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Cardano’s Demons: Renaissance Demonology and Divination

A cursory glance at his autobiography reveals Girolamo Cardano (1501-1576) to have been a man interested in many - sometimes unorthodox - ways of understanding both the natural and supernatural world. I am particularly interested in how Cardano leverages different scientific methodologies, primarily anecdotal evidence, to support his theories regarding demonology and divination. De subtilitate rerum (1550), Metoposcopia (1550; pub. 1658), and his autobiography De vita propria liber (1576) are texts that encompass two very different periods of Cardano’s life. These texts serve as a lens through which we can better understand the ways that Cardano used evidence from different scientific traditions to support his ideas. Indeed, Cardano’s accounts of the demonic draw on multiple rhetorical strategies and scientific traditions in proving the existence and mechanics of demonic influence.

Cardano’s Renaissance masterwork autobiography, De vita propria liber (“The Book of my Life”), contains two chapters devoted to the supernatural and, by extension, the demonic. These reflections provide a useful culmination of his personal experiences as they relate to his more academic evaluations of the demonic. (Cardano, 2002) He adopted a narrative tone of reflection rather than the analytical accounts he provided in earlier works like De subtilitate rerum. He was very aware of the range of reactions the contemporary reader might have had and used colloquial language like “unloading a wagonful of boards” to describe odd sounds and occurrences, conveying a conversational, informal style. Most of these supernatural events discussed in “On things absolutely supernatural” (Chapter 43) amount to him hearing a loud or repetitive noise, misplacing something, or perhaps having a particularly vivid dream. To Cardano’s credit, he did point to the possibility of a natural cause for many of these happenings (in one case, he seems to refer to a 1559 earthquake). However, I think this should be taken with a grain of salt, as this self-awareness also works as a useful rhetorical strategy for convincing readers of his credibility. Cardano argues for the importance of preserving these experiences as best we can, “nailing them, as it were, upon our consciousness” and concludes with a direct address to the reader by arguing that in the vastness and infinity of the universe, nothing that he has said should be considered beyond belief. This direct appeal to the reader makes a lot of sense, both in the context of the autobiographical format and the systems of correspondence that dominated streams of communication between scientific (especially medical) communities in this period.

Another interesting narrative strategy is the use of the dream sequence. His first-born son, Giovanni, was beheaded in 1560 for poisoning his wife, a death that deeply affected Cardano and his system of philosophy as presented in this text. Describing the devastating impact of the death of his son, he links his grief to a dream in which he is given a gem that allows him to forget about his son. (Cardano, 2002) A few decades later, Johannes Kepler’s Somnium (1593-1634) re-orients the relativity of motion by examining how the phenomenon of the Heavens would look from the surface of the moon, in the setting of a dream. This argument in favor of the Copernican model is buoyed by jokes about the religious and political turmoil of the time, making it a genuinely fun, direct engagement with the reader. (Kepler, 1967) Although Cardano’s tales are presented in a less organized, intentional way than Kepler’s, Cardano was using dreams and visions as a fabricated vessel for getting his points across to the reader.

Cardano opens a later chapter on guardian angles by comparing himself to Socrates (he had a bit of an ego). According to Cardano, they have been watched over by similarly unique guardian spirits. (Cardano, 2002) Additionally, Plotinus, Synesius, Dio, and Flavius Josephus are looked favorably upon by these spirits. Others, who have led dazzling yet evil lives, are supposed to owe their accomplishments in part to an attendant spirit. Among these are Gaius Caesar the Dictator, Cicero, Antony, Brutus, and Cassius. Cardano believed that his guardian spirit warned of his son’s death and is responsible for many of the unexplained occurrences mentioned in his earlier discussion of the supernatural. He makes the distinction that because these experiences are vague, it actually supports the notion of divine guidance, as opposed to more direct visions or warnings. He speaks extensively about why he is worthy of such divine intervention. Additionally, humans are imperfect material through which spiritual premonitions must pass, so reactions will vary widely. He argues that the simplest (and strongest) proof he has for these events is drawn from spiritual inspiration, coupled with an intellectual insight he has cultivated for over 40 years. Not unlike mathematical proofs, which are their "own explanation." Cardano’s argument is strengthened by both natural and divine philosophy and is still humbly left open to the criticism of theologians (his "intellectual betters").

