The extraordinary ways the brain can misfire: Why would someone wake up and claim they’re Napoleon? Or why would they believe they have been turned into a wolf and demand to be fed raw meat?

For centuries, people have dismissed delusions as a problem for the shrinks to sort out in distant asylums. But delusions are more than just bizarre case studies. They tell stories of collective anxieties and traumas.

Examining the study and documentation of delusions over time, Shepherd looks at 10 extraordinary cases of delusion from the archives. Included here are the paranoid conspiracy of James Tilly Matthews, an 18th-century spy in revolutionary France, and Madame X, who in 1923 demanded a divorce on the grounds that her husband had been substituted for a double. Also here are King Charles VI of France, who believed that he was made of glass, and Léa-Anna B, who was convinced that King George V was in love with her. A History of Delusions covers what psychological purpose these alternative realities might serve, given how common delusions are in the general population, and what wider societal stresses they might portend.

In this groundbreaking history, Victoria Shepherd explores delusions from ancient times to present and implores us to identify reason in apparent madness. Isn’t it perfectly understandable to believe you’ve got the wrong head when the guillotine takes the heads of hundreds every day? Who cannot sympathize with the man who believes he is already dead, when all his comrades died in the battlefields?

We all have it in us to become delusional. In understanding delusions, we come closer to understanding ourselves.