In astrology the term quadruplicity is used to refer to the grouping of certain signs into sets of four, which are thought to share the same quality.
There are three “quadruplicities”, which are also known as “modalities”:
The cardinal signs are: Aries, Cancer, Libra, Capricorn. These signs constitute the cardinal quadruplicity.
The fixed signs are: Taurus, Leo, Scorpio, Aquarius. These signs constitute the fixed quadruplicity.
The mutable signs are: Gemini, Virgo, Sagittarius, Pisces. These signs constitute the mutable quadruplicity.