Blues Harmony
The blues is the foundation of American music and one of the most versatile harmonic frameworks in existence. Its 12-bar form has been the basis for countless compositions across jazz, rock, R&B, country, and beyond.
The Basic 12-Bar Blues
The simplest form uses only three chords, all dominant 7ths:
I7 I7 I7 I7
| V7 | IV7 | I7 | V7 |In the key of Bb (the most common jazz blues key):
Bb7 Bb7 Bb7 Bb7
| F7 | Eb7 | Bb7 | F7 |The use of all dominant 7th chords (even on I and IV) is unique to blues harmony. In standard functional harmony, only the V chord is dominant.
Jazz Blues
Jazz musicians enrich the basic form with ii-V motion, chromatic passing chords, and substitutions:
Bb7 Eb7 Bb7 Bdim7
| Cm7 | F7 | Bb7 G7 | Cm7 F7 |Key additions: diminished passing chords (Bdim7 connecting Bb7 to Eb7), a ii-V turnaround in the last two bars (Cm7-F7), and a secondary dominant (G7 targeting Cm7).
Bird Blues (Parker Blues)
Charlie Parker's sophisticated version adds extensive ii-V motion:
Bbmaj7 Cm7 F7 Bbmaj7 Bbm7 Eb7
| Cm7 | F7 | Bbmaj7 | Cm7 F7 |This version treats the melody and harmony almost like a standard, with rapidly changing ii-V motion.
Minor Blues
The minor blues uses a minor i chord and typically draws from natural minor or Dorian:
Cm7 Cm7 Cm7 Cm7
| Dm7b5 | G7alt | Cm7 | G7alt|The ii-V in bars 9-10 (Dm7b5-G7alt) comes from harmonic minor and creates a strong resolution to the minor tonic.
Blues Tonality
Blues exists in a unique harmonic space where major and minor coexist. The "blue notes" (b3, b5, b7 over a major chord) create the characteristic ambiguity. This is why dominant 7th chords work on every degree — the b7 accommodates the blues scale's tensions. Understanding blues harmony is essential regardless of what genre you play.