Sun and Mercury conjunction in a birth chart can give a person extra thinking abilities. They can be fast learners and a have sharp minds. They are also good at communication and expressing their thoughts into words. They have a way with explaining things with their words in ways other may not be able to as easily. Sometimes though this can make a person talk in a fast manner trying to convey all going on in their head. These people have something to say and most of time needs to be heard and received by others. If Sun or Mercury are either conjunct in the sign of Virgo or Gemini in a persons chart this would be even more so given that these signs are ruled by Mercury naturally. It can be helpful if these people to write sometimes, as this helps them focus and channel their words better.