The Two Major Systems
Modern Western numerology is dominated by two main systems: the Pythagorean (also called Modern or Western) and the Chaldean (of Mesopotamian origin, considered the oldest).
The Pythagorean System
Attributed to the Greek philosopher Pythagoras, this system assigns values to letters sequentially and is the most taught in the contemporary West.
The Chaldean System
The Chaldean system is older and considers the number 9 sacred — therefore, it is not assigned to any letter. Values are based on the sound vibrations of letters, not their position in the alphabet.
Which System to Use?
Both systems have value and depth. The most important thing is consistency: choose one system, study it deeply, and apply it consistently before mixing approaches.