Most people know about the elements in astrology but aren't aware that each one of the four elements; fire, water, earth and air, are different modalities. Meaning, although they are the same element they function differently. The three modalities found across the four elements are cardinal (movability), fixed (sustainability), and mutable ( changeability).
Cardinal signs are signs that kick off the start of each season. Aries kicks off the spring, Cancer the summer, Libra the fall, and Capricorn the winter. These are forceful signs of initiation and change and manipulates their environment. These are the signs that can be found at the head of any project and make great leaders. I associate "movability" to the cardinal signs. In my opinion the cardinal energy is a fast pace moving masculine energy so even the signs of Capricorn (earth) and Cancer (water) may come off as masculine due to their restless energy causing them to always want to produce or be productive.
Fixed signs come after the cardinal signs kick off the new season when the season is in its true energy. Taurus is the fixed sign of the spring after Aries. Leo the fixed sign of the summer following the cardinal sign of Cancer. Scorpio is the fixed sign of fall following Libra. Aquarius the fixed sign of winter following Cancer. Fixed signs like to have things their way and aren't too big of fans of change. They can be stubborn but make solid individuals not easily swayed from their ideals or routines. Fixed signs make great managers because they have a way of keeping everything in order. They're the type of signs to go by a recipe vs just winging it because everything must be precise. They're the planners of the zodiac and offer a great deal of stability.
Mutable Signs, Gemini, Virgo, Sagittarius, and Pisces are the signs that are present when the seasons are ready to transition into the next. These signs have a real unpredictable nature. Mutable means liable to change. People with a lot of mutable energy may come off as unstable or flaky due to their changeable nature, but it's just how they're wired. The mutable energy is necessary so things don't get stuck in routine. They add variety and spice to life. If the Cardinal signs are the CEO and the Fixed signs management, I'd put the mutable signs in the executive or marketing position. These signs are usually visionary and artistic.