In De subtilitate rerum (“The Subtlety of Things”), Cardano’s chapter "On demons" is generously interspersed with both personal anecdotes and examples of divination from Greek mythology. In these anecdotes, his fascination with the marvelous takes the clearest shape. “On demons” reads like a careful fusion of both Cardano’s natural and supernatural experiences. (Cardano, 2013) Cardano equated the machinations of angels and demons to the movements of the stars, his more scientific, astrological worldview informing his spiritual, demonological one. His account of a woman being inexplicably cured of her “burning urine” is acknowledged to be either the result of a demonic intervention or her “faith and imagination” (the placebo effect). However, despite his incredulity (he often references the possibility of natural causes), he pointed to supernatural accounts by Plutarch and Pliny as evidence in favor of the former, demonic explanation. Cardano references the works of Constantine, such as methods of healing wounds, as “evidence of spells,” and for some, evidence of demonic manipulation, a claim he views with skepticism.

One of Cardano’s most fascinating anecdotes on the demonic comes from his father, Facio. When his father was alive, he recalled the 1491 appearance of seven spectral men claiming to be dead but in the state of existing as neither men nor gods. (Cardano, 2013) They are to us as we are to beasts, engaging Facio in a series of profoundly intellectual and philosophical discussions lasting over three hours. Cardano’s faithful recounting of his father’s demons does take care to leave the event open to interpretations of authenticity. What makes the entire description so odd is the conflict Cardano seems to harbor about it. He writes as if simultaneously convinced that this exchange truly happened yet is completely impossible. This attitude is partly due to Cardano's vastly different personal experiences with the demonic, as discussed in his autobiography. This aversion may also stem from the heretical nature of the specter’s claims about the creation of the earth, rather than his credibility as a natural philosopher. That is, they asserted that God did not actually create earth from eternity and that it is not eternal itself. These assertions, informed by certain texts of Averroes that were not “discovered” until six years after the spectral conversation, added to the mystical nature of this encounter. They likely aided in laying the foundation for Cardano’s conviction that demons are an explanation for some forms of divination.

To illustrate the role of the demonic in divination practices, Cardano drew from both the past (the boy seer for Emperor Didus Julianus) and from around the world (through the eyes of diplomat Leo Africanus). Demons and the dead have stronger connections to climatic events such as human death and natural disaster, and in these instances, are easiest to perceive or contact. (Cardano, 2013) Tales of ancient pagan oracles, whose predictions were inexplicable even to the great minds of Aristotle and Plutarch, are used to further his line of argument. Cardano’s direct references to Arabic divination are limited in this chapter to an account of a man drinking cock’s blood to divine the arrival of winds to a stranded ship. Petrus Aponesis, a Professor of Natural Philosophy at the University of Padua, authored the Conciliator (1476) in an attempt to reconcile Arabic medicine with Greek speculative natural philosophy and is criticized by Cardano for his interest in necromancy. This fault aside, Cardano embraced his notion in his integration of both Arabic and Greek sources and translations.

Cardano's understanding of demonic influence manifested very differently in men as opposed to women. Men were admittedly subject to demonic trickery but are also able to utilize demons as tools of divination. Whether a man uses these tools for pure or evil intent is seemingly at his discretion. Women, however, are presented as lust-filled and highly susceptible to the diabolical. Indeed, for Cardano, only the stupid and the weak willingly accept demonic aid, in this case, for seeing the future. Against the larger backdrop of European witch hunts and the influence of publications like the Malleus Maleficarum (1486) throughout the 16th century, this observation is in line with more widely held beliefs on the nature of witchcraft and the roles of demonic service.

