Piketty’s central theme is the force of interest on inherited wealth causing, he claims, increasing inequality of the income earned from the wealth. In 2014 he declared to the BBC’s Evan Davis that “money tends to reproduce itself,” a complaint about money and its interest rate repeatedly made in the West since Aristotle. As the philosopher said of some men, “the whole idea of their lives is that they ought either to increase their money without limit, or at any rate not to lose it… . The most hated sort [of increasing their money]… is usury, which makes a gain out of money itself.”

Piketty’s theory is that the yield on capital usually exceeds the growth rate of the economy, and so the share of capital’s returns in national income will steadily increase, simply because interest income is growing faster than the income the whole society is getting. Let us therefore bring in the government to implement “a progressive global tax on capital” — to tax the rich. It is, he says, our only hope. Reading the book is a good opportunity to understand the latest of the leftish worries about capitalism, and to test its economic and philosophical strength. Piketty’s worry about the rich getting richer is indeed merely the latest of a long series going back to Thomas Malthus, David Ricardo, and Karl Marx. Since those founding geniuses of classical economics, trade‐​tested progress has enormously enriched large parts of humanity — which is now seven times larger in population than in 1800 — and bids fair in the next 50 years or so to enrich everyone on the planet. And yet the left routinely forgets this most important secular event since the invention of agriculture — the Great Enrichment of the last two centuries — and goes on worrying and worrying in a new version every half generation or so.

All the worries, from Malthus to Piketty, share an underlying pessimism, whether from imperfection in the capital market or from the behavioral inadequacies of the individual consumer or from the Laws of Motion of a Capitalist System. During such a pretty good history from 1800 to the present, the economic pessimists on the left have nonetheless been subject to nightmares of terrible, terrible faults. Admittedly, such pessimism sells. For reasons I have never understood, people like to hear that the world is going to hell, and become huffy and scornful when some idiotic optimist intrudes on their pleasure. Yet pessimism has consistently been a poor guide to the modern economic world.

SUPPLY, DEMAND, AND CREATIVE DESTRUCTION

The technical flaws in Piketty’s argument are pervasive. When you dig, you find them. The fundamental problem is that Piketty does not understand how markets work. In keeping with his position as a man of the left, he has a vague and confused idea about how supply responds to higher prices. Startling evidence of Piketty’s miseducation occurs as early as page 6.

He begins by seeming to concede to his neoclassical opponents: “To be sure, there exists in principle a quite simple economic mechanism that should restore equilibrium to the process: the mechanism of supply and demand. If the supply of any good is insufficient, and its price is too high, then demand for that good should decrease, which would lead to a decline in its price.” The words I italicize clearly mix up movement along a demand curve with movement of the entire curve, an error of first‐​term college students. The correct analysis is that if the price is “too high” it is not the whole demand curve that “restores equilibrium,” but an eventually outward‐​moving supply curve. The supply curve moves out because entry is induced by the smell of super‐​normal profits.

Piketty does not acknowledge that each wave of inventors, entrepreneurs, and even routine capitalists find their rewards taken from them by entry. Look at the history of fortunes in department stores. The income from department stores in the late 19th century, in Le Bon Marché, Marshall Field, and Selfridge’s, was entrepreneurial. The model was then copied all over the rich world. In the late 20th century the model was challenged by a wave of discounters, and they then in turn by the internet. What happens is that the profit going to the profiteers is more or less quickly undermined by outward‐​shifting supply. The original accumulation dissipates. The economist William Nordhaus has calculated that the inventors and entrepreneurs nowadays earn in profit only 2 percent of the social value of their inventions. If you are Sam Walton the 2 percent gives you personally a great deal of money from introducing bar codes into stocking of supermarket shelves. But 98 percent at the cost of 2 percent is nonetheless a pretty good deal for the rest of us. The gain from macadamized roads or vulcanized rubber, then modern universities, structural concrete, and the airplane, has enriched even the poorest among us.

HUMAN CAPITAL AND INEQUALITY

This brings me to the next technical problem. Piketty’s definition of wealth does not include human capital, owned by the workers, which has grown in rich countries to be the main source of income, when it is combined with the immense accumulation since 1800 of capital in knowledge and social habits, owned by everyone with access to them. Once upon a time, Piketty’s world without human capital was approximately our world, that of Ricardo and Marx, with workers owning only their hands and backs, and the bosses and landlords owning all the other means of production. But since 1848 the world has been transformed by what sits between the workers’ ears.

The only reason in the book to exclude human capital from capital appears to be to force the conclusion Piketty wants to achieve. One of the headings in Chapter 7 declares that “capital [is] always more unequally distributed than labor.” No it isn’t. If human capital is included — the ordinary factory worker’s literacy, the nurse’s educated skill, the professional manager’s command of complex systems, the economist’s understanding of supply responses — the workers themselves, in the correct accounting, own most of the nation’s capital — and Piketty’s drama falls to the ground.

Finally, as he candidly admits, Piketty’s own research suggests that only in the United States, the United Kingdom, and Canada has income inequality increased much, and only recently. In other words, his fears were not confirmed anywhere from 1910 to 1980; nor anywhere in the long run at any time before 1800; nor anywhere in Continental Europe and Japan since World War II; and only recently, a little, in the United States, the United Kingdom, and Canada. That is a very great puzzle if money tends to reproduce itself as a general law. The truth is that inequality goes up and down in great waves, for which we have evidence from many centuries ago down to the present, which also doesn’t figure in such a tale.

Sometimes Piketty describes his machinery as a “potentially explosive process.” At other times, he admits that random shocks to a family fortune means that “it is unlikely that inequality of wealth will grow indefinitely … rather, the wealth distribution will converge toward a certain equilibrium.” On the basis of the Forbes lists of the very rich, Piketty notes, for example, “several hundred new fortunes appear in [the $1 billion to $10 billion] range somewhere in the world almost every year.” Which is it, Professor Piketty? Apocalypse or a steady share of rich people constantly dropping out of riches or coming into them, in evolutionary fashion?

The science writer Matt Ridley has offered a persuasive reason for the slight rise in inequality recently in Britain. “Knock me down with a feather,” Ridley writes: