The seventeenth path joins Binah, Understanding, to Tiphareth, Beauty, descending from the supernal mother to the harmonising centre. It carries the letter Zayin, whose name means "sword" or "weapon", and whose form suggests a blade, an image of discrimination, of cutting and dividing, and so of the choices and distinctions the mind must make.
In the Sefer Yetzirah Zayin is one of the twelve simple letters assigned to the twelve zodiac signs, and it is given to Gemini, the twins, the mutable air sign of duality, communication and the pairing of opposites. The attribution of the letter to Gemini is part of the ancient Jewish scheme in which the twelve single letters correspond to the signs of the zodiac and the months of the year; the sign of the twins, with its theme of two joined and two divided, suits a letter whose sword both separates and, in the choosing, unites.