Critical Days

Definition

In pre-modern medical astrology, critical days are the days after an illness begins when the moving Moon forms an exact angle back to where it sat at decumbiture — the moment someone fell ill. These were seen as crisis points, when the disease might turn a corner, worsen, or break. The schedule follows the lunar quarter cycle: the seventh day brings the first square, the fourteenth the opposition, the twenty-first the second square, the twenty-eighth the Moon’s full return. The idea grew out of the clinical observation of Hippocrates and Galen, reaching Renaissance medicine via Arabic and Latin practice.

In Tradition

Across the medical-astrology tradition from the Hellenistic period through its Arabic-medieval and early-modern Western reception, critical days were read as the turning points in a sudden illness, timed to the moving Moon’s angles back to its decumbiture position. The thinking was that the illness runs a roughly rhythmic course tied to the Moon’s quarter cycle, and that treatment works best at these crisis points. We keep this as historical reference, not as health advice.

In Practice

The astrologer finds where the Moon sat at decumbiture, then tracks the moving Moon’s later angles back to that point. The main crisis days fall at about seven days (the first square), fourteen days (the opposition), twenty-one days (the second square), and twenty-eight days (the Moon’s return); the gentler angles in between — the sextile and trine — count as lesser crisis points. At each one, the kind of angle and which planets the Moon is then joined to were read for how the disease would go. In the historical framework, treatment was placed on the crisis days, and herbs were chosen from the planetary-rulership tables of Culpeper and Cornell.

Historical Origin

The critical-day doctrine comes from the Hippocratic corpus and Galen, carried forward through Hellenistic medical astrology and the Arabic-Latin medieval reception. Abu Mashar’s Great Introduction (Lean P3) preserves a cluster of critical-day material attributed to Galen. Holden (Lean P10) gathers the early-modern Western way of reading a decumbiture. Lilly’s Christian Astrology (1647, public domain) gives the chief seventeenth-century English account; Culpeper’s Complete Herbal (1652) supplies the herbal correspondences; and Cornell’s Encyclopedia of Medical Astrology (1933) provides the modern Western consolidation.

Etymology

Origin: Greek. Meaning: From kritikos (able to judge, decisive) — days when the illness reaches a judgment point.

Further Reading