Numerology is any belief in the divine or mystical relationship between a number and one or more coinciding events. This is not to be confused with mathematics which deals with the more practical applications of numbers and concepts associated with numbers. On Discworld as on Roundworld, certain numbers take on significance greater than their actual numerical value. In many Christian cultures on Roundworld the numbers 3 & 7 are particularly significant; God created the world in 7 days. Jesus asked God 3 times if he could avoid crucifixion and was crucified at 3 in the afternoon. 13 is considered to be an unlucky number because that was the number at the table of Jesus' Last Supper and the number is often omitted in high rise buildings. In Chinese culture 8 is considered to be a lucky number while 4 is not. On Discworld the most prominent number is eight and it is never said because of its mystical status. In the novel, Going Postal (the first Pratchett novel with chapters) there is no chapter eight. At Unseen University, Rincewind's room was 7a which is the common substitution for the number 8.
Occurrance of the number eight:
- Eight is the number of magic.
- The eighth color of the rainbow is octarine and can only be seen by wizards and witches (by virtue of the octagons in their eyes), as well as other magical creatures. It is The Colour of Magic. In some rare instances, non-magical people can see it as an eye-watering blank space where a color should be.
- The Creator used eight spells to create the Discworld and these spells have been written down in the Octavo.
- The symbol of magic is the octogram, an eight-sided star.
- The eighth son of an eighth son always has magical abilities and has the right to study at Unseen University, an important component in Sourcery.
- The eighth son of an eighth son of an eighth son is a Sourcerer - a Source of Magic, the central theme in Sourcery.
- 7a is the number of Bel-Shamharoth. His temple has two to the power of three sides.
- There are eight orders of wizardry at the Unseen University.
- There are eight days in a Discworld week. Hence a Watchman being on-duty 24/8.
- There are eight Deadly Sins.
- There are eight Virtues.