Robert Ralley
University of Cambridge

It was beyond question to most early modern Europeans that the heavens influenced what happened on earth. They could see how the lunar cycle matched the timings of sublunar processes such as the tides, and it was a commonplace that the moon affected the growth of living things and the distribution of blood within the human body. Many observers took unfortunate combinations of planets and constellations as portents of disasters such as major outbreaks of plague. The general principle that the heavens affected life on earth was largely uncontroversial. What was contentious was what sorts of influence the heavens had.

Learned medicine as taught in the universities from the Middle Ages onward largely embraced so-called “natural astrology”: the idea that natural processes on earth were driven and shaped by the motions of the heavens. The second century physician Galen, in his discussion of the “critical days” on which a patient’s condition began to improve or worsen, had connected these to the phases of the moon. By the sixteenth century this theory had long attracted criticism, but although it was not universally accepted, the basic connection between heavenly motions and the timings of illnesses and treatments continued to be made in universities and in learned medical practice.

Far more suspect to orthodox philosophers and theologians was the pursuit known as “judicial astrology,” a form of divination. This practice was controversial, disreputable, and increasingly widespread. Judicial astrologers drew figures of the heavens that divided the ecliptic (the sun’s apparent path around the earth) into twelve separate zones, or “houses,” and recorded the positions of the constellations and the planets within them at a particular moment. They made interpretations and predictions based on the complex relationship between these planets, the constellations, and the houses. The moment they chose might be when someone was born (nativities), fell ill (decumbitures), or any number of other events from the beginnings of journeys to financial transactions. It might be the moment at which someone asked a question, in order to provide an answer (horary astrology). Figures could even be cast in advance to work out the best time to do something, such as begin treatment (elections).

geometric scientific drawing
Claude Dariot, A briefe and most easie introduction to the astrologicall iudgement of the starres (London, 1598), sig. N.

Books circulating in print and manuscript laid out complex astrological rules to follow for diagnosis and prognosis. For many years the liveliest transmission of astrological ideas in England was in manuscript, while printed books on the subject were mainly translations of continental works. So we find Claude Dariot in A briefe and most easie introduction to the astrologicall judgement of the starres (1598) advising practitioners that the sixth house revealed the nature of a disease: the constellation there and the planet that ruled over it (and where that planet actually was) would, if read properly, indicate an illness’s qualities. Several decades later, readers of Richard Saunders’s Astrological judgment and practice of physick (1677) were warned that if Venus ruled over the sixth house and was in an unlucky position in the ninth house (just past the mid-heaven) then the physician would be unable to cure the patient and would receive “discredit and ill words” for his pains [p. 59].

There were problems with all this, as theologians and philosophers had pointed out since the Middle Ages. One of the biggest was that claiming to foretell events involving people implied that you did not believe in free will, a central tenet of Christianity. Another was the twins argument: that twins were usually born at nearly the same time but often turned out very differently. In the specific case of medicine, it was also easier to see how a planetary conjunction might cause everyone to suffer the same illness (as in the case of plague) than it was to understand how it could cause a specific disease in one individual, and nothing in others. How could you trace particular effects back to general causes?

Not only divines but also learned writers on medicine attacked the medical use of judicial astrology: they accepted that the heavens could affect people’s bodies, but rejected the knowledge claims of judicial astrologers. In A short discouerie of the vnobserued dangers of seuerall sorts of ignorant and vnconsiderate practisers (1612), John Cotta admitted that there was “a sober and modest vse of Astronomie” in medicine, but described the use of judicial astrology as “trifling vaine idlenesse, foule & vnlearned falshood.”

In the later Middle Ages, however dubious its reputation among theologians, astrology had been a courtly pursuit. Kings had both employed and feared astrologers. The sixteenth and seventeenth centuries saw astrologers attracting an increasingly broad clientele. Particularly as the period went on, numerous practitioners in England used the tools of astrology, alongside other techniques such as uroscopy, to understand the natures and causes of illnesses, patients’ likely prognoses, and the best courses of treatment. Most records of these activities have since been lost, though a few manuscript archives survive wholly or in part: chief among these are the papers of Simon Forman from the turn of the seventeenth century and his protégé Richard Napier, then later on those of John Booker and William Lilly.

Most accessible of all the astrological advice available was that provided by almanacs. These were typically small, disposable pocket books that listed important dates and times, from local fairs and religious festivals to celestial events and when to bathe, and combined them with prognostications for the year to come. Produced annually in their thousands from the 1550s on, they typically included warnings of medical dangers ahead and indications of when to avoid letting blood. It is impossible to know how many of their users relied on their medical predictions to schedule activities or treatment, but their ubiquity is a measure of how widely astrological guidance had become available. Astrology was becoming popular—in both senses of the word. As its reach increased, its status as a branch of knowledge fell.

This may have been due in part to the wholehearted involvement of astrologers in the civil wars of the mid-seventeenth century. For those rebuilding the polity after the Restoration, astrology may have been too closely associated with political radicalism. It had no place in the fledgling Royal Society, even though key practitioners did. There were empirical arguments to be made against it, but most of the attacks it now suffered were fundamentally identical to the criticisms of medieval theologians; the difference was that the social elites who had once depended so avidly on it were now disposed to find those criticisms convincing.

Astrological medicine was still practised in 1700, widely and lucratively; but envy and controversy were being replaced with ridicule and contempt. Belief in astrology would survive, but the days of its widespread practice as a form of medicine for financial gain would soon be over.

Further readings

Chapman, Allan, “Astrological Medicine,” in Health, Medicine and Mortality in the Sixteenth Century, edited by Charles Webster, 275–300. Cambridge: Cambridge University Press, 1979.

Grafton, Anthony, and Siraisi, Nancy, “Between the Election and My Hopes: Girolamo Cardano and Medical Astrology,” in Secrets of Nature: Astrology and Alchemy in Early Modern Europe, edited by William R. Newman and Anthony Grafton, 69–131. Cambridge, MA: The MIT Press, 2006.

Kassell, Lauren, “Almanacs and Prognostications,” in The Oxford History of Popular Print Culture, Volume One: Cheap Print in Britain and Ireland to 1660, edited by Joad Raymond, 431–442. Oxford: Oxford University Press, 2011.

Kassell, Lauren, Hawkins, Michael, Ralley, Robert, Young, John, Edge, Joanne, Martin-Portugues, Janet Yvonne, and Kaoukji, Natalie, eds. The Casebooks of Simon Forman and Richard Napier, 1596–1634: A Digital Edition

MacDonald, Michael, “The Career of Astrological Medicine in England,” in Religio Medici: Medicine and Religion in Seventeenth-Century England, edited by Ole Peter Grell and Andrew Cunningham, 62–90. Aldershot: Ashgate, 1996.