4 for IV: Introduction

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 more »