The inner planet Mercury symbolizes the conscious mind: all the faculties that are connected to the mind and arise out of the mind. We make sense of our world by taking the inputs from our senses and interpreting them a certain way.

This interpretation is our perception: the way we choose to interpret is the way we perceive the world. We all know that the same environmental factors with the same set of sensate stimuli will be interpreted differently with different people. While one person might perceive a genuine compliment, another person might perceive forced politeness. A statement perceived as sarcasm by someone might be taken as straight talk by another.
What the mind processes and perceives is communicated to others. Communication is a Mercurial function. The manner in which you communicate orally or in writing is determined by Mercury’s placement, which informs what tone you adopt and how your communication comes across to others.
Basic sensate stimuli evolve into higher order functions such as reading and making sense of words, watching and making sense of images, listening and making sense of what we hear. All of these higher order functions are the ways in which we learn as we accumulate increasing amounts of data.
Learning, and inter-connecting the various things we have learned over time helps us convert data to knowledge. And we can transmit what we know by writing or speaking about it.
Aside from perceiving and communication, thinking in and of itself is also Mercury’s business, since it occurs in the mind. The thinking can be a side-effect or after-effect of sensate stimuli — “wow, this juice tastes really good.” Or, the thinking can be triggered by other factors in the environment– “it is so cloudy, is it going to rain?”, or it can arise independently of any immediate external trigger– “wonder who’s going to win the game tomorrow”.
So thoughts, and ideas are Mercury’s domain. And so are speed and dexterity, to do with how rapidly these thoughts and ideas flit through the mind, how adroitly they are processed, and how quickly they are acted upon.
There are other meanings for the Mercury symbol drawn from various sources including mythology.
Mercury is the connector or broker, serving as the bridge between two or individuals, groups, or even ideas. It is the guide, the one that shows the way. (Think tour guides, or teachers.)
Mercury is the prankster, carrying within it a childlike quality suffused with mischief and wonder that can be a refreshing antidote to cynicism.
Keywords: Mind, Communication, Speaking, Writing, Reading, Watching, Listening, Learning, Knowledge, Thinking, Ideas, Dexterity, Broker, Mediator, Guide, Prankster, Trickster, Mischief, Youth