How do you defend a witch? It is often assumed that Johannes Kepler, the defender of Copernicus’s sun-centered universe, the man who discovered that planets move in ellipses and who defined the three laws of planetary motion, simply met ‘irrational’ claims of witchcraft with Enlightenment scepticism. In fact, modern distinctions between the rational and irrational – religion and magic – obscure how knowledge about humans and nature mattered equally to him and many of his contemporaries.
So, if not a straightforward refutation of witchcraft, what then? To understand the genius of Kepler’s defence, we need to understand the prosecution. At this time in England, James I advocated trial by dunking (famously, drowning proved innocence). Nonetheless, the notion that even a witch deserved a ‘fair’ trial remained important.
That meant, for example, that an accused woman, whatever the crime, could not speak for herself – she required a man to speak on her behalf – and that women alone were not considered to be reliable witnesses. It also meant that evidence of witchcraft that occurred after an accusation had been made could not be included. For an accusation in Katharina’s home territory of Württemberg to be legal, a successful prosecution required not just the authority of the ducal governor, but also the duke himself, his Stuttgart chancellery and the professors of law at Tübingen University. Witness interrogations and the prosecution and defence cases were heard locally and then transcribed and delivered to the authorities for judgement.
Consequently, a successful prosecution depended on its meeting the requirements of the Imperial Law Code. By contrast, an effective defence required Kepler to discredit every single witness through legal reasoning. In addition, Kepler insisted that a particular procedure, developed in Roman Law, was to be used – meaning that all documents had to be presented in writing. This was a stroke of genius – it fully informed the defence about the evidence and, critically, enabled Kepler to mount a defence founded in the use of the tools of his intellectual life: textual scrutiny.
The fact-orientated inquiry of ‘things themselves’ was increasingly championed in all intellectual fields. Kepler’s education had nurtured his patience for puzzling over specifics. He had closely combed through literary and scholarly texts all his life, encouraged by the humanist devotion to meticulous philological analysis as well as a new Mannerist delight in keeping the mind flexible through enigmas, riddles, hidden jokes, intricate conceits and allegorical word play.
This had trained Kepler to attend to details and contradictions in the testimonies, a skill he had also honed in refuting scholarly opponents. The new taste for experiments and observations taught him how to assess who was doing the thinking, with what kind of authority and intentions, in a particular case, to produce what kind of data. If history and philology were needed to evaluate data presented by ancient writers, sociological context was needed to evaluate contemporary scientific arguments about singular natural phenomena, such as comets.
Kepler rigorously interrogated testimonies to establish which might be reliable. It mattered to any natural philosopher whether someone who observed, say, orbits, was female, socially marginal, self-interested and known for major moral shortcomings, or, by contrast, male, possessed of a solid social status and was long-experienced in particular areas of knowledge. Such insights from the human sciences and legal hermeneutics forged in antiquity had become just as important in natural history, and explain why leading minds took care to appear authoritative in the impression they made on others through observing etiquette and decorum.
In their actual writing, good natural philosophers then drew on legal methods to argue persuasively about who deserved to be trusted. They tried to end fruitless controversies about what was true or not in tricky matters by reaching a consensus about reasonable conclusions. These methods “bound science to scholarship and mathematics to letters”. This was why Kepler not only read the documentation in his mother’s case but also listened attentively to her in prison, as she described how it was normal to act in her world, how a Leonberg widow did widow-like things. Kepler did not descend from an elevated life of the mind to dirty details of a criminal trial. Years of arguing his case in science had prepared him to mount an exceptionally effective defence based on demonstrating that his mother’s reported behaviour was not witch-like but widow-like, on identifying who was a reliable witness and who was not, on clarifying the exact sequence of cause and effect – on, in other words, examining and testing every single item of the prosecution’s evidence.