Johann Weyer (1515-1588) was a scholar of medicine, psychiatry - and magic. He wrote what Freud called one of the ten most significant books of all time and calculated the number of demons in the universe. Johann Weyer was truly a man of the Renaissance, working with its doubts and dilemmas throughout his life.

Also known under the names of Weier, Wier, Wierus and Piscinarius, Johann (or Jean) was born in Grave in the Low Countries (Netherlands). He trained as a medical doctor while also studying occultism under Agrippa von Nettesheim. Although he later rejected her neo-Platonistic ideas and alchemy, he retained his belief in magic.

Weyer went to Paris in 1533 to study at the university there, but he completed his education in Orléans in 1537. He worked as a town physician, first at Ravenstein, then Arnhem, before he became personally appointed to Duke William V of Cleve, Julich and Berg.

In 1563 he wrote the book Freud considered so important, De praestigiis daemonum. This book refuted, point by point, the Malleus Maleficarum that the Inquisition loved so. Weyer did not believe in witches, or in witch hunting. The persecuted women and men had not made a pact with the Devil, he said, they were merely possessed by demons - what we would call mentally insane. His work inspired scepticists to debate and abolish the persecution of "witches" in later centuries.

He did believe in the Devil, however, this expert at fooling our senses. Weyer spent a lot of effort studying the devil and his minions, cathegorising the demons under 72 princes and ending at the total number of 7,405,926. But he believed in exorcism and healing, not burning. As methods for curing anger, this most horrible disease of the soul, he suggested exercise, bathing and calming music.

Johann Weyer remained physician for the Duke until he retired to let his son Galenus take over the post. He died 73 years old while working for the duke of Tecklenburg.

(37) Procell is a great and a strong duke, appearing in the shape of an angell, but speaketh verie darklie of things hidden, he teacheth geometrie and all the liberall arts, he maketh great noises, and causeth the waters to rore, where are none, he warmeth waters, and distempereth bathes at certeine times, as the exorcist appointeth him, he was of the order of potestats, and hath fourtie eight legions under his power.

(from Pseudomonarchia daemonum, translated by Reginald Scot in 1584. Source:

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