Chords: Chord Structure: The Number System

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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
piano-ology-chords-chord-structure-number-system-one-octave-notation
piano-ology-chords-chord-structure-number-system-one-octave-keyboard
  • 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)…

piano-ology-chords-chord-structure-example-c-major-triad-notation
piano-ology-chords-chord-structure-example-c-major-triad-keyboard


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…

piano-ology-chords-chord-structure-number-system-two-octaves-notation
piano-ology-chords-chord-structure-number-system-two-octaves-keyboard

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

piano-ology-chords-chord-structure-example-c-major-7-add9-notation
piano-ology-chords-chord-structure-example-c-major-7-add9-keyboard

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)

piano-ology-chords-chord-structure-example-c-minor-7-notation
piano-ology-chords-chord-structure-example-c-minor-7-keyboard

Using the number system above, you can describe the structure of any chord type. Don’t worry about learning them all at this point. You will have lots more exposure to the naming conventions as needed in future lessons.

learn more… Intervals You Gotta Know