Mercury, so often overlooked in astrology as it is so close to the Sun and often in the same sign, yet symbolises an essential part of our make-up. Mercury signifies the nervous system within our bodies, that which sends messages from one part to another, pleasure and warning signals, conveying the knowledge about whether a part of our experience is worth exploring further or running away from with haste. This is a Gemini function. Mercury also signifies the intestines, where the food we take in is digested, analysed and reconstituted in a way that our bodies finds serviceable - a Virgo function. When Mercury in the birth chart is in one of these signs (which it rules), the aspects of personality which these functions represent are often manifest in a positive way. A particularly important function of Mercury is that shown by Hermes (the Greek version of Mercury), who was the only god who could move from the visible world to the under-world. In our daily lives this signifies the interaction between the conscious and unconscious parts of ourselves. When Mercury is functioning well in the horoscope it can indicate that we live from self-knowledge. We can live socially acceptable lives, not out of a superficial concern for morally upright behaviour, but rather from a deeper place within us that is well aware of instincts that rebel against the acceptable. When we accept the darker side of our own natures, we live in the world and act with love, not from mere morality.
But Mercury itself also has a darker side. The nervous system can give us false messages. In Greek myth Hermes was a notorious liar as well as a guide of souls! A difficult relationship between Mercury and other planets in the horoscope may show an inclination to use knowledge to trick other people in order to gain something we perceive to be advantageous. Even knowledge of the unconscious, which can be an immense force for good, can be used to think of ourselves as better than those who live what we may perceive to be superficial lives. Superficial contact with the unconscious rather than deep exploration can lead to obsession about other people's lives to the extent we will not rest until we have the information we want. This can be exhausting for us and invasive for others.