Cardano’s Metoposcopia was published posthumously in Paris in 1658 and pointed to some huge shifts in the perception of demonic influence in the Renaissance. It is a vast and diverse set of volumes that investigated the mind’s various facilities and how they relate both to each other and to angelic or demonic beings. (Cardano, 1658) He focuses on metoposcopy, or physiognomy, which is a form of divination based on the pattern of lines on the subject's forehead. The practice was banned by Pope Sixtus V in 1586, a decade after Cardano’s death in 1576. Cardano is no stranger to controversy, having been arrested by the inquisition in 1570, and this unpublished work includes many contradictions with Christian doctrine. The direct role of the diabolical in human endeavors was becoming increasingly well defined, and Cardano reflects this evolving role of the demonic. He describes the demons that affect our consciousness as possessing individuality, with natural variation occurring in the same way as it does in humans and animals. (Maggi, 2001) He also distinguishes between good and bad demons based on the visions they grant us. In this sense, Cardano positions demons as key players in human intellect. However, he is careful to point out that demons are not actually capable of understanding the world in the same way as people. We are fundamentally different, and this may be a way of appeasing the more traditional tenets of Catholic demonology (although Cardano’s philosophy adds quite a bit to the traditional body of knowledge). Humors also play an important (but not vital) role in his descriptions of demonic manifestations. Indeed, Metoposcopia embodies the complex interplay between Renaissance religion, science, and Cardano’s own unique philosophy.

Visual aids were a critical component of Cardano’s Metoposcopia. Diagrams of human faces and their associated traits made up the bulk of his several volumes on the art of forehead divination. (Cardano, 1658) Cardano was making up a lot of metoposcopy as he went along, building on existing Greek occult physiognomy but adding strong ties to the Zodiac (moles on certain areas of the face were associated with different signs and traits), vastly enhancing the possible range and precision of predictions. To accomplish this, Cardano worked up about 800 facial figures, each associated with astrological signs and qualities of temperament and character. For example, some captions to these figures indicate that long, straight furrows indicate nobility of character or that three curved furrows on the forehead prove one is a simpleton. Most of the diagrams are intended to be broad generalizations, but a few depict specific people (see Fig. 1 for convicted murderers). This creates a strong range of reference images for practicing physicians while accounting for some curiosities and rare outliers. His personal bias also shows in his differentiation of male vs. female heads. A majority of the figures are male and what female faces were available seemed to carry pretty negative associations. He declared that one could tell by the lines on her face which woman is an adulteress and which has a hatred of any lewdness. Where a "noble" brow defines men, women were characterized by their "defiance" or "greed" (see Fig. 2 for women).

These hundreds of facial images are Metoposcopia’s most arresting feature and make it more visually engaging at a glance, but to some extent, they may have contributed to the lack of popularity of Cardano's metoposcopy. Upon close examination, these images are crude, repetitive, and not very empirical. For someone who is practicing this form of divination, it is impractical to have over 800 reference points for separate character traits. Cardano’s images make complex assumptions without doing much in the way of backing it up empirically. Robert Boyle employed a similar tactic with his experiments, meticulously describing every aspect of his work in New Experiments Physico-Mechanicall… (1660), without providing crucial details such as specific, standardized measurements that we would expect in modern experimental descriptions. Instead, he used reference objects, such as paper and lamps, to give the reader some conception of scale. Regardless of the description’s faults, both Cardano and Boyle use virtual witnessing as a scientific tool to bring their experiments and experiences to the learned masses.

Cardano’s empiricism shows up clearly in his extensive studies in astrology. Setting aside Cardano’s more infamous astrological endeavors, like the astrological chart of Jesus Christ (which landed him in some hot water with the Church) and his supposedly perfect prediction of his own death, these accounts more closely resemble Cardano’s use of astrology in the medical context. These astrological charts were how physicians determined the best course of treatment for their patients. They also served an explanatory purpose, as in cases of deformity at birth. As we know from the extensive casebooks of Simon Forman and Richard Napier, astrologers were a popular source of medical advice in Europe. (Kassell et al., 2019) Astrology was a legitimate form of both divination and medical knowledge in Cardano’s time practicing medicine.

