Mercury is a small, fast planet that travels the zodiac in about a year, like the Sun, which is why the only conjunction possible between the Sun and Mercury is a major aspect. Mercury is always in the same sign as the Sun or just beside it, for example, a person of the sign of Aries will have Mercury in Pisces, Aries, or Taurus, there is no other possibility.
Mercury governs intellect, communication, information, and our way of thinking and expressing our ideas. He, therefore, often plays an intermediary role. It is also the planet of travel, mobility, exchanges, meetings, and commerce. The transits of Mercury, even if they are fast, have daily repercussions and complete other more critical transits with the slow planets. Its effects last only a few weeks, except when it's in retrograde. It can also trigger an event or climate announced by the transit of a slow planet.
Its passing as a sign gives color to the exchanges between people for about three weeks, and its interpretation can constitute valuable information for all those who depend on a clientele, the public, commerce, or the small business or publishing sector.
*The Retrograde: Mercury goes into retrograde for 24 days every 88 days.
It is one of the most perceptible transits, both at the general and personal levels. All mercurial functions are slowed down, blocked or reversed: delays, breakdowns, blockages, administrative problems, technical problems, distractions, oversights. Communication between people is difficult.