Referring back to the illustration of typical large scale harmonic motion that I provided in the chord progressions lesson is helpful when studying this concept of connecting progressions. The ultimate destination in this illustration is the final tonic chord. However, any chord along the way can be thought of as a temporary target point. When using this thought process, the composer or performer can think of the target chord as a temporary key center. Although the large scale key signature has not changed, it is temporarily displaced by a progression that is leading to the target chord.
Another technique, beside five-one chromatic progressions, is the use of diminished chords. A diminished triad or seventh chord who's root is half a step below the target chord's root can be used as another mode of travel. This technique is successful even when approaching a diminished target chord.
This Learning Music With Ray video discusses the chord progressions used to connect one structural chord to another. While playing chord progressions, it is common practice to think of the chord we are traveling to as a target or temporary key. In this video, I discuss chromatic chord progressions that can be used to travel to temporary key centers or target chords. I refer back to the illustration of large scale harmonic motion and point out ways that target chords could be approached. I also demonstrate these connecting chord progressions on the piano.