Explained by Michael Busam
The changes to "Bonsoir Dame" are pretty "simple," but simple only in the sense that the chords are, for the most part, in the repertoire or within reach of most beginning guitarists. The verses are D-A-D-A, and the refrain is D-A-D-E7th-A-D. The nice little dreamy interlude runs Bm, Bflat, A, Bflat, A.
They seem to play the "interlude" with what I've always thought of as "short" chords, or simple barre chords. The Bm, for example: "barre" the first three strings on the seventh fret; place your ring finger on the fourth string, ninth fret. Slide up to the B-flat: ring finger goes up one fret to the eighth (this provides some of the "slidy" sounds you hear on the recording, and adds, I think, to the aforementioned "dreamy" feel); middle finger on third string, seventh fret; index finger barres the first two strings, sixth fret. Hold your fingers in the same pattern and slide it all up one fret, and you have an A chord; slide it back down a fret and you're back to B-flat, then back to A. Finally, you're back in the verse, but en medias res, so to speak: play A-D-A, rather than the full D-A-D-A.
To capture the feel of the piece you need to mimic the bass. This can be done while simultaneously playing the D and A chords, thus staying true to the rhythm of the song. While playing the D and A chords, use your pinky to play a note on the third string, fourth fret to replicate the bass line.
If you have a guitar handy, give it a shot--you'll hear the basic bass line. Now, "double" the time, so that you're playing the bass line--dum, dah, dah, dum--but working the rest of the D chord simultaneously. This is really much, much easier than it sounds!
A final note: I waffle between an E7th and Em chord in the refrain. Both strike me as possible, but I keep changing my mind!
Tom and I highly recommend playing "Bonsoir Dame" as an exercise; it really sharpens one's appreciation for the music when you sit down and try to figure what makes these "simple" little gems shine. You can really appreciate the little things that add up to the whole: a very beautiful song.