Science, Satan, and the Complications of Univocity: Cotton Mather’s Role in the History of Science

| By and (guest author) on Reading the Book of Nature

Introduction by Ted Davis

Everyone knows that Cotton Mather was involved with the infamous Salem witch trials, but not everyone knows the rest of the story. We’re pleased to offer another column byRick Kennedy, author of The First American Evangelical: A Short Life of Cotton Mather (2015). This one is about Mather’s involvement in that episode. As Professor Kennedy explains, we cannot fully understand the controversy surrounding the testimony at trial, without knowing something about René Descartes’ theory of vision, which I explain with images below.

It’s worth pointing out that the trials took place in 1692, nearly at the end of the Scientific Revolution that is so often assumed—quite wrongly—to have put a full stop to belief in the efficacy of witchcraft. In fact, many leading scientists of that period believed that Satan or angels (both good and bad) could communicate with humans. For example, Robert Boyle’s name first appeared in print when a letter he wrote to the Huguenot minister Pierre du Moulin was published as the preface to Moulin’s English translation (done at Boyle’s request) of a book about demons by another Huguenot minister, François Perreaud.

The next words you read are those of Rick Kennedy.

T.H. Matteson, Examination of a Witch (1853), Peabody Essex Museum, Salem, Massachusetts.


Cotton Mather, Univocity, and Satan

In a white paper for BioLogos called “Come and See: A Christological Invitation for Science,” Mark Noll wrote of two long traditions of scientific thought among Christians. One tradition found a watershed in the writings of Thomas Aquinas. Even though he was optimistic about all matters of human inquiry, Thomas kept scriptural revelation distinct from human authorities and human thinking.  The Thomistic tradition, when push-comes-to-shove, emphasizes Isaiah’s “my thoughts are not your thoughts/”your ways are not my ways” sense of disjunction between us and God.

The other tradition emphasizes the image of God infused in humans, the connectedness between God and humanity, and the harmonizing that is possible between divine revelation and human knowledge. It emphasizes something called “univocity,” a deep sense of mutual understanding between humanity and God. This tradition found an early watershed in the writings of Duns Scotus and has encouraged science’s confidence that it is right. Noll asserts that the Scotist tradition leads into our dominant modern view of the power of human sciences.  

In his essay, which is drawn from his book Jesus Christ and the Life of the Mind [pdf], Noll notes how Cotton Mather played a role in helping extend the univocity tradition into the rise of early modern science. He says,

In the late seventeenth century, … natural theology became a major enterprise when the earlier assumptions — metaphysical univocity and harmonization of the “two books”—encountered rapidly expanding knowledge about the physical world…. In response to this challenge, savants like Cotton Mather in the American colonies (The Christian Philosopher [pdf], 1721) and William Derham in England (Physico-Theology, 1713) offered elaborate explanations for how the structures of the physical and animal worlds revealed God’s purposes in creating things as he had made them.

Noll is certainly correct about the influence of Cotton Mather’s book The Christian Philosopher. However, Mather’s role in this tradition is complicated by his lively belief that Satan is a deceiver who likes to sow confusion. Whatever univocity exists between God and humanity, Mather insisted that one should never allow one’s self to be seduced into thinking that demons are not out and about working their wiles. Lucky for us, Mather affirmed, God sends angels to guard us. Therefore, although Mather does generally encourage the univocity tradition of science into its next phase, he more specifically taught a lively sense of univocity mitigated by demons and angels. This is important because, though the history of scientific methods has often considered notions of a divine revealer communicating to humans, it has not often taken into account beliefs about an active deceiver.

I will pick three small instances to illuminate Mather’s mitigated sense of univocity: his thoughts on epilepsy, his experiments on a demon-possessed girl, and a comparison of Mather’s view with the more clear-cut univocity of his time exemplified by Thomas Brattle and the judges in the Salem witch trials.

