Rock musicians just can’t resist a plagal progression, and I think I know why.
Perhaps it’s part of their nonconformist nature. Classical/concert and rock/pop music share more in common than most people from either side would be willing to admit, and whether it is done consciously or subconsciously, rock music contains several of concert music’s established traditions regarding melody, rhythm, and other musical elements. There are obvious differences, particularly regarding timbre and orchestration, but one of the more subtle points of departure between the genres is their approach to the chord built on the fourth scale degree of the given key (consisting of scale degrees 4, 6, and 1), which will be referred to hence forth as a IV chord (traditionally, diatonic triads are referred to by Roman Numerals, using upper case for major chords and lower case for minor).
In classical music, the IV chord is, outside of the tonic (I) chord, the most versatile diatonic harmony, but it is most frequently used as a predominant chord. A predominant chord, as its name would imply, introduces dominant (built on scale degree 5; a V chord) harmony. However, the IV chord is used less commonly as a predominant harmony than a chord built on scale degree 2 (ii chord: it consists of scale degrees 2, 4, and 6, but when the chord seventh [scale degree 1] is added, it is virtually interchangeable with a IV chord).
The plagal progression is used in classical music, but it is a relatively infrequent occurrence. A plagal progression is defined as a IV moving directly to I rather than V. The “A-men” on hymns is the most obvious example, though the Hallelujah Chorus from Handel’s Messiah, which is chock-full of the IV-I progression, is probably the most well known example from concert music. Examples such as this tend to be the exception, though, and the plagal cadence is used so irregularly that it is considered to be the weakest of all tonal progressions in classical music, if it is even considered to be a cadence at all.
Granted, this is a very subtle (lame?) way of sticking it to the man, but people who write rock/pop music use the IV chord far more frequently than those who write classical/concert music. They are used so frequently that their sound has become identifiable to even an untrained ear. If you’re not sure if you’ve ever heard a IV chord before, here’s a simple test: have you ever heard a Rolling Stones song before? If you answered yes to this question, then you’ve heard a IV chord. In fact, it is exponentially more difficult to find a rock/pop song that doesn’t have a IV chord than it is to find one that contains one, assuming the song uses a chord progression (riff/hook based songs often don’t have functional harmonic progressions, so these would be exempt).
Tonal vs. Modal
I, IV, and V chords (G major, C major, and D major, respectively, is the most common permutation of this in rock/pop music, largely because of the convenience from these particular chords on the guitar) are certainly the crux of rock harmony, but unlike in the classical tradition, the IV is a more important complement to I than V is. This leads to a common misconception about rock music: it is not typically tonal. By definition, tonal music requires a harmonic goal of dominant tension (usually a V chord) being resolved to tonic resolution (I). This movement of tension to release is caused by the very unstable seventh note of the scale (found in the V chord) resolving up a step to scale degree 1. Since the IV chord does not contain the seventh note of the scale, the defining tension of tonal music is not found when the most basic progression is IV – I instead of V – I. There are other reasons why rock/pop music is often not technically tonal (some of which will be covered in this series), but the diminished importance of the dominant to tonic progression is the most crucial.
Instead, most rock is best described as being modal. In modal harmony, there is a freer association of how chords move from one to another, and there does not need to be a sense of tension moving to resolution. The IV-I progression is one such example, but rock/pop music often uses progressions where the chord roots move by ascending or descending steps (I-ii-iii-IV, for example). Such progressions are often avoided in functional tonal music, but no such limitations exist in modal music. What is most important for the discussion at hand, though, is that rock/pop music is often distinguished from classical music because of its unique approach to harmonic progressions.
Examples of IV Chords in Rock/Pop Music
Even if you have no concept of chord progressions, you could probably recognize the sound of a IV chord. As previously mentioned, a IV chord typically has either predominant or plagal function. In other words, it will either move to a V chord or a I chord, respectively. While the latter is more commonly used in rock/pop music, there are plenty of examples of the former. I-IV-V progressions are the bread & butter of many punk songs, and a solid example of this is The Ramones’ “Blitzkrieg Bop”.
The chord progression for this song’s chorus (the part that starts the song) cycles a two-measure (eight beats) idea: four beats of a I chord, one-and-a-half beats of a IV chord, and two-and-a-half beats of a V chord. Since the IV moves to a V, it carries predominant function. This progression is stated three times in a row, at which point the progression shifts momentarily to another two-measure idea: two beats of a I chord, two beats of a IV chord, and four beats of a I chord. Here, the IV chord carries plagal function because it moves directly to I.
The full chorus would have the following progression, with straight vertical lines indicating measure lines and diagonal slashes indicating chord changes within a measure (this song is in A major, so the I chord is an A major chord, IV is D, and V is E):
I | IV / V | I | IV / V | I | IV / V | I / IV | I |
For examples of the plagal progression, we need look no further than The Rolling Stones. No discussion of IV chords in rock music would be complete without such a name-check. While most songs in their canon utilize this harmony, perhaps the two most recognizable are “Satisfaction” and “You Can’t Always Get What You Want”. Both songs feature I-IV-I-IV progressions prominently (though both include other chords), and this sound has become very closely associated with them as well as rock music in general.
