Digital Sound & Music: Concepts, Applications, & Science, Chapter 3, last updated 6/25/2013
root note is either C or the B below C, making it easier for your hand to move from one note to
the next. Thus, chord I can be played as C, E, G; chord IV as C, F, A
inversion); and chord
V as B, D, G
inversion), as shown in Figure 3.37.
Figure 3.37 “Twinkle, Twinkle Little Star” with chords in bass clef
A simple way of looking at chord progressions is based on tonality – a system for
defining the relationships of chords based on the tonic note for a given key. Recall that the tonic
note is the note that begins the scale for a key. In fact, the key’s name is derived from the tonic
note. In the key of C, the tonic note is C. Triad I is the tonic triad because it begins on the tonic
note. You can think of this as the home chord, the chord where a song begins and to which it
wants to return. Triad V is called the dominant chord. It has this name because chord
progressions in a sense pull toward the dominant chord, but then tend to return to the home
chord, chord I. Returning to chord I gives a sense of completion in a chord progression, called a
cadence. The progression from I to V and back to I again is called a perfect cadence because it
is the clearest example of tension and release in a chord progression. It is the most commonly
used chord progression in modern popular music, and probably in Western music as a whole.
Another frequently used progression moves from I to IV and back to I. IV is the
subdominant chord, named because it serves as a counterbalance to the dominant. The I IV I
progression is called the plagal cadence. Churchgoers may recognize it as the sound of the
closing “amen” to a hymn. Together, the tonic, subdominant, and dominant chords and their
cadences serve as foundational chord progressions. You can see this in “Twinkle, Twinkle Little
Star,” a tune for which Wolfgang Amadeus Mozart wrote twelve variations.
The perfect and plagal cadences are commonly used chord progressions, but they’re only
the tip of the iceberg of possibilities. “Over the Rainbow” from The Wizard of Oz, with music
written by Harold Arlen, is an example of how a small variation from the chord progression of
“Twinkle, Twinkle Little Star” can yield beautiful results. If you speed up the tempo of “Over
the Rainbow”, you can play it with the same chords as are used for “Twinkle, Twinkle Little
Star,” as shown in Figure 3.38. The only one that sounds a bit “off” is the first IV.