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 newborn. This "chart of the disease" was then read for the nature and course of the illness. The Moon served as its chief significator, the planet that stood for the body and its changing state. Alongside the chart, a physician might also 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. About every seven days, the Moon moved another quarter of the way around the zodiac from where it had stood at the decumbiture. Each time it reached one of these angles to its starting place, 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 malefic and benefic planets mattered at each crisis. When the Moon reached a critical angle, the physician read the planets it aspected there. A supporting aspect from Jupiter or Venus, the benefics, promised a good turn. A hard one from Saturn or Mars, the malefics, warned of 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 chart for the moment of taking to bed, how to find the planets that signified 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.