Why IV?
I began this introductory entry (1,000+ words in, and we’re still calling this an intro?!) by saying that I think I know why rock songwriters like using the IV chord so much. I then went on to cheekily mention that it is their way of sticking it to the conventions established by concert music composers. There may be something to this – aside from the cliché of rock musicians being nonconformists, using a different approach to harmonic progression helps to distinguish the genre – but there are a couple more concrete explanations for why this chord is so prevalent in popular music from the past 50 years.
The best reason I can think of is the influence that blues music has on rock/pop music. The IV chord plays a vital role in the blues progression, and its use helps to distinguish it from other genres. While there are countless variations on the 12-bar blues, the following provides a basic template for a traditional blues progression:
I | IV | I | I |
IV | IV | I | I |
V | IV | I | V |
For an example of this progression in action, check out Sonny Boy Williamson’s “Fattening Frogs for Snakes”:
Obviously, I and IV chords are heavily weighted, but the fact that the IV chord is used exclusively with plagal function is significant (it should be noted that some versions of the blues will have a predominant chord, typically in the ninth measure moving to a V chord in the tenth measure). Also of note is the fact that the V chord moves to IV, which almost never happens in classical music. This indicates the importance of the IV chord in blues relative to the V chord: it is as if V has preplagal function rather than IV having predominant. The sound of I moving to IV, and vice versa, became pivotal to blues music, and because this music had such strong influence on early rock bands (especially The Stones), it carried equal weight in that genre, as well.
Another explanation for the prominence of the IV chord is the degree of sameness it offers, especially in regard to the melody. Consider how both IV and V chords compare to the I chord: both chords share one common tone with tonic, and those common tones are scale degrees 1 and 5, respectively. By being able to maintain scale degree 1 in the melody (which carries greater weight to it than does scale degree 5), the IV chord offers greater possibility for melodic stasis than the V.
Even when melodies don’t strictly adhere to chord tones (which they often don’t), the IV provides a more consonant option for harmonizing most rock/pop melodies. Such songs often build their melodies using pentatonic scales, which are major scales with the fourth and seventh notes removed. This removes all half steps, which in turn strips the possibility of dissonance from the melody. When comparing the pitches of the pentatonic scale with the IV chord, the only note that is considered to be dissonant to its root is scale degree 3. This pitch would be a major seventh away, but even this dissonance has grown to be acceptable in the genre, especially in this context. The V chord also has just one pitch that is dissonant with its root, but this pitch is scale degree 1. It forms a perfect fourth with the root, and while this isn’t as strong of a dissonance as a major seventh, it is only a half step away from the chord’s third. Being the most crucial pitch within any given key, this is obviously problematic. Also of issue is the fact that the two pitches removed from the pentatonic scale (four, seven) are very important to the sound of the V chord, which are the chord’s third and seventh chord tones.
This also relates to the blues, as traditional blues melodies frequently repeat phrases across different chords. A very common way to construct a blues melody is to sing a four-measure melody (which is often two measures of melody and two measures of rest, as was the case in “Snakes”) and then repeat it in measures five through eight. The final four measures of the form often present a contrasting melodic phrase, but it will occasionally be repeated here, as well. When the melody is repeated in the second phrase, it does so over the IV chord instead of the I, which works because of the similarities between these chords. Blues melodies also typically use a blues scale as opposed to pentatonic, but rock music often employs this scale, and its reliance on I and IV chords helps facilitate that.
As dissonant as some of the sounds and timbres used in rock music can be, rock music has a relatively low tolerance for harmonic dissonance. Although a V-I progression can hardly be considered dissonant, the tension created by dominant moving to tonic is often replaced in favor of the supremely consonant and largely static sound of the plagal IV-I progression.
Looking ahead
The sound of a IV-I progression is certainly very comforting and well-established in rock/pop music, but there is little inherently interesting in it at this point. However, the progression has become so entrenched in the genre that some artists have extended its application to create new and fascinating uses for the harmony. Some of these are similar to how the chord is used in classical music, but others are unique to rock/pop music, and at the very least they are used far more prominently.
This series will consist of four blog entries, with each devoted to a different way the IV chord is used in rock/pop music. Two of them will focus on specific techniques that several songs demonstrate, while the other two are devoted to how specific artists use the chord. I’m not sure when each will be posted, but here is what they will be:
- Secondary Plagal Progressions
- IV Chords & Tonal Ambiguity/Modulation
- IV Chords in Sleepy Kitty’s Projection Room
- Van Morrison’s “Into the Mystic” and the IV Chord That Isn’t There