The number 15, in the Qabalistic system of Liber 777, is the Mystic Number of Geburah, the fifth Sephirah. It is the triangular number of 5 (1+2+3+4+5=15), symbolizing the summation of the first five emanations and the rigorous, judgmental nature of the sphere of Mars.

Position on the Tree of Life

The number 15 corresponds directly to Geburah, the fifth Sephirah on the Pillar of Severity. Geburah represents divine judgment, strength, and the breaking of forms. As the mystic number of this sphere, 15 encapsulates the complete energetic expression of Geburah’s power—the total of the first five Sephiroth, from Keter through Geburah itself, indicating a culmination of force and limitation.

Astrological and planetary correspondence

While the number 15 is not a planet, its association with Geburah links it to Mars—the planet of war, discipline, and raw energy. In a secondary sense, 15 also appears in lunar symbolism as the day of the full moon, a time of maximum illumination and tension, echoing Geburah’s quality of decisive revelation. However, the primary astrological link remains Mars, whose red, aggressive nature aligns with the number’s triangular completion of the fifth sphere.

Historical context

The concept of mystic numbers in Qabalah derives from the Pythagorean tradition of triangular numbers, where each Sephirah’s mystic number is the sum of integers from 1 to the Sephirah’s own number. For Geburah (5), this sum is 15. In the Sepher Yetzirah, the number 15 is not directly named as a Sephirah, but the triangular pattern underlies the structure of the 32 Paths of Wisdom. Notably, 15 is also the number of the Path of Heh (the 15th path), but that path carries a different mystic number (120). The number 15 itself has a unique Hebrew spelling issue: the normal way to write 15 in Hebrew letters is Yod-Heh (10+5), which forms part of the Tetragrammaton (YHVH). To avoid writing a divine name in a profane context, Jewish tradition substitutes Tet-Vav (9+6) for 15. This substitution highlights the sacred potency of the number, linking it to the ineffable Name and reinforcing its association with Geburah’s role as a channel of divine severity. In later Hermetic Qabalah, as systematized by the Golden Dawn and Crowley’s 777, the mystic numbers serve as keys to the numerical correspondences of each Sephirah, with 15 standing for the rigorous, limiting aspect of the divine.

In Liber 777, the cell for Geburah under the column “Mystic Numbers of the Sephiroth” lists the number 15. This entry appears at scale step 5, confirming that the triangular sum of the fifth Sephirah is 15, a number that embodies the complete, forceful expression of severity and judgment on the Tree of Life.