The essence
The modalities (also called qualities or quadruplicities) sort the twelve signs by where they fall in a season. Mutable signs come last: Gemini in late spring, Virgo in late summer, Sagittarius in late autumn, Pisces in late winter, following the Northern Hemisphere seasons the tropical zodiac is built on. Gemini scatters spring's seeds into a thousand conversations. Virgo sorts the summer harvest and decides what gets stored. Sagittarius scans the autumn horizon for meaning. Pisces melts winter's ice back into the sea.
The astronomy is simple. Cardinal signs begin at a solstice or equinox, and mutable signs are the month just before one. The Sun leaves Gemini at the June solstice, Virgo at the September equinox, Sagittarius at the December solstice and Pisces at the March equinox. These are the weeks when one season is already loosening its grip.
Ancient astrologers such as Ptolemy called these the "double-bodied" or common signs, and the images fit: the twins, the two fish, the centaur who is half human and half horse. All four share the capacity to hold multiplicity without collapsing into chaos. They are the editors, teachers and wanderers of the zodiac, the ones who take something from one setting and make it make sense in another.
