In Western music there are twelve tonal centers (i.e. “keys”) and, therefore, twelve different notes:
A, B-flat, B, C, D-flat, D, E-flat, E, F, G-flat, G, A-flat
This is not a reflection of how nature actually operates. It was a very deliberate, man-made choice to equally divide an octave into twelve different parts (see: http://en.wikipedia.org/wiki/Well_temperament).
So why Twelve?
This is not entirely clear to me. But the number 12 has a rich history in society:
- 12 months in a year
- 12-hour clocks (60 seconds, 60 minutes, and a 24-hour day all divisible by 12)
- 12 signs in the Western and Chinese zodiac (In fact, the Chinese use a 12 year cycle for time-reckoning called Earthly Branches.)
- 12 astrological signs.
… Twelve is featured prominently in religion and myth:
- 12 Apostles
- 12 days of Christmas
- The biblical Jacob had 12 sons, who were the progenitors of the Twelve Tribes of Israel
- Eastern Orthodoxy observes 12 Great Feasts.
- Greek mythology contains the 12 labors of Hercules.
… Twelve leaves its mark all over society:
- 12 Function keys on standard keyboard
- There’s also 12 buttons on a standard telephone (0-9, #, *)
- We use the number twelve so often we have special words for it: Dozen. Noon.
Still, there is no apparent reason for choosing this one number over all others. The number spans time and cultures, yet notice that the number twelve always seems to be associated with earthly amounts. Look at the lists above. Even the religious figures are men and not deities. Zodiacs and astrology are systems to describe the fortunes of human beings. The number 12 seems to be a “safe” number in society. It’s what we use to designate the rational, the earthly, the countable.
So 13 would represent the “step beyond.” It’s the first number that can’t be reached, so to speak. Going back to the 12 Apostles, Jesus would be the 13th “transcendental” element. The song Twelve Days of Christmas came from the traditional practice of extending Yuletide celebrations over the twelve days from Christmas day to the eve of Epiphany. So the Epiphany is the 13th “transcendental” element. 12 Zodiac signs, plus the Sun. In Judaism, 13 signifies the age of maturity (bar mitzvah) for boys. The 13th floor on buildings supposedly doesn’t exist. And we all know to beware of Friday the 13th…
So the number 13, interestingly enough, has historically designated the spiritual, mystical, and transcendental.
Twelve represents rationality, and Thirteen represents mystery.