← Encyclopedia of Astrology · lesson 29/235
Mercury
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Mercury is the planet of the mind and of exchange: how a person thinks, learns, speaks and writes, and how they handle messages, numbers, contracts and trade. The tradition gives it scholars, clerks, merchants, the young, siblings and neighbours, and all short journeys. It is the go-between of the chart, taking on the colour of whatever it touches, which is why its sign and aspects say so much about the shape of someone's thinking.
Nature
Mercury is the convertible planet. Lilly calls it cold and dry in itself, but it is neither masculine nor feminine, benefic nor malefic: it becomes masculine with masculine planets and fortunate with fortunate ones, and joins the day sect when it rises before the Sun as a morning star and the night sect when it sets after it as an evening star. Its virtues are ingenuity, learning and craft; its faults, restlessness, overthinking and cunning.
Signs it rules and where it is strong or weak
Mercury rules two signs, Gemini and Virgo, and is unusual in also being exalted in one of its own homes, Virgo, traditionally at 15°. It is in detriment in Sagittarius and Pisces, and in its fall in Pisces too — the sign where the precise, sorting mind meets the boundless. Modern astrology keeps these rulerships.
Motion
Mercury is never more than about 28° from the Sun, so it is always in the Sun's sign or a neighbouring one. At full speed it moves nearly two degrees a day; it usually spends two to four weeks in a sign, and much longer when it turns back. It goes retrograde about three times a year for roughly three weeks each, slowing to a station at either end. In folk astrology Mercury retrograde has become a byword for misplaced messages and delays; the more measured reading is that it favours reviewing, revising and returning to things rather than launching them.
In a chart
Mercury's sign describes the style of the mind — quick or deliberate, practical or imaginative — and its house the subjects it naturally turns to. In the 3rd it inclines toward writing, teaching and local life; in the 6th toward craft and problem-solving at work; in the 9th toward study, languages and long-distance ideas. Mercury close to the Sun is common and, unless very close, is not read harshly by modern astrologers.
In transit
A transiting Mercury touches each natal planet several times a year, so its contacts are brief: a conversation, a message, a piece of news on the theme of the planet it meets. Its retrograde periods, when they fall on a natal planet, can bring the matter round two or three times before it settles.
In the tarot
The Golden Dawn's correspondences, which most English-language decks follow.
Major Arcana: The Magician
Decans it rules: Five of Pentacles (Taurus 0°–10°), Three of Cups (Cancer 10°–20°), Ten of Pentacles (Virgo 20°–30°), Eight of Wands (Sagittarius 0°–10°), Six of Swords (Aquarius 10°–20°)