In Astrology, the Sun represents our core being, while Mercury represents our communication style.
Sun conjunct, sextile, or trine Mercury
Mercury synastry aspects are undervalued in astrology, in my opinion. What kind of relationship can you have, if you can’t even talk to one another. Sun-Mercury aspects in synastry are thus very important. In harmonious aspect, Sun-Mercury aspects stimulate communication between partners. They like to speak to one another, and have similar intellectual interests. This isn’t an indicator of a wild, passionate romance, but having good communication with your mate is one of the most important aspects of a successful relationships.
Sun opposite Mercury
This aspect indicates a difference of opinions and perspectives on intellectual issues. This aspect indicates lively mental exchanges and interesting conversations.
Sun square Mercury
With this aspect, there comes a tendency to criticize each other’s viewpoints. The Sun person may feel sensitive to Mercury’s criticism, and Mercury may find the Sun person defensive. It’s hard to “get” what the other is saying with this aspect. With a little patience and understanding, you can learn a lot from one another.