Mercury rules both Gemini, an air sign, and Virgo, an earth sign.  Mercury retrograde, an astronomical phenomenon in which the planet appears to be going backward from the perspective of the Earth, is becoming a more common cultural reference point. See Rob Tillett’s excellent article on Mercury retrograde. During Mercury retrograde, the planet’s communication wires get crossed. Many individuals with little interest in astrology beyond their own Sun sign have become aware—through Mercury retrograde, when there is an increased likelihood of communication mishaps —that Mercury rules things like communication and electronics. The Internet, fax machines, and cell phones are all ruled by Mercury.

Mercury is indeed the communication planet, and its placement in the horoscope shows how we communicate with others—and with ourselves.

Mercury is very good at details and things which require technical expertise. This could be anything from accounting to piano playing. It enjoys tinkering and figuring out how things work.

Mercury is also an excellent mimic and can take on the personas of other planets it aspects in a horoscope. Mercury has plasticity. Howard Sasportas writes (in The Inner Planets: Building Blocks of Personal Reality) that, “Mercury represents the archetype that can be any of the other archetypes.”

The mythological Roman Mercury—whose Greek equivalent was Hermes—was associated with music and with mischief. Mercury is the trickster, an archetype with both positive and negative expressions.

He was also the god who was able to travel back and forth between the underworld of Pluto and the upper world of gods and mortals. Thus, Mercury is a planet which allows us to traverse levels of consciousness and experience, to be a messenger within or without. A well-aspected Mercury in the horoscope can describe the potential for disseminating news and information from one level to another—between strata of personal consciousness, work hierarchies, social circles, etc.

Mercury symbolizes intellectual curiosity and enjoys sharing its findings with others. Many journalists, for example, while working in the Jupiter-ruled field of news publishing, are innately Mercurial. Mercury is an excellent student, but often requires no teacher because it values learning for its own sake.

Although Libra and its planetary ruler Venus are most-often associated with being social, Mercury is a planet which enjoys social banter and good, quick-witted conversation. President Kennedy was a Mercury-ruled Gemini who was curious about the world around him and enjoyed a humorous repartee with reporters and others.

Mercury is said (in William Lilly’s classic text, Christian Astrology) to rule bowling alleys and tennis courts, as well as tempests and earthquakes.