Voice leading refers to the smooth transition from one chord to the next in a chord progression. The basic idea is to move each voice (note) in a chord as little as possible in a melodic and interesting way.
The rules of voice leading are:
- Keep common tones in the same voice
- Move uncommon tones as little as possible
Any Chord can be preceded by its V7, which is typically called a perfect cadence.
Any V7 can be preceded by the IV (this is common in classical music)
The IV can be substituted by the IIm7 since they both have the same tonal function.
Any chord can be substituted by another chord with the same tonal function in order to create a stronger root movement of fourths. Below, the I chord (C major) is substituted by the vim7 (A min7)
Below, the I chord (C major) has been substituted by the IIIm7.
Any chord can be preceded by its V7 (when the target chord is a diatonic chord). The V7 (dominant chord) is called a “Secondary Dominant”.
Below, the V7 of the primary dominant G7 which is D7 (V7/V), is shown highlighted in red.
The V7 is commonly preceded by the IIm7, even when it breaks the target chord (G7) of a secondary dominant (D7). This IIm7 is called the “relative IIm7” because it’s the relative minor chord of the preceding secondary dominant.
