Mercury is the planet of communication. If you don’t believe me just try having a brief conversation with a Gemini. It makes no difference with Mercury. Writing or speaking this planet has got to move information.
Mercury Aspecting the Sun: The only possible major aspect is the conjunction, since Mercury never gets more than 28 degrees from the Sun. This aspect has a reputation for giving a little extra mental stability. It can also add to the communications ability. Remember, any planet in conjunction with the Sun will give the person traits of the sign (or signs) that the planet rules. In this case, that would be Gemini and Virgo, two signs that are good dealing with information.
Mercury Aspecting the Moon: The stressful aspects (the square and opposition) increase the desire to take short cuts in all things. Mercury rules the “conscious mind” and the Moon the “subconscious”. Stressful aspects, particularly the opposition intensify the normal tension between these two. Your “gut instincts” are constantly telling you to do something other than the conclusions you reach by logic. Additionally, there is a danger that you will either not say what you feel or that you will ONLY say what you feel, not thinking things through before you speak. As always though, the stressful aspects should be seen as obstacles to be overcome. Once they are worked on, stress aspects can usually be turned around and become a source of strength. In this case, that would mean strong, instinctive communications ability. The harmonious aspects smooth the thought and communications process and incline the person who has them towards work requiring lots of communicating.
Mercury Aspecting the Ascendant: The conjunction can make you act like a Gemini or Virgo, always concerned with communication and details. Both the conjunction and opposition can give good communication ability. Adolph Hitler had the opposition and it helped him seduce a nation. The opposition also can give a talkative partner. Squares are always obstacles to be overcome. In this case, it’s with communications. Mercury square the Ascendant increases the chances that you will be misunderstood and that you will misunderstand others. This will be especially true for partners. The sextile and trine make communications seem to flow. Sometimes it seems as if you can talk about anything at all and sound as if you are an expert in the field. This is because you have an attraction for random bits of information, picking them up wherever you go. You may, on occasion, be mistaken for a walking encyclopedia.
Mercury Aspecting the Mid-Heaven: is common in the horoscopes of writers, Steven King being a good example. Other Mercury professions are also common, such as sales or anything involving public speaking. Mercury also rules transportation so travel agent, flight attendant, pilot, and even truck and cab drivers are included here. At least one parent was probably talkative or moved around a lot.