Approach chord

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:

may be filled in with approach chords:

F9 being the half-step to Em, A♭m being the half-step to Am, D♯7 being the half-step to D7, and G♭7 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:FACE – CEGB.

Approach chords may thus be a semitone or a fifth or fourth from their target.

Approach chords create the harmonic space of the modes in jazz rather than secondary dominants.

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Wikipedia