A house division system dividing each quadrant into three equal parts, based on the Ascendant and Midheaven.
Definition
The Porphyry house system is a quadrant-based method of dividing the astrological chart into twelve houses. It begins by calculating the distance between the Ascendant and the Midheaven (10th house cusp) and dividing this arc into three equal segments. The same method is applied for the arc between the Midheaven and the Descendant, and then the Descendant to the Imum Coeli (4th house cusp). This creates twelve houses of varying sizes, depending on the latitude of the chart's location. Porphyry’s system is valued for its simplicity and for being a bridge between the equal house system and more complex quadrant-based systems like Placidus. It is especially useful in psychological astrology, where emphasis is placed on the relative weighting of house placements rather than strict mathematical accuracy.
In a chart
In a natal chart using the Porphyry system, look for house cusps that divide the chart quadrants into three equal arcs. Unlike Placidus, house sizes remain proportional but may still vary depending on latitude. Ignore extreme discrepancies in polar regions, where this system becomes less practical.
Examples
- In a chart for 40°N latitude, the 10th house cusp falls at 20° Virgo using Porphyry.