In January 1632, a student named Johann Geisler walked into an examination hall at the University of Ingolstadt to defend fifty theses on nature, art, and magic. His professor and examiner was Conrad Henzel, a Jesuit, Ordinary Professor of Philosophy and Dean of the Faculty. The thesis was printed by Gregorius Haenlin’s press, bound in quarto, and dedicated to one of the most powerful men in the Holy Roman Empire.
That man was Werner Tserlaes, Count of Tilly, commander of the Catholic League armies and military governor of Ingolstadt. The dedicatory letter describes a world at war. “Everything is thrown into disorder by the tumults of war,” Geisler wrote. “The smoke of a fire spreading from nearby already threatens the borders of our Bavaria.” He described knocking on the doors of noblemen and finding no one home. Some were paralyzed with fear. Others were laboring in war councils. “Nowhere does Pallas appear except in armor.”
Tilly, he said, was the exception: a general who still read books between battles, whose daily habit was the walk from his armory to his library. Geisler asked only for the last corner of the lowest shelf.
Tilly would be mortally wounded at the Battle of Rain am Lech on April 15, 1632, less than four months after the thesis was printed. Swedish cannonfire shattered his leg. He died on April 30 at Ingolstadt, the city where Geisler had defended his theses.
The Disputatio
A disputatio was the standard examination format at Jesuit universities. The professor set the theses. The student defended them publicly against objections from faculty and audience. The printed text served as both study guide and academic record.
Geisler’s disputation covered three subjects in fifty theses. Chapter One defined nature in the Aristotelian sense: the internal principle of motion and rest. Chapter Two examined art, meaning craft and technique, including a discussion of whether alchemy could produce real gold. Chapter Three, the longest and strangest, cataloged magic: what it was, how it worked, and what demons could and could not do.
The primary authorities cited were Aristotle, Thomas Aquinas, the Coimbra commentators (a series of Jesuit textbooks from the University of Coimbra in Portugal), Francisco Suarez, Benito Pereira, and Martin Del Rio. Del Rio’s Disquisitiones Magicae, published in 1599-1600, provided the demonological framework. It was the standard Jesuit reference work on the subject and, in the decades after its publication, served as a manual for judges and inquisitors conducting witch trials across Catholic Europe.
The University of Ingolstadt was Bavaria’s premier institution and a Jesuit stronghold. The Society of Jesus had controlled its theology and philosophy faculties since the 1550s. A century and a half later, in 1776, a professor of canon law at the same university named Adam Weishaupt would found the Order of the Illuminati. In 1632, that irony lay far in the future. The university’s business was defending Catholic orthodoxy against Protestantism, and part of that business was teaching students exactly where the line between legitimate knowledge and demonic deception fell.
Can You Make Gold?
Chapter Two of the disputation takes up art, craft, and technique. The Jesuits defined art (in the Aristotelian sense) as “a habit of making with true reason,” meaning a stable skill that operates by passing into external matter according to fixed rules. A sculptor works stone. A physician compounds medicines. The art directs; nature does the actual producing.
The interesting question comes in Thesis XXVII: can alchemy produce real gold?
Geisler and Henzel take a position that might surprise anyone expecting blanket condemnation. They say yes, in principle. Gold transmutation is theoretically possible. The causes that produce gold in the bowels of the earth could, in theory, be assembled above the earth by human effort. They cite Arnold of Villanova, the 13th-century physician and alchemist, who reportedly produced real gold in Rome.
The catch: it is “extremely difficult and consequently exceedingly rare.” The evidence is overwhelmingly against success. Most alchemists fail. Many are frauds.
They tell the story of Marcus Bragadino, a Venetian who arrived in Munich claiming he could manufacture gold. Bavarian nobles invested heavily. Bragadino delivered what looked like fresh gold. In 1591, the truth came out: he had been melting genuine gold dust, mixed into charcoal, and presenting the result as transmuted metal. He confessed publicly and was executed in Munich.
The Jesuit position was precise. Alchemy as a theoretical discipline was legitimate. The transmutation of metals was within the bounds of natural philosophy. But the practice was so difficult that virtually every claimed success was a fraud. The framework left the door open while slamming it on almost everyone who tried to walk through.
The same careful line-drawing would define their approach to the next subject.
Two Kinds of Magic
Chapter Three begins with a definition. Magic, following Del Rio, is “an art or faculty which, by created and not supernatural power, produces certain marvels and unusual things whose cause surpasses the sense and ordinary understanding of men.”
The Jesuits divided magic into two categories and rejected the existence of a third.
