This entry takes a look at Punch Brothers' "Don't Get Married Without Me" from their "Who's Feeling Young Now?" album. The transcription can be found at the bottom of the page.
Overall, this song follows a very straight-forward form of Verse 1, Chorus, Verse 2, Chorus, Bridge, Chorus. But since we're dealing with a Punch Brothers song, what happens within that simple form is anything but vanilla.
First the verse. The first verse is 16 measures long (4+4+4+4) but what makes this verse unique metrically is that the first three phrases end in an asymmetrically-metered measure. While predominantly in 4/4, phrase 1 ends with a 5/8 measure, phrase 2 ends with a 7/8 measure, and phrase 3 ends with another 5/8 measure. Only the last phrase stays in 4/4 throughout. In each asymmetrical measure, it is the text of the vocal line that seems to dictate the length of each measure.
Turning to the harmony, the first phrase moves I-iii-I (Eb-Gm-Eb) - firmly establishing the key of E-flat major - but the following phrase begins on an unusual D-minor chord (a minor vii?). The D-minor proceeds to move back and forth with a B-flat chord, revealing that same I-iii-I progression but this time in the the key of B-flat major. The second phrase ends on a B-flat major chord, conveniently functioning as a V of the E-flat major chord that begins the third phrase. The last half of the verse mirrors the first half in the harmonic scheme yet with some quirky alterations (Eb augmented? yep.) but makes a drastic move to a new key area in the last measure of the verse. The final progression in the verse is Bb-Dm-G7 (I-iii-V7/ii). The surprising G7 chord actually functions as a chromatic pivot chord modulation that leads us to the chorus in the cheery key of C major (G7 is the V7 in C major). It should be noted that just like in "Magnet", the Punch Brothers like to move to keys related by a third away (E-flat to C).
Onto the chorus. Locking into a happy chunk-chunk-chunk-chunk rhythm, the chorus remains in 4/4 and C major throughout. While the quarter-note pulse remains the same as from the verse, the chunk-chunk rhythm creates a double-time feel that coupled with the more active and higher vocal line (notice both the extended vocal range and syncopated sixteenth-note rhythms in comparison to the lower and less rhythmic vocal line in the verse) causes the chorus to spring to life. Since some of you probably remember the overall form and know that the song moves back to the verse in E-flat, you're probably wondering how the Punch Brothers get from C back to E-flat. You guessed it, they get back to E-flat through another chromatic pivot chord modulation. The chorus ends with a move from Ab+ to Bb - an alteration of the common bVI-bVII progression - that would usually end on C. However, this time the B-flat acts like a V in the key of E-flat, resolving to an E-flat chord on the word "me". This surprising yet satisfying modulation really helps punctuate the title line of the song. Like the ex-girlfriend in the song, the music is moving on with its life - in a new key, at that! - while the singer pleas with his ex, somewhat desperately, to at the very least not get married without him.
And now to the piece de résistance! The instrumental bridge is where one is truly tempted to say "What the Punch?!?" While the bridge remains entirely in 4/4, the syncopated rhythm disrupts the steady pulse. Further disorienting the listener is the apparent random chords played on those syncopated rhythms. Yet, they're not random - strange, yes - but not totally random. Upon closer inspection, it can be seen that the bridge contains a 4-bar progression that is then repeated a minor third lower - yes, another thirds relationship! The chord progression in question is: Gm-Edim-B-G#m-B-Eb+ followed by it transposition a minor third away: Em-Dbdim-Ab-Fm-Ab-C+. Functionally speaking, this progression does not follow the rules and can be interpreted a number of different ways. Two things that I will note:
1) The Edim7 can be respelled as an A#dim7, making it the leading tone of the B chord that follows. Analyzed in B-major, the progression would be bvi-viio7-I-vi-I-III+. Labeling the Gm chord as a bvi is still weird but that's one way to look at it.
2) While the move from Eb+ to Em between phrases seems disjunct, it is actually quite smooth since both chords share two chord-tones between them (G and B enharmonically spelled). Not only that, but the Eflat sliding up to E leads to a strong sense of arrival, similar to a leading-tone rising to tonic.
Again, this bridge is thorny and difficult to break-down functionally but the important take-away is that it is just one four-measure phrase that is repeated a minor third lower.
One last thing...Chris Thile sings a whole-tone scale at the end of the bridge. Let's not fool ourselves and think most pop acts are doing that!
Here's the complete lead-sheet transcription: Don't Get Married Without Me
Also, check out this video to hear how tight those sixteenth-note sixtuplets are live (spoiler alert: they're tight!).