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A mutable sign is an astrological sign that can be adjustable, understanding, analyser, extrovert. The sign that comes under the mutable section can be associated with the positive qualities as it can act on any sides of Cardinal as well as the Fixed signs. The mutable signs are:
Gemini () : between the spring and summer seasons.
In a Byzantine scholium to Chapter 2 of the Introduction to astrology by fourth-century late Roman astrologer Paulus Alexandrinus, the following clear definition can be found:
"A double-bodied zoidion [sign] is said to be between two seasons, such as Gemini between spring and summer, ending the spring and beginning the summer [...] That is to say, double-bodied as being between the two bodies of spring and summer."
900 years later, when medieval Italian Guido Bonatti wrote his Liber Astronomiae, in the final years of the thirteenth century, the definition remained the same and his is more verbose:
"The moveable (cardinal) signs are so-called [...] because at the time when the Sun enters them the disposition of the air is changed [...] The common signs are so-called because when the Sun enters any of these signs it makes the time common, neither truly fixed nor truly movable, but it partakes of both, fixed and moveable. Whence part of that time it is of one [nature] and part of the other [...] when [the Sun] leaves Leo and enters Virgo, then the season is changed, and is made partly summer and partly autumnal."
^Paulus Alexandrinus. "Introductory Matters."" Text as translated by Dorian Gieseler Greenbaum in Late Classical Astrology: Paulus Alexandrinus and Olympiodorus. ARHAT Publications (Archive for Retrieval of Historical Astrological Texts) (Reston, VA; 2001.) P. 5.
^Guido Bonatti. Liber Astronomiae. [translated by Robert Zoller] Project Hindsight. The Golden Hind Press. (Berkeley Springs, WV, 1994.) Second tractate, Chapter XI. (Vol. 2, p. 2.)