Mercury rules Gemini, mutable air, and
Virgo, mutable earth, and is said to be
exalted in its own sign, Virgo. By some
it is considered exalted in Aquarius,
where it becomes steadied and humanised.

The basic conception of Mercury is
intercommunication. Hence its rule over
thought and speech and writing, especially
the writing of letters; for the same reason it
rules short journeys and all that ministers to
them, such as roads, bicycles and buses. It
rules trade, which is the exchange of commodities, and
is one of the planets most valuable in business. When prominent, it gives a quick, inquiring mind and ready expression with tongue and pen. There is a strong sense of logic, and a rapid comprehension of facts, often with a taste for detail rather than generalities. It may be a brilliant talker, and often possesses encyclopaedic knowledge. Note that it is not imaginative. Imagination is rather Lunar and Neptunian. It is exact, matter-of-fact, and critical.

Under affliction, the mental powers are seldom lessened, but their may be a tendency to untruthfulness, exaggeration, sarcasm, or ill-temper, according to the nature of the affliction. There may be a liking for hair-splitting or quibbling, too great immersion in detail, or even a criminal misapplication of the mental powers, as in slander, libel or theft. Mercury can never be found in pure form; it is always coloured by sign, house and other factors. As Robert Hand points out, in its pure form it would describe the completely rational and objective mind. A mind free of any distortion or bias, but also free of any kind of moral reasoning too. For Mercury is not concerned with the rights or wrongs of a given situation. The realm of principles, ethic, meaning and morals comes under the umbrella of Jupiter, the planet that rules the signs opposite to those ruled by Mercury.

You cannot always derive the level of intelligence from an astrological chart, but the condition of Mercury will reveal a great deal about the type of intelligence a person has. This is why aspects to Mercury are so important. Mercury in Aries or Gemini gesticulates a great deal; and the planet, unless it is unusually subdued which it sometimes is with Saturn, is naturally very volatile, restless and even merry. Mercury has no emotion, except that it finds great amusement in teasing, in being sceptical or flippant, it is anti-pompous. Mercury is curious, clever, lucid and fluent, and it becomes frustrated if its fluency is inhibited.

While Mercury is shrewd, it is not of itself profound. Writers, though they do not have Mercury in Gemini more then anywhere else, almost always have very active Mercuries. Intelligence is like physical dexterity, which is also Mercurial.
In synastry, the comparison of two charts, Mercury is a vital factor because it helps us judge how two people will think together, or fail to do so.

Mercury is often underplayed in astrological writings yet it is a symbol of immense importance. Mercury represents the power of symbol making. It is connected to the mind, especially the logical and reasoning capabilities, and to all forms of communication. Likewise Mercury (along with Uranus) signifies the nervous system, because the nerves enable the organs to communicate among themselves.

The sign, house and aspect relationships of natal Mercury will contribute to what we think, talk and generally communicate about, our mental wavelength and have a lot to say about how we learn and what might impede, obstruct, support or accelerate this leaning process.

As Sue Tompkins points out hard aspects to an individuals Mercury may suggest that their opinions are likely to get tested and challenged by others, or that they expect them to be challenged, whereas soft aspects suggest the reverse. The person with soft aspects is less likely to feel threatened if disagreed with and so can often express themselves more easily. The challenge may come from within oneself or from outside, for therein lies the possibility of the mind and our ideas being stretched and broadened. As always the soft aspects, especially the trine can give rise to complacency, whereas the hard aspects offer the potential for growth.