Weyer, Johann

Weyer, Johann (1515–1588) was a Dutch physician who argued against the witch hysteria and the alleged workings of the Devil through people and Pacts. Johann Weyer accepted the existence of Demons and their ability to wreak evil and cause Possession, but he opposed the torture and execution of accused witches during the Inquisition and refuted the belief that the Devil recruited people to cause harm.


Weyer was born the middle of three sons to a Protestant family in Brabant. His father was a hops merchant who could afford to give his sons a good education. Weyer was 15 when he went to study in the household of Heinrich Cornelius Agrippa von Nettesheim, a prominent physician, philosopher, and occult scholar. Agrippa taught Weyer Platonic and Neoplatonic philosophy and introduced him to the occult works of Abbot Johannes Trithemius of Sponheim.

The seeds of Weyer’s skepticism about the witch hysteria that gripped the 16th century may have been planted by Agrippa, who once defended an old woman accused of witchcraft, arguing that she was feeble-minded, not diabolical.

Weyer’s apprenticeship with Agrippa lasted for about four years. Weyer studied medicine at the University of Paris in 1534, and at the University of Orléans from 1534 to 1537. He learned the prevailing medical doctrine, still in force from ancient times, that health depends on the balance of four humors in the body: Blood, phlegm, bile, and black bile, or melancholy.

After graduation, Weyer returned to Brabant and nearby Ravenstein to work as a physician. In 1545, he became the municipal physician for Arnhem, a much bigger city. At about the same time, he married Judith Wintgens, with whom he had four sons and a daughter.

In 1550, Weyer was appointed to a prestigious post that he held for most of the rest of his career, as personal physician to Duke William V of Julich-Berg-Cleves in Dusseldorf. Though Catholic, the duke was liberal-minded, and Weyer enjoyed a comfortable relationship with him. He pursued scholarly studies and writing.

In 1578, he retired from his post with the duke. He was succeeded by one of his sons, Galenus, named after the famous Roman physician Galen. Weyer continued to write and practice medicine until his death in Tecklenburg on February 24, 1588.


Weyer wrote on medicine and philosophy; of importance to the subject of Demonology is his main work, De praestigiis daemonum, et incantationibus, ac veneficiis (On the illusions, spells and poisons of Demons), published in 1563, in which he attacked many of the prevailing beliefs of inquisitors. Weyer revised and added to the work several times up to 1583.

In 1577, he added an appendix, Pseudo-Monarchia (The false kingdom of the Demons), to De praestigiis daemonum. It is an inventory and description of 68 principal Demons, their characteristics, and how they may be conjured. The princes rule 7,405,926 Demons organized in 1,111 Legions of 6,666 each. Later, the Lutheran Church thought Weyer’s estimate too low and raised the census of the Demonic population to 2,665,866,746,664, or roughly 2.6 trillion.

Reginald Scot, a contemporary who agreed with Weyer, translated Pseudo-Monarchia and included it in his book The Discoverie of Witchcraft (1584). The magical grimoire the Lemegeton, also called The Lesser Key of Solomon, lists the same 68 spirits and adds four more, and it gives Seals for their conjuration. The 72 are also known as Spirits of Solomon.

Weyer wrote De lamiis liber (On Witchcraft) in 1577. He used the term Lamiae to describe female witches who thought they had pacts with the Devil.

Views on Demons and Witches

Weyer rejected the Aristotelian view that Demons did not exist in reality. He believed in the Devil and his legions of Demons but did not believe that witches were empowered by the Devil to harm humankind. Nor did he believe stories of their flying through the air and attendance at Sabbats in which the Devil was worshipped and babies were eaten. He thought that belief in Witchcraft was caused by the Devil and that the church ironically served the cause of the Devil by promoting belief in the evil power of witches.

In De praestigiis daemonum, Weyer refuted the idea of the Demonic pact because there was no basis for it in the Bible. He gave a rational analysis of reports of alleged witch activity and concluded that most witches were deluded and mentally disturbed old women, the outcasts of society, who were fools, not heretics. Some might wish harm on their neighbours but could not carry it out. If harm occurred coincidentally, they believed, in their delusion, that they had brought it about. He did believe that some witches served Satan and did harm people, but not through supernatural means. He urged the church to forgive those who repented or, at most, to levy fines upon them.

Weyer believed that Demons could possess people; however, he advocated ruling out all medical and natural explanations and causes before looking for the supernatural.

Weyer successfully discouraged witch-hunting in much of the Netherlands for a while but was forced out by the Catholic governor, the duke of Alba. His book had almost the opposite effect from the one he intended. He was savagely denounced by critics such as Jean Bodin and King James VI AND I, both of whom favoured the extermination of witches. James’ authoring of his anti witch treatise, Daemonologie, was in response to the works by Weyer and Scot.

Bodin urged that copies of Weyer’s book be burned. Others wrote books refuting Weyer, and these helped to stimulate more witch hunts. Weyer himself was accused of being a witch but was not formally charged. However, his arguments did persuade many witch hunters in Germany to consult physicians more often to rule out medical causes.


  • Ankarloo, Bengt, and Gustav Henningsen, eds. Early Modern European Witchcraft: Centres and Peripheries. Oxford: Clarendon Press, 1990.
  • Russell, Jeffrey B. A History of Witchcraft. London: Thames & Hudson, 1980.
  • Weyer, Johann. On Witchcraft (De praestigiis daemonum). Abridged. Edited by Benjamin G. Kohl and H. C. Erik Midelfort. Asheville, N.C.: Pegasus Press, 1998.


The Encyclopedia of Demons and Demonology – Written by Rosemary Ellen Guiley – Copyright © 2009 by Visionary Living, Inc.

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