Natural magic was legitimate. It meant a deeper knowledge of nature’s secrets: observing the courses of the stars, the sympathies and antipathies of substances, and applying the right things to the right things at the right time and place. The results looked miraculous to the ignorant. They followed from natural causes that the practitioner understood better than most. Thomas Aquinas taught that God gave this knowledge to Adam at creation, and that Adam passed it to his descendants. The Jesuits accepted this. Natural magic was the noblest part of physics and medicine.
It was also dangerous. Lessius, one of their cited authorities, warned that natural magic “violently captivates the already curious human mind toward useless and curious things and gradually lures it toward superstitious magic.” The slippery slope was built into the discipline.
Superstitious, black, or demonic magic (what the Greeks called goeteia) operated through a pact with a demon, either explicit or tacit. Where natural magic used natural causes, demonic magic used signs: words, gestures, symbols, figures. These signs had no natural power. They worked because they activated the terms of a deal. The demon did the actual work.
The Platonists had claimed a third category: theurgia, white magic communicated by God or good angels. The Jesuits rejected this completely. Del Rio called it “fictitious and in no way different from black magic, merely concealed under a more honorable name for the ruin of the incautious.” God does not involve Himself or His angels in magical operations. Beyond natural magic and demonic magic, no third kind exists.
Two categories. No exceptions. If it worked and natural causes could not explain it, a demon was involved.
What Demons Can Do
The disputation’s catalog of demonic abilities reads like a technical manual. The Jesuits approached the subject the way an engineer might approach a list of machine specifications. Demons have two kinds of external action: immediate (direct physical force) and mediate (applying natural agents to patients with superhuman skill).
The key principle: demons are master craftsmen of nature. They know the properties of every substance, every force, every combination, and apply this knowledge with a speed and precision humans cannot match. Their power comes from working within the laws of nature, not from breaking them.
Here is what the 1632 thesis says they can do:
Fire and storms. Demons can gather fire “from the concavity of the Moon or elsewhere” and send it to devastate cities and kingdoms. They can raise winds that topple houses (the text cites Job 1) and cause terrible storms on land and sea.
Transport. They can move large bodies from one place to another almost instantaneously. This includes carrying witches through the air, which the thesis treats as physically real. Christ himself was carried to the pinnacle of the Temple and to a high mountain by the Devil, as described in Matthew 4.
Animation. They can make statues or other lifeless things appear to walk on their own. They can form articulate speech in or near objects, making animals or statues seem to speak in human voices.
Illusion and substitution. They can show the forms and appearances of exotic goods and treasures, or physically produce actual objects brought from elsewhere. The Egyptian magicians’ staffs turning into serpents (Exodus 7:12) were likely a substitution: the demon removed the real staffs and put snakes in their place.
Rivers and water. They can divide river water and drive it backward against its nature, back to its source.
Assumed bodies. They can take on various physical forms, wearing the remains of dead creatures or shaping bodies from air or other matter. The bodies are convincing to sight but, the Jesuits argued, can probably always be detected by touch. Christ proved he was real and not a demonic phantom by saying: “Touch me and see, for a spirit does not have flesh and bone, as you see that I have” (Luke 24:39).
Every ability on this list follows from two basic powers: local motion (moving things from place to place) and superior knowledge of natural causes (knowing which combinations produce which effects). Demons produce no miracles. They produce natural effects at unnatural speed.
What Demons Cannot Do
The limits are as specific as the abilities. The thesis draws each boundary from the same Aristotelian-Thomistic framework, and each limit tells us something about how the Jesuits understood the architecture of reality.
They cannot create perfect animals. Following Thomas Aquinas and Augustine, the “more common opinion of the theologians” held that demons cannot generate complete living creatures from scratch. They can only steal seeds from elsewhere and introduce them into a womb by some means.
They cannot overturn the universe. They cannot move entire principal parts of the world from their places, stop the heavens, create a vacuum, or make bodies pass through each other. The large-scale structure of creation is beyond their reach.
They cannot produce forms directly. Demons cannot, from themselves, immediately produce any substantial or accidental form in bodies (except for location and probably impulse). They rearrange. They do not create.
They cannot truly transform one thing into another. A human turned into a cat, a dog, or a wolf is always an illusion. The demon can make it look like a transformation happened. The underlying substance remains unchanged. This position had direct implications for werewolf trials: the Jesuit framework said physical transformation was impossible, which meant any reported werewolf was either a demonic illusion or a deluded person.
They cannot raise the dead. Resurrection is reserved to God alone.
