Mercury is perhaps the most underrated planet in the natal chart. Astrologers give a lot of importance to the Sun, Moon, and Rising or Ascendant, and even Venus, Mars, Jupiter, or Saturn, but Mercury seems to suffer from neglect. Is this because of its apparently small size(even the glyph is smaller), or the fact that it is difficult to see in the sky(it can only be seen shortly before sunrise or after sunset)? In astrology, as is the case with Pluto, size or even visibility is not always an indication of importance. What matters is if it has an observable impact in the birth chart, and Mercury definitely has an impact. I would say that Mercury is as important as the Sun, Moon, or any other planet in the birth chart. Observations have shown that it has a crucial effect on mental perception or the thinking process. What good is the rest of the chart if it cannot be perceived or used intelligently? The sign or element Mercury is in will show just how that person processes information or relays it back out. It is similar to the Ascendant in that it filters the way you see, view, or understand things. An air sign Mercury will think clearly, quickly, objectively, and idealistically while an earth sign Mercury will think logically, methodically, practically, and much more slowly. A fire sign Mercury will also think quickly or idealistically, but much more personally or passionately than an air sign, whereas a water sign Mercury lets the feelings or emotions color the the thinking process. Masculine Mercurys(fire and air) are louder, quicker, and more confident or outspoken(Gemini side), whereas the feminine Mercurys(water and earth) are more quiet, sensitive, and thorough(Virgo side). Masculine Mercurys make better speakers, lecturers, salesmen, comedians, entertainers, and storytellers, while feminine Mercurys make better researchers, analysts, secretarys, statisticians, writers, and critics. Aspects to Mercury can modify this but the gender rule will always hold. Neptune conjunct, for example, can soften a masculine Mercury, but it will never drown out the basic qualities of the placement. Mercury retrograde can also soften or interiorize the normally extroverted nature of Mercury. In synastry, one person's Mercury to the other person's Mercury is the prime index of mental or communicative compatibility. Other aspects can help or hinder, especially from the Sun, Moon, Ascendant, or Jupiter, but the basic harmony or inharmony is in the Mercury-Mercury comparison. I have also noted basic differences in diet, dress, and philosophy when two Mercurys are very different or incompatible. Masculine sign Mercurys find feminine sign Mercurys too quiet or secretive, while the feminines find the masculines too loud or insensitive. Fire and air stimulate each other as do water and earth. Fire burns water and irritates earth. Earth thinks fire is childish and air is flaky. Air thinks earth is dull or slow and water is too mysterious or emotional, and water thinks fire is too full of itself and air is out to lunch. Signs traditionally ruled by the same sign such as Aries/Scorpio(Mars) or Capricorn/Aquarius(Saturn), will fare a little better but they may still be basically incompatible. One of the most contentious issues in astrology is that of rulership. Every sign has a planetary ruler, and until the modern era, seven planets ruled twelve signs. Sun and Moon always ruled one sign each(Leo and Cancer) but the other five traditional planets ruled two signs each. When Uranus was discovered in 1781 it was soon found to rule Aquarius leaving Saturn to Capricorn and when Neptune was discovered in 1846 it was soon found to rule Pisces leaving Jupiter to Sagittarius. This unfolding continued with the discovery of Pluto in 1930 which was then determined to rule Scorpio leaving Mars to Aries. Only Mercury and Venus are left still ruling two signs each. They will single out when two other planets are discovered or determined as rulers. Long time followers of this site know that I equate planet Earth with Libra working through the Ascendant or Rising sign and Venus to Taurus. Eris is still a question mark as is Ceres or Chiron. Mercury's true ruling sign is still a puzzle to me. Sometimes I feel it is Gemini and other times I feel it is Virgo. I have never been so divided on almost any other issue in astrology. Most would give Mercury to Gemini being a messenger and all, and he does seem to express most strongly and intelligently in the air signs, but a good case can be made for Virgo as well -such as Mercury's fine analytical or discriminatory powers. Mercury is truly one of the last astrological mysteries for me and I hope I can resolve it in my lifetime. When Mercury's true ruling sign is finally determined, and a new planet assigned, astrology will be a lot more complete and so will each of us. This goes for the Venus rulership as well. Everytime a new planet or rulership unfolds so does the human potential. Uranus gives us freedom over bondage(Saturn). Neptune gives us compassion and understanding over quick or harsh judgement(Jupiter), and Pluto makes possible the transformation of our base desires(Mars). The true ruler of Libra will bring worldwide peace and justice over warmongering and possessiveness(Venus), and the true ruler of Virgo will bring physical paradise on Earth by teaching us how to use our mental energies(Gemini) constructively and responsibly and to be in perfect attunement with nature. Mind or thought is a powerful thing as is sound or speech. Both are the underlying fabric of matter and are represented by the planet Mercury. Gemini thinks it and Virgo audifies or manifests it. Whatever thoughts or words you say usually manifest at some point or place in time. In certain regions or planes of our universe thoughts or sounds manifest instantly and it is our goal to learn to use these powers responsibly before we can access those regions. In ancient tradition, Hermes, Enoch, Thoth, or Mercury was an important divinity entrusted with disseminating knowledge and wisdom, enacting commerce and trade, and guiding the dead. He sped to and from the diverse gods(planets) with winged sandals(aerial rudders), Pluto's invisibility helmet(cloaking device), and his trusty cadeuceswhich gave him the power to sway and heal. His youth, charm, intelligence, and versatility made him very popular among both gods and humans and his mischievous qualities were largely tolerated and forgiven. This sounds a lot like Gemini doesn't it? Perhaps Mercury really does rule Gemini first and foremost. Mercury's female counterpart was the godess Isis(Virgo) who served as Hera's messenger. She was taught or instructed by Hermes or Mercury before becoming a truly great godess.