2. Although the famous and perhaps first Kabalistic book, The Sefer Yetzirah, clearly says there are ten, not nine, not eleven Sephiroth, many modern Kabalists consider Da'ath to be the eleventh Sephirah. Even so, many consider Da'ath to be a "pseudo-Sephirah," "the invisible Sephirah," or even "the Sephirah that is not a Sephirah." Some picture this in line with the second and their Sephiroth, however it is more traditionally just below it, right on the Veil of the Abyss that demarcates the line between human (below) and more than human (above). Being able to move from one part of the Tree of Life to the other requires Knowledge, and that is the meaning of the Hebrew word Da'ath.
Eleven is considered a "master number" in Western numerology. It is composed of a mix of five (the pentagram, which is representative of the elements shown at its points) and six (the hexagram, which is representative of the planets shown at its points), combining practical and spiritual magick. Thus, eleven is the universal number of magick.