Understanding Diatonic vs. Non-Diatonic Chords in Nashville Number System

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The Nashville Number System (NNS) is a method used by musicians to quickly communicate chord progressions using numbers instead of traditional chord names. It simplifies transposing and playing music across different keys. A fundamental aspect of understanding NNS involves distinguishing between diatonic and non-diatonic chords.

What Are Diatonic Chords?

Diatonic chords are built from the notes within a specific key or scale. They follow the natural harmony of that key, making them predictable and easy to identify. In the Nashville Number System, diatonic chords are represented by numbers that correspond to the scale degrees.

Understanding the Nashville Number System for Diatonic Chords

In a major key, the diatonic chords are typically:

  • 1 (I) – Major
  • 2 (ii) – Minor
  • 3 (iii) – Minor
  • 4 (IV) – Major
  • 5 (V) – Major
  • 6 (vi) – Minor
  • 7 (vii°) – Diminished

These numbers are used to denote chords that naturally occur within the key. For example, in the key of C major, the diatonic chords are:

  • C (1/I) – Major
  • D minor (2/ii) – Minor
  • E minor (3/iii) – Minor
  • F (4/IV) – Major
  • G (5/V) – Major
  • A minor (6/vi) – Minor
  • B diminished (7/vii°) – Diminished

What Are Non-Diatonic Chords?

Non-diatonic chords are chords that do not belong to the key’s scale. They are borrowed from other keys or modes, or created through chromaticism. These chords add color, tension, and interest to a progression, often leading to a resolution back to diatonic chords.

Using Non-Diatonic Chords in Nashville Number System

In the Nashville Number System, non-diatonic chords are indicated by adding symbols or accidentals. Common ways to denote them include:

  • Adding a slash (/) to show a chord borrowed from another key or mode
  • Using a flat (b) or sharp (#) to indicate chromatic alterations
  • Specifying a different root note

For example, in a progression in C major, a non-diatonic chord like a G7 (dominant seventh) borrowed from the G mixolydian mode might be notated as V7 or sometimes with additional symbols to indicate its borrowed nature.

Examples of Diatonic and Non-Diatonic Chords

Consider a common progression in C major:

  • C (I) – Diatonic
  • F (IV) – Diatonic
  • G (V) – Diatonic
  • E7 – Non-diatonic (borrowed from the harmonic minor or other modes)

Using non-diatonic chords like E7 creates tension that resolves nicely back to the tonic (C), adding emotional depth to the progression.

Conclusion

Understanding the difference between diatonic and non-diatonic chords is essential for mastering the Nashville Number System. It allows musicians to create more dynamic and expressive progressions, whether staying within the key or intentionally adding outside elements for color and tension.