De Praestigiis Daemonum

Johann Weyer was physician to the Duke of Cleves, and his book of 1563 is the first sustained attempt to argue the accused out of the dock using medicine rather than theology. Its structure matters. Weyer does not begin by denying demons. He grants a great deal about them, and then turns the concession into a weapon.

If the Devil is powerful and deceitful, he argues, then the obvious reading of an old woman confessing to flying to a gathering and blighting a field is not that she did it. It is that she is deceived, or melancholic, or ill, or exhausted, or persuaded by the questioning itself. She lacks the capacity to have done what she says she has done. A court that executes her is punishing a delusion, and the delusion is the Devil's work rather than hers. Weyer describes cases from his own practice, and the descriptions read as clinical observation rather than as demonology.

He was not evenhanded, and the asymmetry is part of the argument. Weyer was severe about the learned male magicians who worked with grimoires and conjurations, on the ground that they acted knowingly and sought demonic help deliberately. His sympathy went to the poor and mostly elderly women who had sought nothing and understood less. Whatever else this is, it is the first widely read book to look at a witch trial and see a patient rather than a defendant.

The book was answered fast and hard. Jean Bodin, a jurist of real standing, published against it in 1580 and argued that a man who defended witches so warmly had something to hide, that Weyer's medical explanations were a screen, and that leniency of this kind was itself a danger to the commonwealth. That exchange is worth knowing about because it shows the cost of dissent: to argue against the trials in the sixteenth century was to invite the suggestion that you were part of what you defended. Weyer had a patron and a court position, and that protection is part of why he could publish at all. The book was placed on the Index of Prohibited Books.

It is equally important to be clear about what Weyer did not claim, because later readers have repeatedly enlarged him. He did not say there is no Devil. He did not say magic is nothing. He did not say the whole category was empty, which is what Reginald Scot would say twenty one years later in English. His case was narrower and, for a working court, more usable: these particular defendants cannot have done these particular things.

Nineteenth century psychiatry adopted him as a founder, and editions were published presenting the book as an early textbook of mental illness. Historians of medicine are cautious about that. The diagnostic vocabulary of 1563 is not the vocabulary of 1860, and reading it as such flatters the book by removing it from the argument it was actually having.