Semi-sextile

A semi-sextile is the aspect of thirty degrees, half a sextile. Like the quincunx it corresponds to a classical relation of aversion between neighbouring signs, adjacent positions sharing no element, mode or polarity and therefore excluded from Ptolemy's four true aspects, and its use as an active minor aspect was taken up only later, in the broader harmonic tradition that grew out of Johannes Kepler's early seventeenth century reworking of aspect doctrine, though as with the quincunx the specific step of admitting the semi-sextile is more securely credited to the astrologers who extended Kepler's approach than to Kepler himself. It is also called the dodecile, from its status as one twelfth of the circle, a name that places it in the same family of repeated-division aspects as the octile and the finer divisions used by later harmonic astrologers.

Because thirty degrees is exactly the width of a zodiac sign, the aspect is generally read as one thing giving way immediately to the next, a mild and faintly uneasy adjacency rather than either harmony or open conflict. Some modern writers soften the ancient judgment further, treating the semi-sextile as weakly favourable, cooperation between neighbours rather than the mutual blindness Hellenistic doctrine originally assigned to it, which makes the semi-sextile one of the few minor aspects whose meaning has genuinely shifted rather than merely accumulated detail since it left the classical aversion doctrine behind.