Sun conjunct Mercury in a birthchart denotes a quick thinker and a good communicator. This person is fast on his feet when cornered with questions, or sometimes even when physically cornered. He or she may be evasive, or hard to pin down. They acquire information, and enjoy passing it on. Words are both a tool and a weapon for them. They may be slick in their use of words, or even untruthful, but you will be fascinated by what they say anyway.
Some people with this aspect are interested in learning but on their own terms. They value education but get bored easily. They may be good teachers in subjects that are interesting to them. They are often funny and charming, and children usually enjoy their company. They are chatty with neighbors, friends, and relatives, perhaps to the point of being gossipy.
These people are changeable, and not always reliable, but are almost always fun to be around. They are entertaining, and are good mimics. Comedy comes naturally to them.
Sun Conjunct Mercury people cannot sit still, and may often be on the move. Traveling with them is never dull. Even commuting turns into a small adventure with them.