Triplicity
Triplicity groups the three signs of one element, for instance Aries, Leo and Sagittarius for fire. To each of these trios, traditional astrology assigns ruling planets, often distinct depending on whether the chart is diurnal or nocturnal. Triplicity is one of the minor essential dignities: a planet placed there gains a moderate support, less marked than in domicile or exaltation.
Three signs, one element
The twelve signs sort into four elements, and each element gathers three signs: that is triplicity. Fire links Aries, Leo and Sagittarius; water links Cancer, Scorpio and Pisces. This elemental kinship explains why signs far apart in the zodiac often recognize in each other a shared way of being in the world.
Rulers according to the hour
Tradition assigns each triplicity a day ruler, a night ruler, sometimes a third called participating. A planet set in its element thus receives a quiet support that adds to the other dignities. In your chart, noting a planet's triplicity refines its reading, giving it a little more or a little less grounding.
Sources
- , Carmen Astrologicum (1st century)
- , The Houses: Temples of the Sky (1998)