Mercury in Cancer.
A thing to remember here is that these posts are strictly meant for the particular planet position. Like, today we are looking at Mercury in Cancer, so the description given here may change for you if your Mercury is although in the sign of Cancer but with conjunction with or aspected by other planets.
So, lets see what Mercury can do in Cancer without any conjunction or aspect from any other planet. 1st lets see what these 2 things represent --
Mercury represents communication skills, marketing, calculative ability, younger siblings, hobbies, skills with hands, intelligence, quick decision making, logical thinking, youthfulness etc.
Cancer is 4th sign of Zodiac Belt, hence it represents the things represented by 4th house like Mother, Mother's care, Emotions and Nourishment etc. Cancer is consisted of 2 and half Nakshatras namely Punarvasu, Pushyami and Ashlesha. Cancer's lord is Moon.
So, now Mercury is coming into sign of Cancer, which represents Emotions. Mercury is in enemy sign here as Cancer is ruled by Moon. This shows that person can be highly emotional when he communicates, either in oral or in writing. They can write very emotional stories which can make people cry. They will also love to act in emotional roles. But where it hurts most is Mercury is intellect and Cancer is emotions. So, person's intellect suffers due to emotions. It means that they can leave a great business deal due to some emotional reason. If their friends request them to do something, then they may do it even at the cost of hurting self. So, it makes them a kind of emotional fool in early life. But this is what they are supposed to learn and improve.
Now, the question comes about the level of emotional communications and decisions a person may take? So, it again would depend on the Nakshatra Mercury is sitting in. If Mercury is in Punarvasu Nakshatra, then emotions will be directed by the condition of Jupiter in horoscope as Punarvasu's lord is Jupiter. If Mercury is in Pushyami Nakshatra, then emotions will be directed by the condition of Saturn in horoscope as Pushyami's lord is Saturn. Again, If Mercury is in Ashlesha Nakshatra, then it is little better as it is Mercury's own Nakshatra..
Also, as Cancer is ruled by Moon, we need to look at Moon's position. Moon's position will actually determine that how Mercury is going to behave in Cancer. Again, horoscope should be judged in its totality.