When studying the interactions between individuals in a relationship, looking to Mercury cross-aspects and interactions can be revealing and insightful. First and foremost, determine the element of each person's Mercury.

Mercury in Fire people (that is, those with Mercury in Aries, Leo, or Sagittarius) express themselves with vigor. They are most comfortable thinking and talking about personal desires and visions than practical affairs, and are not particularly concerned with other people's perspectives. They generally express themselves with confidence, energy, and enthusiasm. They'll defend their ideas with passion. Their plans may not be practical or particularly sensible, but they are optimistic.

Mercury in Earth people (that is, those with Mercury in Taurus, Virgo, or Capricorn) are most concerned about handling practical, day-to-day problems. They take on a logical approach to problems, and stick close to the physical plane in their thoughts and concerns. These natives are results-oriented.

Mercury in Air people (that is, those with Mercury in Gemini, Libra, or Aquarius) generally come across as intellectual sorts. They easily and happily think in abstract terms. These natives can be quite argumentative, but unlike those with Mercury in Fire, their emotions are not necessarily behind these arguments. They simply look for intellectual stimulation. They are adept at taking overviews of situations, and are particularly concerned about how everyone, and everything, relates to each other. They have many interests, can be objective and detached in their thought and communication processes, and may be inclined to think more than act.

Mercury in Water people (that is, those with Mercury in Cancer, Scorpio, or Pisces) are the least argumentative of the bunch. These natives concentrate on feelings and relationships, and avoid communicating in abstract terms. They take things more personally. They are impressionable and sensitive to others. Many nurture others through their communications. Their focus is more on intangibles, so they can appear irrational or undisciplined to some. These people just "know" things and are less inclined to analyze, preferring to feel things out.