As we've seen, harmonic progressions are essentially movements from the tonic (I) to the dominant (V) and back again. This exists not merely as a formal or theoretical construct, but also as an empircal or cultural one. The prevalence of this harmonic progression creates an expectation that dominant chords always lead to (or return to) the tonic chord.
Anything that is heard against that expectation is understood to be unusual, surprising, or otherwise noteworthy. A common maneuver is known as the "deceptive cadence." A deceptive cadence--like a plot twist in a movie--plays upon our expectations, but suddenly goes counter to them, creating surprise and interest. The "deception" is that as listeners, we're lead to believe the progression is moving in one direction (along the expected I-V-I axis), but is unexpectedly thwarted or detoured to an unexpected chord. The deceptive cadence always moves from V-vi (not I) as shown:
Note that the "expected" progression is I-IV-V-I, but instead an upward stepwise motion from V-vi creates an element of surprise.
In most instances, the motion from V-vi is almost immediately 'rectified,' with a strong assertion of the expected harmonic motion (for example, V-vi leads to ii-V-I, bringing about the 'real' conclusion to the progression.)
Music that avoids expected progressions (whether intentionally or not) are indexed, not to the established logic we've been discussing. That is to say, they "stick out like a sore thumb." Instances like this occur whenever someone or something appears to be radically out of place. A person showing up at a formal wedding in a gorilla suit would be understood to be radically out of place.
Consider the examples below, which are chord progressions that do not follow the established, expected approach to chord progression:
1. This progression (from I-IV-I) is known as a "Plagal Cadence," or also a "Church Cadence." (Think of the way hymns used to traditionally end--with a IV-I cadence on "A-men.") It is considered to be "not quite as strong" as a I-V-I motion.
Example: http://www.youtube.com/watch?v=zSm0M-BbVdY (beatles--hard day's night)
2. A motion from I-V-IV-I is definitely unusual. The study of this progression and its gradual ubiquity in the past 50 years could probably fill a book. It's almost unheard-of in traditional Music, but began to appear with frequency in American popular Music.
Consider these two examples below, which move from V-IV in an unexpected way:
http://www.youtube.com/watch?v=z9DVJE_bhVU (troggs--wild thing)
http://www.youtube.com/watch?v=GpGEeneO-t0 (shondells--crimson and clover)
3. A progression from I-vi-I is even less common than the previous two. Because the vi chord shares two pitches with the I, a motion from I-vi-I is often understood to be no progression at all--but rather an extension of the I chord (with an added or substituted note on vi).
- The motion from I-ii-I is again, another outlier. Any motion to the stronger IV or V chords is avoided.
The 'deceptive progression' as we discussed earlier, is an in-joke between the composer/performer and listener. The idea is that the listener is "set up" to be ready for a progression from V-I but instead hears V-vi, which can be poignant and surprising. The gag is almost immediately rectified by hearing the original progression, but now with a V-I movement. The surprising moment is carefully set up and resolved.
Progressions that do not employ this type of set-up/resolution may sound pleasing to some ears, but carry with them a different kind of message: a rejection of Music's tradition. Progressions that consciously avoid the Western tonal system of progression are worth exploring not because of their clever approach to the listener's expectations, but because of their rejection of tradition.
It is not surprising to learn that most of the standard "rock progressions" (some examples are given above) were developed during the "counterculture era" (1960-1980?) in American popular Music. The progressions reflect a societal rejection of the more careful and possibly "stale" chord progressions used by musicians in previous centuries, and instead portray a turbulent, youth-oriented society. Moreover, they are vehicles commonly heard in commercial products, so they must be understood in that context as well.
As such, progressions like the ones above are 'indexed' in our culture, to everything related to youth culture: voliatility, rebellion, depersonalization, hedonism, music marketing, advertising, and so on. Even a tiny musical signifier (like a guitar playing a I-V-IV-I progression) can be understood to be related to these ideals.