The twenty-third path joins Geburah, Severity, to Hod, Splendour, descending the left-hand Pillar of Severity from the sphere of judgement to the sphere of the intellect. It carries the letter Mem, whose name means "water", and which is one of the three mother letters of the Sefer Yetzirah, the primal trio Aleph, Mem and Shin, from which, in that text, the whole alphabet and the three basic divisions of the cosmos proceed.
The three mothers are assigned to the three elements of the ancient scheme: Aleph to air, Shin to fire, and Mem to water. Mem is thus not a planetary or zodiacal letter but an elemental one, carrying the formative power of water, the deep, the fluid and the maternal. Its position and its watery attribution come directly from the ancient Jewish source, where the three mother letters are the fundamental principles, the balance-beam holding fire and water in equilibrium with air between them.