The zodiac signs fall under 3 groups according to the seasons of the year.
Cardinal signs are related to the beginning of a season of the year. Fixed signs to the middle of a season, and mutable signs to the end of a season.
These groups are called ‘modalities’, ‘ quadruplicities’, or ‘ qualities’.
Cardinal signs begin, in the astrological chart, at the same time a season of the year is beginning. And that is why they have the tendency to be initiators, they like to begin something new, to put things in motion.
Fixed signs are right in the middle of a season. They tend to keep things as they are, and perfect that which was already initiated. For that, fixed signs have the ability to concentrate, to be determined, and patient.
Mutable signs are the ones coinciding with the end of a season. Mutable means change, and the signs associated to it are the most flexible, versatile, and adjustable signs in the zodiac.
You will find more information on the signs and their modalities, in this short video: Tropical Astrology and Modalities