4 for IV, Part II: IV Chords & Tonal Ambiguity/Modulation

In Part I of this series, I examined the secondary plagal progression, which is a unique way in which rock/pop composers have extended the established sound of a IV-I plagal progression. Another common technique that demonstrates the evolution of the IV chord is the incorporation of tonal instability through its presence in a harmonic progression. Generally, rock/pop music is not lacking for a tonal/modal center. However, some songs use the comforting and predictable sound of a plagal progression to introduce either tonal ambiguity or a full-fledged modulation.   Green Day, “Warning”   Despite its lack of overdriven electric guitars, “Warning” is very much a prototypical Green Day song because it only uses three different chords the whole way through. Yet these three chords (one of which is a secondary plagal chord) present an unexpected analytical challenge that lends a subtle sense of ambiguity to the song’s tonality.   Except for the song’s bridge and start of its third verse (which both simply vamp an A chord), the entire song uses the following progression. For those not familiar with my notation, vertical lines indicate barlines, diagonal slashes between chords indicate multiple chords in the same measure, and lead-sheet symbols and Roman more »