As their name suggests, half-step approach chords are chords which approach another chord either from a half-step above, or a half-step below. Typically, the approach chord will be the same type of chord as the chord it is approaching, for example, a minor seventh chord will approach a minor seventh chord, while a major seventh will approach a major seventh.
If we take a simple I – vi – ii – V progression in C major
we can create more harmonic and rhythmic interest with the use of half-step approach chords: from below,
or, through a combination of both.
Notice in these examples, that the half-step approach chord is always of a shorter duration than the chord it approaches, in other words it is rhythmically weaker. Approach chords do not always have to be used in this way, however, it is important to remember the non-diatonic nature of these chords: they decorate basic progressions but are subsidiary.
Occasionally, diatonic chords which are found a half-step from each other can be treated as approach chords. In the Red Hot Chili Pepper’s song Under the Bridge chord iii (G sharp minor) in E major can be heard as a lower half-step approach chord to chord IV (A).
In this context, the use of chord iii fulfils the role of a half-step approach chord, that is, it is subsidiary to the basic chord progression, I – V – vi – IV, which is repeated.