In music, an approach chord (also chromatic approach chord and dominant approach chord) is a chord one half-step higher or lower than the goal, especially in the context of turnarounds and cycle-of-fourths progressions, for example the two bar 50s progression:Sokolow, Fred (2002). Jazzing It Up, p.11. .
|G / Em / |Am / D7 / || may be filled in with approach chords: |G F9 Em A♭m |Am D♯7 D7 G♭7 || F9 being the half-step to Em, Am being the half-step to Am, D7 being the half-step to D7, and G7 being the half-step to G. G being I, Em being vi, Am being ii, and D7 being V7 (see ii-V-I turnaround and circle progression).
An approach chord may also be the chord immediately preceding the target chord such as the subdominant (FMaj7) preceding the tonic (CMaj7) creating a strong cadence through the contrast of no more than two common tones:Felts, Randy (2002). Reharmonization Techniques, p.19. . FACE – CEGB.
Approach chords may thus be a semitone or a fifth or fourth from their target.Grove, Dick (1989). Arranging Concepts Complete: The Ultimate Arranging Course for Today's Music, p.139. .
Approach chords create the harmonic space of the modes in jazz rather than secondary dominants.Pease, Ted (2003). Jazz Composition: Theory and Practice, p.68. .
See also Passing chord Predominant chord Tritone substitution
References
Further reading R., Ken (2012). DOG EAR Tritone Substitution for Jazz Guitar, Amazon Digital Services, Inc., ASIN: B008FRWNIW