numerology, use of numbers to interpret a person’s character or to divine the future. The theory behind numerology is based on the Pythagorean idea that all things can be expressed in numerical terms because they are ultimately reducible to numbers. Using a method analogous to that of the Greek and Hebrew alphabets (in which each letter also represented a number), modern numerology attaches a series of digits to an inquirer’s name and date of birth and from these purports to divine the person’s true nature and prospects.