Mercury in Capricorn

Tropical is a term used by Ptolemy (Ashmand's 1822 translation) for a sign where the Sun turns, and he gives a long list of what such signs do to the mind. It runs from public ambition and religious study to acute, inventive and speculative thinking, with astrology and divination mentioned in passing. Mercury is one of his two keys to that list, so Capricorn is a case where the rule applies directly.

Capricorn belongs to Saturn in the older scheme. Lilly 1659 describes Mercury as cold and dry by nature and Capricorn as cold and dry too, which puts the planet in a sign that matches its temperature. He gives it degrees 7 to 12 as terms.

Adams 1928 reads the sign as severe and unrelieved, and Alan Leo 1899 as exact and methodical. Modern readings of this Mercury generally follow Leo toward method and planning. Which book one prefers changes the picture a good deal.