Angels and Epilepsy

Epilepsy, Mather wrote in The Angel of Bethesda: An Essay Upon the Common Maladies of Mankind, is indicated when the body is thrown to the ground in convulsions, “eyes distorted, the mouth perhaps foaming, the face with an aspect full of agony.” Mather recommends several medicines that might work to calm the afflicted. Otho T. Beall rightfully titled his book, Cotton Mather: The First Significant Figure in American Medicine (1954), and Mather’s clear-eyed view of epilepsy as a natural condition contributes to Beall’s view. On the other hand, Mather went on to write that sometimes “rational spirits of the invisible world” can “strangely insinuate themselves into the malady.” Good angels and bad angels find epileptics to be ready receivers of their communications. Watch out! Be wary! Epilepsy can be something far from simply natural. It can be from God and be used by God to reveal truths, but Satan might also use an epileptic fit to proclaim falsehoods or twist a truth. The epileptic, himself or herself, should pray: “My God, save me from diabolical illusions.  Let no devil now play and prey upon me!”

Statue of Hippocrates (ca. 150 BC), Archaeological Museum of Kos, Greece. The Hippocratic treatise titled On the Sacred Disease, is about epilepsy—which was widely seen as a divinely caused disease at the time. A very early example of methodological naturalism, the work opens by rebuking those who would attribute the cause to the gods, thus hiding their own ignorance of the real cause, like “quacks and charlatans.” Although Mather believed that epilepsy had natural causes, at the same time he thought God or Satan could use epileptics to communicate truths or falsehoods.

When four years before the Salem witch trials, some children in Boston were afflicted with epileptic-type seizures and contortions, it was decided by a gathering of ministers, doctors, and community leaders that they were demon possessed. Community prayer eventually led to their healing, but not before Cotton Mather and his young wife, Abigail, took one of the girls into their home in order to regularize her diet, sleep, and social life. While she was in his home, Cotton Mather began to experiment on her to learn about demons. Cotton’s first “experiment” was to test whether Martha could read the Bible while being possessed. The answer was no. “If she went to read the Bible her eyes would be strangely twisted and blinded.”  What if someone tried to read the Bible in the same room, but out of her sight? No. She would “be cast into terrible agonies.” Visitors would arrive, and Cotton would perform his “experiments” for them. Could she read the Westminster Catechism? No! It sent her into “hideous convulsions.” Could she read a popish [Roman Catholic] book? Yes!  

Cotton knew that his experiments were inconclusive. He noted that his reading experiments were not really good tests for what demons actually could and could not read. It was a “fanciful business” that yielded only indicators and possibilities. Cotton recognized that Satan was a deceiver and might, in fact, be playing with Cotton’s own brain. “What snares the devils might lay for us” in such experiments.  Cotton Mather was seriously engaged with healing a girl and studying demons, but his seriousness was not without wariness. As much as he was he was studying demons, he knew that the demons might be twisting his thoughts in wrong directions.

Witchcraft and the New Science: How Does it Work?

During the trials, Cotton Mather and many other ministers believed that the judges should be very careful not to find themselves caught up in Satan’s traps. Eventually he and most of his colleagues concluded that Satan did actually win in Salem—confusion reigned. One instance of this confusion was a disagreement about courtroom use of Cartesian scientific theories of sight (see the illustration). We know about this confusion from a letter, written by Thomas Brattle to the judges. A schoolmate of Cotton Mather, Brattle was well-known in Boston society as a wealthy bachelor devoted to the study of astronomy and mathematics. After graduating from Harvard, Brattle lived for five years in England where he socialized with famous men of science, especially Robert Boyle. When Brattle returned to Boston in 1689, he resumed a Boyle-like existence as Boston’s pre-eminent scientific thinker. In 1692 he was well placed in society to comment on the science being used by the judges in the Salem Village courtroom.

René Descartes’ theory of vision, from an eighteenth-century edition of his posthumously published Treatise of Man (L’homme de René Descartes, 1729). Descartes believed that light was a motion transmitted through a medium, not unlike a “wave” generated by the crowd at an athletic event. The medium consisted of tiny particles of what he called “the second element,” roughly equivalent to the classical idea of the “aether.” The pressure produced by those moving particles, when they impinged on the retina of the eye, produced the sensation of vision. On the basis of this theory, Thomas Brattle denied that anyone could genuinely “see” when their eyelids were shut, thus blocking the motion from reaching the retina

Brattle did not like what he heard about the judge’s use of the “doctrine of effluvia.” Sharp tongued, Brattle criticized the court’s mis-application of what was a major scientific theory of the era as evidence for a witch’s use of an “evil eye.” In the courtroom, an afflicted girl was sometimes cast into a fit when she looked into the eye of an accused witch. When this happened, the judges then asked the accused to touch the writhing girl. Upon being touched, the girl became calm. Brattle sarcastically wrote that some of the judges were “so well instructed in the Cartesian philosophy” that they declare “how by this touch, the venomous and malignant particles, that were ejected from the eye, do, by this means, return to the body whence they came.”  

