Mercury in astrology represents our logical mind, whereas the moon represents our emotional mind. Mercury is the part of us that is always taking information in so we can analyze it and make output out of it eventually. It is who we are when we are at work, making lists and running errands. The Mercury sign represents the way that someone goes about doing these things that are very closely connected to our material world and the traits connected with them. It also rules over communication and the way that we speak, write and communicate.
*PSA - you have a whole birth chart that is representative of your complete psychology and this is one small piece of it. If you would like a comprehensive reading, or to find out more about your Mercury sign, please e-mail me at firstname.lastname@example.org.
The twelve Mercury signs at their worst -
Aries: When Aries Mercury is showing its shadow, it will be hard to get a word in edge-wise. Especially when negatively aspected by Mars, angry and reactive speech will be a common theme. There is an instinctive belief that they are always right and so anyone who attempts to prove them wrong will be receiving an earful and even if they're wrong they will fight to the death about it.
Taurus: When Taurus Mercury is low-functioning, they will be very reticent to a change in their systems of thought and speech, even if that is what is called for. Sometimes, the virtue is not in communicating the way that you want to communicate something, but how people need to receive the message so they can assimilate it properly. Taurus Mercury at its worst will refuse to acknowledge that and not understand why there are miscommunications.
Gemini: When Gemini Mercury is showing its shadow, this can look very much like manic thought and speech. This can appear like talking so fast that no one can keep up and the line of thought not really making sense and jumping around erratically. Since Mercury rules over our work nature, this can appear like someone who takes on way too many projects at a given time and then doesn't show up fully in the course of each project.
Cancer: When Cancer Mercury is low-functioning, their form of speech and thought is so subjective and not consistent on even an hourly basis. Cancer is ruled by the moon and so wherever Cancer is placed can very much wax and wane and change, just like the moon's phases. A Cancer Mercury that is struggling will not even realize that in the grand scheme of things, everything will be okay and there is an inability to see how changeable things are and ride the wave.
Leo: When Leo Mercury is riding the struggle bus, they don't really want to hear anyone else's perspective. Their mindset is that they're the boss, so they won't even validate what anyone else has to say about anything. They can also really over-promise and under-deliver, relying on the charm of their speech to get them by.
Virgo: When Virgo Mercury is at its worst (I know from experience), they literally are afraid to leave the office or trust any form of work in the hands of anyone else for the fear that someone else will gloss over a detail or not get things done in the way that they would. This placement is known for its perfectionism, so the output of others as well as the output of the Self can be criticized all to death.
Libra: When Libra Mercury is at low-funtioning, they can be a different sort of perfectionist - one that wants balance in every part of their life. They can see all sides of any given scenario which makes them incredibly indecisive, which is not good when most jobs require on-the-spot decisive action. They can also have the tendency to not want to disappoint anyone so they'll tell white lies or big grandiose ones, not known for being the most honest of folk.
Scorpio: When Scorpio Mercury is struggling, it takes the same intensity that a homicide detective takes into their toughest case into their every day life, surrounding work and communication. An inability to drop things or to forgive shows up with this. Sometimes, this placement at its worst can look like someone who's not afraid to throw a low blow.
Sagittarius: When Sagittarius Mercury is at its worst, it could be quite forgetful. Glossing over the details and also taking gigantic risks can be a bit of a disastrous combination, especially when it comes to spending money. This placement could also get carried away with positivity to the point where there becomes a disconnect from reality.
Capricorn: When Capricorn Mercury is exhibiting its shadow side, it won't take any risks. It doesn't want to deviate from any sort of plan in thought or speech based out of an implicit fear that something may then go wrong. They feel like they need to follow step-by-step methods and sometimes life requires people to think on their feet. Additionally, this native can be limited in their speech, communication and what actually gets shared with even their loved ones.
Aquarius: When Aquarius Mercury is displaying its low qualities, it can know and see too much in a very objective and logical way. As they say, ignorance is bliss and knowing too much can really weigh heavily on a person. This kind of thing can actually lead an Aquarius Mercury into a depression where they don't even feel like they can innovate, which is one of their best qualities.
Pisces: When Pisces Mercury is at its worst, it can move through life in a fog of miscommunications and missed appointments and deadlines. The ability to get lost in their own creative consciousness is very much prevalent with this Mercury sign in its worst manifestation to the point that they drown out the rest of the world and become consumed with their own creative mind.