In the 17th century, Johannes Kepler was not only unlocking the laws of planetary motion but also defending his mother from accusations of witchcraft. This story recounts Kepler's personal battle against superstition and ignorance, using his scientific reasoning and public standing to navigate a legal and social labyrinth. It's a tale of filial devotion, the clash between the nascent scientific world and the old world of fear, and the courage required to stand for reason.
The rumors began as whispers, passed over garden fences and in the market square of the small German town of Leonberg. They clung to Katharina Kepler like the scent of the herbs she grew and sold. At 68, she was a widow, sharp-tongued and unafraid of a dispute. She was the mother of the famous Imperial Mathematician, Johannes Kepler, a man who conversed with emperors and charted the paths of planets. But in Leonberg, in 1615, she was simply an old woman who made people uncomfortable. It started with a neighbor, Ursula Reinbold, the wife of a glazier, who claimed a bitter drink from Katharina’s hand had given her a chronic illness. Then a 12-year-old girl said a passing touch from Katharina had filled her arm with a pain so intense she couldn’t move her fingers. Soon, the stories multiplied, each more fantastic than the last. She had appeared through locked doors, they said. She had ridden a calf to death. One of her own sons, Heinrich, spoke of a roast made from the enchanted animal. The whispers curdled into formal accusations. Lutherus Einhorn, the town’s Vogt, or chief magistrate, was a man with a history; he had already presided over the burning of eight other accused witches. In the fertile ground of local fear and superstition, the case against Katharina Kepler took root.
In Linz, where he served the emperor, Johannes Kepler received the news with a cold dread. His mother, the woman who had first shown him a comet streaking across the night sky, was formally accused of witchcraft. This was not an abstract problem of celestial mechanics; this was a matter of flesh and blood, of fire and public execution. Of the tens of thousands accused of witchcraft in Europe, nearly half were executed in the German lands, and three-quarters of those were women. The danger was terrifyingly real. For six years, the ordeal consumed him. He was at the height of his career, a man who used logic and observation to decode the heavens, but now he had to apply that same intellect to a battle against hearsay and malice. He uprooted his own family, set aside his groundbreaking work on the laws of planetary motion, and traveled back to the world of his childhood, a world steeped in fears he had tried to escape. He did not immediately rush to his mother’s side; instead, he began his defense from a distance, writing meticulously crafted petitions to the Duke of Württemberg. He acted as her lawyer, a role for which he had no training but for which his mind was uniquely suited. His brother Christoph withdrew his support, and his sister Margaretha was unable to leave her own family. The fight fell to Johannes. He knew this was not just a legal contest. It was a clash of worlds: his world of emergent science and rational inquiry against the old world of magical thinking and communal fear.
On August 7, 1620, the authorities arrested 73-year-old Katharina Kepler. They chained the elderly woman to the floor of a prison cell, with two guards watching her day and night—the costs of her own incarceration, food, and heating to be paid by her family. For fourteen months, she endured this humiliation, a prisoner of rumor. When the trial finally began, Johannes Kepler was there, standing beside her. He insisted that all proceedings follow a strict formal procedure, demanding that every piece of testimony be presented in writing. This was his arena. Words on a page could be dissected, their inconsistencies laid bare. He took the 24 witness statements and dismantled them one by one. He argued that Ursula Reinbold’s illness was not from a magic potion, but from a medical condition, offering rational explanations. He showed how the supposed magical pain in the young girl's arm could be understood through common sense and knowledge of the human body. He didn't argue that witches did not exist—a dangerous, and in that era, untenable position. Instead, he deployed a "pioneering defense," a "rhetorical masterpiece," arguing with unassailable logic that the specific accusations against his mother were baseless, the product of personal vendettas and fearful imaginations. He spotted contradictions, questioned motives, and forced the court to confront the sheer flimsiness of the case against a woman whose only crime, it seemed, was being old, outspoken, and knowledgeable about herbal remedies.
The court, however, had one final, brutal tool. They brought Katharina to the torture chamber. It was a tactic of terror, designed to break the spirit and extract a confession where evidence failed. The instruments were displayed to her, their grim purpose explained in detail. This was the ultimate test of her will. Confession meant a quicker death by burning; continued denial, in the face of such a threat, was an almost unimaginable act of courage. Katharina Kepler did not confess. She held to her innocence, her resolve unshaken even in the face of legally sanctioned terror. Her son's logical defense had given her the foundation, but in that dark room, her survival was her own. A week later, in the autumn of 1621, after 405 days in chains, she was absolved of all charges and released. But the victory was a hollow one. The trial had bankrupted her and her son. Her health was broken. The authorities forbade her from returning to her home in Leonberg, the community so thoroughly poisoned against her. Just six months after winning her freedom, Katharina Kepler died. Johannes never spoke of the ordeal to his colleagues; the stigma was too great. The man who had charted the harmony of the spheres had spent six years of his life in a fight against the discord of human fear, and the silence that followed was the sound of its cost.