Brattle declared, “I must confess to you, that I am no small admirer of the Cartesian philosophy; but yet I have not so learned it.” He accepted the Cartesian scientific theory, but believed that the judges were not applying it fully. Brattle insisted that the Cartesian “doctrine of effluvia” separated spirit and matter, such that no evil spirit could regulate the emission of particles—no witch could turn off and on, nor direct precisely, an evil eye. If a witch’s eye emitted particles that could throw people into fits, then every person who looked into the witch’s eye should have been thrown into fits—not just the afflicted girl.

One of the most important creators of modern scientific methods, the English chemist Robert Boyle carried out numerous experiments on “effluviums,” material particles of “wonderful minuteness” given off by certain solid bodies and diffused through air in “steams” or in water as a tincture. In a particularly memorable instance, Boyle suspended a lump of asafoetida for 5½ days. Despite the fact that he did this during a cold spell, it still “had about it a neighbouring Atmosphere replenish’d with foetid exhalations,” yet he found “no discernable loss of weight” in the original lump (The Works of Robert Boyle, vol. 7, pp. 233 and 248).

Brattle went further by insisting on another matter involving the mechanical philosophy of late seventeenth-century Britain. The judges accepted as evidence statements from the girls about seeing specters when their eyes are shut. Brattle declared that “the thing, in nature, is an utter impossibility.” According to mechanical philosophy, sight is caused by particles either entering or putting pressure on the eye. It is impossible for girls to see specters with their eyelids shut. Particles are blocked by the eyelids, and so what the girls were not “seeing” anything.

If we accept Mark Noll’s generalization that the univocity tradition was encouraged by Cotton Mather and others in the late seventeenth century, then in these three examples we can see something distinctly different separating Mather from Brattle and the Salem judges. Mather was humbled by his belief in deceivers. Brattle and the judges, however, fought with each other with the rather pompous assurance that proper scientific knowledge would lead to truth. Brattle also believed he could declare something “impossible”—a sure sign of univocity. Mather, on the other hand, was anxious to push his mind as far as it would go, but like C.S. Lewis when writing The Screwtape Letters, he was convinced of the need for caution. The pursuit of science, for Mather, is not simply a matter for humans in a univocal relationship with God. Satan is an active and persistent deceiver.




Davis, Ted. "Science, Satan, and the Complications of Univocity: Cotton Mather’s Role in the History of Science" N.p., 24 Jun. 2015. Web. 19 February 2019.


Davis, T. (2015, June 24). Science, Satan, and the Complications of Univocity: Cotton Mather’s Role in the History of Science
Retrieved February 19, 2019, from /blogs/ted-davis-reading-the-book-of-nature/science-satan-and-the-complications-of-univocity-cotton-mathers-role-in-the-history-of-science

About the Authors

Rick Kennedy

Rick Kennedy received his BA, MA, and Ph.D. from the University of California, Santa Barbara and is professor of history at Point Loma Nazarene University, San Diego, California. His books include A History of Reasonableness: Testimony and Authority in the Art of Thinking (University of Rochester Press, 2004), Aristotelian and Cartesian Logic at Harvard (Colonial Society of Massachusetts and University Press of Virginia, 1995), and Faith at State: A Handbook for Christians at Secular Universities (InterVarsity, 1995).

More posts by Rick Kennedy

Ted Davis

Ted Davis is Professor of the History of Science at Messiah College. A former high school science teacher, Ted studied history and philosophy of science at Indiana University, where his mentor was the late Richard S. Westfall, author of the definitive biography of Isaac Newton. With the English historian Michael Hunter, Ted edited The Works of Robert Boyle, 14 vols. (London: Pickering & Chatto, 1999-2000), but his interests include the whole 2000-year interaction of Christianity and science. Author of dozens of scholarly articles and essays, Ted is one of few historians who have written extensively about both the Scientific Revolution and modern America. He and his wife Kathy enjoy theater, music, and traveling to new places.

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