They cannot predict free-will choices. Future contingent events that depend on the free will of a human being are unknowable to demons “certainly and infallibly.” They can, however, make extremely sharp guesses. The text says demons conjecture about human thoughts “most acutely” from changes in facial expression, the flickering of eyes, and acts of the imagination. They read body language better than any human can. They know what you are likely to choose. They do not know what you will choose.
They cannot read minds. The free inclinations of the will and the operations of the intellect are hidden from them. The interior of the human mind is God’s territory.
The pattern is consistent. Demons have enormous power over the physical world and zero power over the spiritual one. They can move anything made of matter, yet they cannot touch anything made of will.
The Diagnostic Rule
The disputation’s final thesis is the most consequential. Thesis L states:
Where neither the force of miracle, nor of nature, nor of artful skill is found, a pact with the Devil is present.
This sentence was a practical tool. Del Rio supplied three diagnostic tests, organized by what you could examine:
From the cause. If the cause is obviously inadequate to produce the observed effect, according to the judgment of prudent men. If the demon himself is invoked. If the prayers used contain foreign, meaningless, incoherent, or false words. If signs, figures, or bindings are used contrary to ordinary Church practice. Any of these marks the presence of superstition.
From the quality of the action. If the operations involve conditions that remove them from the ordinary course of nature. The examples are vivid: if many miles are traversed in the shortest time. If a sick person, a horse, or a falling mountain is stopped instantly by mere touch. If you pierce an image of Socrates here and he drops dead at the same moment in Rome. If you bind a staff or dagger here and a wound inflicted by it is healed in Munich.
From the effect itself. If the effects exceed all natural skill and power in their substance (such as restoring life or whole limbs), and no evident holiness of the person or outstanding goodness of purpose claims them as heavenly, then “hold for certain that behind them lurk the deceptions of evil demons.”
This framework was the intellectual machinery behind the witch trials of the 16th and 17th centuries. A judge examining a suspected witch could apply these three tests. If a woman healed a sick child by touching it and no natural cause could explain the cure, and she showed no signs of special holiness, the framework pointed to one conclusion: demonic pact. The exorcism traditions across cultures also relied on identifying supernatural agency, but the Jesuit diagnostic went further. It provided a checklist.
Del Rio’s Disquisitiones Magicae was cited in courtrooms. The six volumes contained case studies, legal procedures, interrogation methods, and theological justifications. The 1632 Ingolstadt disputatio taught the next generation of Jesuit-educated lawyers, priests, and administrators the same framework in condensed form. A student who passed this exam walked out knowing exactly how to identify the Devil’s work, according to the best authorities of his Church.
What the Exam Reveals
The two Jesuit censors who reviewed the thesis before publication approved it warmly. Georgius Liprandus, Professor of Sacred Theology, called the material “most useful for many” and “most worthy of printing and public examination.” Petrus Hildebrandt, Professor of Sacred Languages and Mathematics, praised it for teaching “clearly and learnedly wherein the difference between the true and false arts of the demon consists.”
The text closes with four words: Omnia ad maiorem Dei gloriam. All to the greater glory of God. The Jesuit motto.
What the exam reveals, four centuries later, is a mind trying to be systematic about the unseen. The Jesuits were trained Aristotelian philosophers building a rational framework for the irrational. Every demonic ability had a mechanical explanation, every limit a theological reason. The system was internally consistent, logically rigorous, and, from the outside, terrifying in its completeness.
The Grand Grimoire, written roughly a century and a half later, organized Hell as a French bureaucracy with office hours and contracts. The Ars Goetia listed seventy-two demons with individual specialties and ranks. The Testament of Solomon, written perhaps fifteen centuries earlier, had a king interrogating demons one by one to learn their names and weaknesses. All these texts shared an assumption: that the demonic world could be cataloged, classified, and understood through careful observation and proper method.
The 1632 Ingolstadt disputatio is the academic version of the same impulse. Where the grimoires offered recipes, the Jesuits offered a taxonomy. Where the historical Faust or Paracelsus blurred the line between natural philosophy and forbidden knowledge, the Jesuits drew it with a ruler and fifty theses.
Whether the line was drawn in the right place is another question. The diagnostic rule in Thesis L sent people to prison and to death. The framework that said demons cannot read minds also said that unexplained healing by an unholy person proved a demonic pact. The same logic that limited demonic power also expanded the definition of demonic involvement to include anything the examiner could not explain.
The thesis ends and the student passes, but the war goes on. Four months later, the patron is dead. The university survives, and the framework survives longer. The questions it tried to answer, about where nature ends and something else begins, survive longest of all.
Read the complete translation of the Disputatio de Natura, Arte, Magia (1632)
