Extraordinary Popular Delusions and The Madness of Crowds summary

In 1660, an Italian alchemist named Giuseppe Francesco Borri convinced Sweden's Queen Christina that he could create a universal medicine that would cure all diseases. By 1670, he had talked his way into the court of Denmark's Frederick III with promises of turning metal into gold. When Frederick III died, Borri fled to Vienna, then to Amsterdam, leaving a trail of wealthy patrons with empty pockets and unfulfilled promises. Like many successful alchemists, he combined scientific knowledge with showmanship, making his claims sound just plausible enough to keep the money flowing.

Mackay found dozens of similar cases across Europe spanning three centuries. Court records showed that Holy Roman Emperor Rudolf II spent a fortune supporting over 200 alchemists at his castle in Prague. King Philip II of Spain handed over massive sums to alchemists despite his country's mounting debts. Fascinatingly, the same tricks worked repeatedly in different countries and contexts.

In 1730, a group of Capuchin monks in Orleans, France, began reporting terrifying disturbances in their monastery. They claimed the ghost of their recently deceased prior was haunting the halls. The spirit would knock on doors at midnight, drag chains through corridors, and enter the chapel at strange hours. When church authorities investigated, the monks produced letters allegedly written by the ghost itself, demanding they be moved to a grander monastery. 

The haunting became so severe that the monks insisted they couldn't possibly continue living there. Their superiors eventually granted them a newer, larger monastery in a more desirable part of the city. Soon after they moved, the hauntings mysteriously stopped. Mackay discovered through local records that the monks had been complaining about their old building's poor condition for years before devising their ghostly solution.

Between 1563 and 1736, Scotland executed nearly 4,000 people for witchcraft. In one notorious case from 1590, the town of North Berwick accused dozens of local women and men of using magic to create storms to sink King James VI's ships. Under torture, the accused confessed to impossible acts, including meetings with the devil. The king personally oversaw many trials, and wrote a book promoting witch hunting that spread these ideas across Europe.

Mackay documented how witch hunts typically began with a community facing problems like failed crops, sick livestock, or dying children. People desperately wanted someone to blame. Usually, suspicion fell on social outcasts — elderly women living alone, healers using traditional remedies, or anyone who seemed different. One accusation would spiral into many as torture produced false confessions implicating others.

In 1789, Londoners became obsessed with a meaningless word: Quoz. The slang term spread through every social class, from street vendors to aristocrats. People would shout it as an insult, use it as an answer to serious questions, or drop it into conversation to seem fashionable. 

Nobody knew what it meant, but for several months, not knowing how to use Quoz marked you as completely out of touch. Mackay documented that, oddly,  the word vanished as quickly as it appeared, leaving no trace of its original meaning.