We all have trouble sometimes communicating properly with our partners. Mercury is the ruler of communications and shows our communicating style, so if you can adjust to their own style when trying to get through to them, you might be more successful. Give it a try!
Their Mercury sign:
If you're talking to an ARIES Mercury: No long speeches or conversations! You'll lose them after 10 seconds. They've got a super short attention span, so get to your point quickly without much to preface it. Be direct, to-the-point, and don't add in unnecessary details.
If you're talking to a TAURUS Mercury: If you can find a way to incorporate the senses into what you're saying (using a graph or pie chart, pictures, diagrams) or give tangible examples of what you're trying to convey, they'll have an easier time getting it. If not, be ready to explain things in detail and don't fudge anything.
If you're talking to a GEMINI Mercury: Be logical and rational when you speak to them. Don't talk about anything important at the same time you're crying or screaming, because they'll dismiss anything you say. They listen to people they think are "smart," so feel free to use big words.
If you're talking to a CANCER Mercury: They remember more when the mood is set. Talk to them when you're emotional or the situation is emotional. They respond to emotional communications and kind of absorb the mood, thereby absorbing the information. But don't yell at them - they get wounded very easily through words.
If you're talking to a LEO Mercury: Think of yourself as a salesman and you're pitching your thoughts to them. Be warm in your communications and act like it's all for their own good. Sprinkle in a little praise and you'll really have them. Criticize and they'll scamper away. Don't dwell on the details too much either.
If you're talking to a VIRGO Mercury: Here, dwell on the details all you want! They can process every little detail you throw at them. They have a harder time processing the big picture stuff though, so instead of one big talk, break it up into several small ones. Be logical and no-frills.
If you're talking to a LIBRA Mercury: Now these people, you can compromise with. They *love* a good compromise. No yelling either - if you sound remotely unpleasant, they're miffed and walking away. If you want to drive home a point, be non-threatening, maybe even sideways. And if you're tired of them always taking the other side, just play reverse psychology.
If you're talking to a SCORPIO Mercury: They love digging deep into subjects, so let them. Give just a little and let them ask all the questions they want. Don't make things too personal with them, because then that Scorpio stinger comes out. And *actually* listen to them - no pretending!
If you're talking to a SAGITTARIUS Mercury: Don't go to them with the little details - they're not so great with that. They're better at the big picture, so start there. Don't mind their candid nature, they just don't think too much before they speak, so take a deep breath before yelling. Actually, make them laugh before getting into anything because it'll put them in a better mood.
If you're talking to a CAPRICORN Mercury: Try not to be too emotional or give them too much to think about. Little bits of information at a time is best. And don't beat around the bush, get right to it and don't waste any time.
If you're talking to an AQUARIUS Mercury: They may seem like they love to fight, but it's more like they love to make you see other ways of thinking, especially when they believe you're being close-minded, so make sure to approach them with an open stance on matters.
If you're talking to a PISCES Mercury: Listening isn't a problem for them, but telling you what they think probably is. It isn't that they don't think, it's that they think through their emotions, and they're afraid of bruising anyone. Be gentle and don't try to bully them into talking, and maybe try to converse in the abstract, or get them to communicate through some form of creative expression.
Suggested Reading: The Natal Mercury page for general interpretations for Mercury signs