A "Substitution" is when a chord replaces or is used in addition to an existing chord. Chords can have an active or passive quality to them. Active chords tend to be restless and want to move on to other chords. Passive chords tend to offer a feeling of rest and resolution. This cycle of active and passive chords are what gives chord progressions their feeling of movement.

A core set of basic chords that ALL Ukulele players should know in common keys.

These chords are movable, three note chord forms. The triad is the chord