According to Expanding Astrology’s Universe:
The mutable or cadent quality (formerly called “common”) represents different aspects of the mind, so people with a strong mutable emphasis in their horoscopes live a lot in their heads. If they also have strong earth, they will use their minds to produce tangible form in the world, but they will still be highly mental. It is easier for the mind to change and adapt so a mutable emphasis is also associated with flexibility and versatility. Strongly mutable people bend and bend back, they observe the world, seek to understand it, and learn vicariously.
Astrologer Carol Rushman in The Art of Predictive Astrology: Forecasting Your Life Events warns parents of mutable T-square children to be careful of the friends and environments they choose because they’re so chameleon-like and become what they are exposed to. Charles Carter in The Principles of Astrology remarked that the mutable signs often allow others to reap their labors. Also noting that it is regrettable that an apparent understanding of this function has led to them being called flexible or adaptable as if they were time-servers behaving as best suits their purpose. They are in reality active adaptors, not passively adaptable, although the two negatives (Virgo and Pisces) may sometimes be too ready to suit their conduct to their company. They work hard, Gemini to use ideas and words, Virgo to use tools, Sagittarius to explore both intellectually and as an actual traveler, while Pisces adapts colors in painting and expression in the dramatic art. Mutable sign people often show uncertainty and it is unclear what direction they will go.
Donna Cunningham says, Besides being a planet in our solar system and a mythological god, Mercury (Gemini’s ruler) is a metal, and a very peculiar one at that. Tt is liquid form, and doesn’t really behave like water. If you or it out on a table it won’t leave any traces of wetness. Instead, it forms into little silvery balls and runs off in all directions. Mercurial people too, are paradoxically similar to the metal in many ways. Fluid, adaptable, and changeable. They respond quickly to the changes in the social world around them.
They can appear quite sensitive and responsive to other people, it is a very different kind from than what you find in a water sign. Mercurial sensitivity consists mainly of perceiving and comprehending things with the intellect tath than with emotions, which mercurial people sometimes tend to run away from in all directions rather than face them. Another common name for the metal mercury is quicksilver. Both quicksilver and mercurial are words that have been used to describe fast-moving, fast-talking, and ever-changing individuals. The metal runs off in all directions when you pour it, and Mercurians are restless and distractable, with a tendency to scatter themselves. But scattering doesn’t;t hurt the metal mercury nor does it seem to hurt mercurial people – they have the ability to bring all these scattered bits of data together and make connections between them, just as droplets of mercury readily coalesce. Then, too, going off in all directions is one sure way not to get stuck in the mud! The metal mercury readily takes on the shape of the things it comes into contact with. Dip a dime in mercury and adheres to all the little grooves and surfaces.
Many mutable sign people are learners and teachers. The mutable signs relate to our mental attitudes and are concerned with ideas; they are adaptable, changeable and are usually related to writers, journalists, and publishers. Astrologer Charles Carter and author of the book: Essays on the Foundations of Astrology, states that a Sagittarius-Pisces square presents much less of a problem, and there is an excess of feeling and sentiment and emotional restlessness. The Gemini-Virgo square produces high mental activity and intelligence, and they also have a tendency to bookishness and seclusion. Carter believes the Virgo-Sagittarius square (ruled by Mercury and Jupiter) is OVERLY critical. Sue Tompkins says the type has a tendency to exaggerate (Sag) other people’s imperfections and perhaps be over-liberal with criticisms (Virgo). The author also asserts that there is a natural skepticism of others’ beliefs, but on the positive side, this combination brings their philosophy of life together with the need to serve and is a good placement for occupations in the voluntary sector and charitable organizations.
The Gemini-Pisces square is another square that some astrologers don’t see as bringing many conflicts to the native. The worst that is said is that the type tends to superficial chatter. Carter says the common signs (mutable) have the possibility of dispelling conflicts in talk and discussion. The unmovable and embedded quality of the usual “complex” is most likely to occur under the fixed signs. A view on the fixed square/s in the horoscope is discussed by Liz Greene The Horoscope in Manifestation: Psychology and Prediction when dealing with complexes. The author emphasized that fixed aspects are the ones that become most ingrained in our personality. This might be due to the immovable nature of the fixed signs, and also the self-pride, stubbornness, and a refusing to budge type of attitude. On the positive side, these people are often the most determined and do not give up easily, usually achieve their goals, as these signs do not let go easily.
On the opposite end of the spectrum, it is supposed that the mutable types are the easiest to get along with, and this is mainly due to these individuals being gifted at adapting to the environment. The only dilemma these individuals face is their over-yielding nature, being too easily side-tracked, and adjusting automatically when perhaps standing and being firm is the better option. The further we delve into astrology and enter into the modes, elements, and general actions of the signs the better understanding we begin to have of ourselves and our own complex natures.
Finally, Charles Carter noted the changeable nature of these types and how this impacts the planet involved:
There is a changeableness characteristic in maps wherein many planets are in mutable signs. The nature of the planets therein, and their house rulerships, determine in what matters mutability will be specially manifest upon the extent and real nature (whether deep or only superficial) of the changeful tendency. Thus Venus in a mutable sign may show affectional mutability; the nature is at one time demonstratively affectionate, at another indifferent. But in an otherwise good soul, this may be rather a question of manner than of real character.