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 like this:

  • 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-1-octave-notation

piano-ology-chords-chord-structure-number-system-1-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-2-octaves-notation

piano-ology-chords-chord-structure-number-system-2-octaves-keyboard

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

piano-ology-chords-chord-structure-example-cmaj9-notation

piano-ology-chords-chord-structure-example-cmaj9-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-cm7-notation

piano-ology-chords-chord-structure-example-cm7-keyboard

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

About Frank J Peter

A uniquely burdened and blessed citizen of the world thinking and acting out loud!
This entry was posted in Chords, Music Theory and tagged . Bookmark the permalink.

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