# Chords: Chord Structure: The Number System

The commonly-used convention for describing Chord Structure is a number system that uses the major scale as the point of reference.

The system works as follows:

• Numbers are assigned to each note in the major scale in ascending order.
• In the key of C: C=1, D=2, E=3, F=4, G=5, A=6, B=7
• The number “1” always represents the root of the chord — always!
• The other numbers correspond to notes in the major scale beginning on the root note.

Example: C Major Triad (chord structure = 1-3-5)…

In addition, chords that include “9ths”, “11ths”, and “13ths” are possible. Let’s add those to the mix in the key of C: D=9, F=11, and A=13…

Example: C Major 9th (structure = 1-3-5-7-9)…

Furthermore, chord tones are not limited to just the natural notes in a major scale. To include all possible notes, any of the numbers can be modified by sharps or flats.

Example: C Minor 7th (chord structure = 1-b3-5-b7)

Using the number system above, you can describe the structure of any chord type.