Fig. 1 - Convicted murderers depicted in Cardano’s Metoposcopia (1658)

Fig. 2 - Women depicted in Cardano’s Metoposcopia (1658)

Manuel do Valle de Moura’s De incantantionibus seu ensalmis (1620) reveals a Catholic authority’s opinion of demonology in the years following Cardano’s death. (Maggi, 2001) De Moura studied theology at the University of Evora, was the elected deputy of the Inquisition of Evora in 1603, and eventually died there in 1650. An ensalmus (derived from "Psalms") can be broadly defined as any invocative act. De Moura clarifies that “Ensalmi are benedictions or evil invocations composed of a certain formula of words, primarily Holy ones, and sometimes also of material things, like wine or cloth… and many individuals ... make use of these to heal wounds and disease." Nevertheless, as de Moura later claims, these are just words. They have no inherent power and can thus be manipulated by Satan. Language is portrayed as a clean slate, and the end results of ensalmi depend largely on the individual speaking them (ensalmista) and who is listening (God or Satan). Like Cardano’s demons and guardian angels (good demons), de Maura's description of these invocations centers around the demonological paranoia of diabolical manipulation of holy words for the purposes of witchcraft. Like Cardano, the text is full of digressions into specific examples of natural and unnatural ensalmi and can be circular at times, with de Maura backtracking and questioning his own claims. These digressions lead to more traditionally scientific ruminations on the human mind and the nature of diseases, such as melancholia/depression as a form of demonic corruption. They seem to ultimately feed into de Moura's condemnations of women, homosexuals, and heretics, all of whom he viewed as potential agents of Satan. He crystallized the Churches hatred for these groups by articulating how they are perverse both in act and language. These anxieties deeply affect the framework in which scientific practices like astrology and other forms of divination are being done after Cardano's death and continue to be influenced by the posthumous publication of Metoposcopia.

These texts fill out the portrait of a man obsessed with not just different fields of study but many ways of knowing the world around him. His accounts of demonic occurrences are very similar in tone and style to his descriptions of interactions with his patients. Additionally, the scholarship of Greco-Roman and Islamic authors is a clear presence in his digressions. His work strongly corroborates a narrative of cross-cultural transmission that is vital to establishing a context for pre-modern science. Cardano acknowledged the contributions of non-Western scholars, from personal anecdotes to tales of pagan divination from Greek mythology, transmitted by Islamic scholars. Through empirical observation, philosophical and theological rumination, in addition to the use of anecdotal, astrological, and anatomical evidence in his medical practice, Girolamo Cardano has secured an impressive and complex legacy spanning many traditions of human thought.


Boyle, et al. New Experiments Physico-Mechanicall, Touching the Spring of the Air and Its Effects : (Made for the Most Part) in a New Pneumatical Engine. Printed by H. Hall ... for Tho. Robinson, 1660.

Cardano, Girolamo, et al. Metoposcopia Libris Tredecim, Et Octingentis Faciei Hvmanae Eiconibvs Complexa: Cui Accessit Melampodis De Naeuis Corporis Tractatus, Graecè & Latinè Nunc Primùm Editus. Apud Thomam Iolly, 1658.

Cardano, Girolamo. The Book of My Life (De Vita Propria Liber). New York Review Books,


Cardano, Girolamo, and J. M. Forrester. The De Subtilitate of Girolamo Cardano. Arizona

Center for Medieval and Renaissance Studies, 2013.

Kassell et al., ‘A day with the astrologers’, A Critical Introduction to the Casebooks of Simon Forman and Richard Napier, 1596-1634,, accessed 11 March 2019.

Kepler, Johannes, and Edward Rosen. Somnium; the Dream, or Posthumous Work on Lunar

Astronomy. University of Wisconsin Press, 1967.

Maggi, Armando. Satan's Rhetoric : a Study of Renaissance Demonology. University of Chicago

Press, 2001.

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