Listen from 0'07" to 0'33".
In the spirit of the season, let’s take a look at a bit of one of my all-time favorite Christmas songs. We’ll say this section is 8 bars of ¾ time in the key of C, played twice, but with some chord variation in the second half. The first 4 bars use a common three-chord progression, I IV V IV (in this case, C, F, G, F), with a melody made up of 3 consecutive turns with passing tones in between, moving downward. The melody is also harmonized by a second line that sounds up a diatonic third from it. In the key of C, a diatonic third is always the note two white keys to the right of the original note.
The turnaround starts on the root (bar 5), while bars 6-8 are borrowed chords, which add a lot of interesting color to the song. The first time through, these chords move up in minor thirds: C, Eb, Gb, A. The second time through, they start to move up the same way, but the last two chords move up in perfect fourths instead, and you get: C, Eb, Ab, Db. Db Major resolves resolves nicely back to C at the beginning of the section, partially because Db to C is a root motion of only a half-step. More importantly though, in the key of C Major, Db Major is a tritone substitution, meaning it performs the same harmonic function as a more common G chord would in this situation.
Music Morsels are musical fragments, collected and analyzed.