Augmented Triad
Eb+ is an augmented chord built on Eb. The raised fifth creates an ethereal, unresolved quality. Augmented chords are less common in jazz standards but add distinctive colour, often used as passing chords or dominant substitutions (Levine, The Jazz Theory Book).
2 voicings · augmented
Augmented chords divide the octave into three equal parts (major thirds), giving them a symmetrical structure. This symmetry means there are only four unique augmented chords — every augmented chord is enharmonically equivalent to two others (Mulholland & Hojnacki, The Berklee Book of Jazz Harmony). In jazz, augmented chords often function as altered dominants or as part of Coltrane-style major third cycles.
The whole tone scale is the standard choice for augmented chords. The Lydian augmented scale (third mode of melodic minor) works for augmented major seventh chords (Levine, The Jazz Theory Book).
Augmented chords typically resolve up a half step. The #5 resolves up to become the root or third of the next chord.
Augmented approach
Eb+ approaching a chord a half step above
Coltrane changes
Augmented chords dividing the octave into major thirds
Eb+ contains Eb, major third, and augmented (raised) fifth. The symmetrical structure — three major thirds — gives it a floating, unresolved quality (Levine, The Jazz Theory Book).
The whole tone scale contains only whole steps, producing an ambiguous, floating quality that matches the augmented chord perfectly.
— Levine, The Jazz Theory Book, pp. 76-78