House division
Whole-sign houses are Hellenistic (1st c. BCE); the quadrant systems are medieval and early-modern
The earliest houses were whole signs — the entire sign rising is the first house — the primary system of Dorotheus, Valens and Firmicus Maternus. (Ptolemy says almost nothing about houses and is usually read as equal house.) Whole-sign dominated from roughly the 1st century BCE until the mid-9th century CE, when astrologers in the Arabic tradition began dividing the quadrants topically. Placidus is named for Placidus de Titis (born 1603), but the semi-arc method behind it is older — Magini published semi-arc tables in 1604, the year after Placidus was born — and it reached English readers through Manoah Sibly's 1789 translation.
What it measures
A division of the local sky into twelve arenas of life. Quadrant systems (Placidus, Koch, Regiomontanus, Campanus, Alcabitius, Porphyry) anchor houses 1/4/7/10 to the horizon and meridian and split the arcs between them by different geometric rules; whole-sign and equal need only the Ascendant.
Where practitioners disagree
- How are the houses divided?
Placidus (the common modern quadrant system), whole-sign, equal, Koch, Regiomontanus, Campanus, Alcabitius or Porphyry
Traditional and Hellenistic astrologers increasingly prefer whole-sign; each quadrant system trisects the space differently.
This engine: Placidus by default, all of the above selectable. - What happens near the poles?
Quadrant systems break down at high latitude — some degrees never cross a house cusp — while whole-sign and equal stay defined
Whole-sign and equal are robust because they need only the Ascendant; the Ascendant is itself latitude-dependent, so placements still change with latitude.
This engine: We fall back to Porphyry when a quadrant system fails, and say so on the chart.
Sources
- Robert Hand, Whole Sign Houses: The Oldest House System
- Chris Brennan, Hellenistic Astrology: The Study of Fate and Fortune (2017)