Quick answer: A decumbiture chart was cast for the moment a patient "took to bed," and the physician watched the Moon move to its critical days, roughly every seventh day, to judge when an illness would turn. The idea runs from Hippocrates and Galen to Culpeper.
An acute illness has a rhythm. It rises, breaks and settles, and the old physicians believed those turning points fell on a schedule they could read in advance. The tool was the decumbiture, a chart of the sickbed, and its clock was the Moon.
Taking to Bed: The Decumbiture
The word decumbiture comes from the Latin for lying down, and the technique is simple to describe. When a patient fell ill and took to bed, the astrologer-physician noted the exact moment and cast a chart for it, much as one would cast a birth chart for a nativity. This "chart of the disease" was then read for the nature and course of the illness, with the Moon standing as the chief significator of the body and its changing state. Alongside it a physician might weigh the sixth house of health, the classical house of illness.
The Critical Days
The doctrine of critical days is older than astrology's part in it. Hippocrates, in the Aphorisms and the Prognostic, taught that fevers come to a crisis on fixed days, the seventh, the fourteenth and the twentieth chief among them, when the disease would either break or worsen. Galen devoted a whole work, On Critical Days, to explaining why, and he tied the rhythm to the Moon. As the Moon moved a quarter of the way around the zodiac from where it stood at the decumbiture, about every seven days, it reached an angle to its own starting place, and that angle marked a crisis.
| Moon's angle to its decumbiture place | Approx. day | Reading in the tradition | | --- | --- | --- | | Square (90 degrees) | Day 7 | First critical day, a turning point | | Opposition (180 degrees) | Day 14 | Second and major crisis | | Square (270 degrees) | Day 20 to 21 | Third critical day | | Return (360 degrees) | Day 27 to 28 | The Moon completes its round |
The Moon's Quarters and the Fever
The logic joined Hippocratic observation to astrological aspect. The malefics and benefics mattered at each crisis: if the Moon, arriving at a critical angle, met a supporting aspect from Jupiter or Venus, the physician looked for a good turn, and if it met Saturn or Mars, he feared a bad one. Watching the phases of the Moon in the sky was part of the same sensitivity to lunar rhythm that governed the whole method.
Culpeper's Decumbiture
The technique reached English readers through Nicholas Culpeper, whose Astrological Judgement of Diseases from the Decumbiture of the Sick appeared in 1655. He set out how to cast the figure for the moment of taking to bed, how to find the significators of the disease, and how to follow the Moon to the critical days for the "judgement." His work is the fullest late statement of a tradition that also produced the calculated health point, the Part of Sickness.
A Rhythm, Not a Verdict
At its best the method was a way of paying close attention to the natural arc of an acute illness, the same arc modern medicine still describes when it speaks of a fever breaking. The astrology added a calendar of expectation and a language of better and worse days. It never claimed to cure; it claimed to read the timing, and even that it held loosely, always alongside the physician's own watching at the bedside.
Frequently Asked Questions
What is a decumbiture chart?
It is a chart cast for the exact moment a patient took to bed with an illness, read like a nativity for the disease. The Moon served as the main significator of the body, and the physician judged the nature and likely course of the illness from the figure.
What are the critical days?
They are the days on which an acute fever was expected to reach a crisis and either break or worsen, the seventh, fourteenth and twentieth chief among them. Hippocrates described them from observation, and Galen tied their rhythm to the Moon's motion through the zodiac.
Can a decumbiture predict recovery?
No. Classical physicians held it as a timing method, not a prognosis. It was read as a calendar of expectation for an acute illness, always weighed against the physician's own watching at the bedside.
Explore the Tradition
To see how the Moon and the sixth house are read in a chart, cast a free birth chart or study your constitution through a health report, which works from classical temperament rather than fortune-telling. For more traditional technique explained plainly, browse the blog.
