growth is not inevitable, and while riches may be accumulated, or appropriated, by the few in high positions, the lives of the very large majority throughout the centuries have been nasty, brutish and short.

The exception, the Great Enrichment, began some three centuries ago, around the North Sea, in the Dutch Republic and England, according to economic historian Deirdre McCloskey, in societies when people began respecting and encouraging commerce, rather than resenting and scorning it.

They discovered that when people exchanged goods and services in free markets, with property rights secured by limited government and the rule of law, economies could grow in ways that improved the lives of not just the few but the many.

Suddenly, and not just for a moment, the great masses of people went from living on $3 a day, just barely subsistence, and in times of famine or war not even that, to $130 a day.

The 20th century proved full of lessons for how to produce extended and widely distributed economic growth — and how to squelch it. Growth occurs when free markets are allowed to operate in societies with high levels of trust and the rule of law.

It ceases, and living standards plummet, in societies where governments flood the economy with currency, try to control wages and prices, impose centralized economic planning, and outlaw voluntary market transactions.

Governments sometimes impose such measures temporarily in wartime, with various results depending on the course of the war. In peacetime, the results are destructive — in Weimar Germany, the Soviet Union, Mao Zedong’s China and, most recently, oil-rich Venezuela.

And, perhaps, in Kamala Harris’ America. Since President Joe Biden ended his candidacy for reelection four weeks ago, the vice president has said remarkably little about what policies she would pursue as president. Her website has had no issues section.

She has taken almost no questions and has undergone nothing like an intensive interview from the press — most members of which, in their enthusiasm for her candidacy, have shown no discomfort at her neglect.

Only last Friday did she begin talking issues, announcing “the first-ever federal ban on price gouging” — she read the word as “gauging” — “on food and groceries.” Presumably, this was an attempt to address an obvious vulnerability for any candidate with a Biden-Harris pedigree, the fact that administration policy, by showering money on consumers already flooded with lockdown-accumulated cash, stoked inflation that no voter under 60 had experienced as an adult.