Music theorist Richard Cohn has made the case that progressions like this earn their otherworldly signification because one cannot understand both the horizontal voice-leading semitones as diatonic minor seconds—a common default—and the vertical harmonic intervals as diatonic consonances. In the notation above, the triads are spelled diatonically, but the alto’s voice leading (C#-C-C#) is not, as highlighted with the dashed lines. This line could be spelled diatonically as C#-B#-C#, which would make the melodic intervals diatonic, but this would prevent the F-major triad from being spelled diatonically, as shown below; again, the dashed lines indicate non-diatonic intervals. To quote the Ninth Doctor Who: “You push one problem under the carpet and another one pops out on the other side.” This progression is simply too chromatic to hide all of it—both its chords and its lines—under diatonic carpets.
This sense that understanding a harmonic interval as commonplace keeps one from understanding a melodic interval as commonplace, or vice versa, jibes nicely with the deceits in The Good Place. However, the deceits of the first season’s last episode took the very notion of deception to another level. Likewise, The Good Place’s ident music is not your typical diatonic-interval-frustrating chromatic-mediant progression, for two reasons.
First of all, at least in nineteenth-century art music and mainstream screen music, many, and perhaps most, chromatic-mediant progressions are purely diatonic in both their vertical and horizontal intervals in their outer voices. For example, in the realizations above, the outer voices only use As, Es, and Fs, which form perfect fifths, octaves, major thirds, and minor seconds. (Same with the “Panem National Anthem” linked to above, and countless others.) Therefore, the deceit usually involves only one or more inside voices, like the alto voice above. Unlike the more conspicuous outer voices, inner voices more easily shutter the irreconcilability between horizontal and vertical away from prying ears. In other words, in the realization above, a little of the progression may not fit under a diatonic carpet, but the exposure is slight, pushed toward a dimly lit corner of the room.
A permutation of the upper voices that puts the C#-C-C# in the top voice, as shown below, would call more attention to this exposure. Perhaps because of this attention, this melodic line is not used as often for this harmonic progression.
Second of all, while it is reasonable to assume a default of a minor-second interpretation for a semitone, it does not take much to override this default. Take a purely ascending or purely descending motion through a chromatic scale, like the one below. Most composers and listeners would notate and understand nearly half of its intervals—around 42%, to be more exact—as augmented unisons (the 5 out of 12 slurs below the line) instead of minor seconds (the 7 out of 12 slurs above the line).
But what if the voice leading used the same intervals as those of the harmonies? This would avoid any double standard of diatonic reckoning. This is exactly what we get with the ident music for The Good Place, as shown below. Not only are the outer voices involved in the diatonic irreconcilability, but the top line—played by the oboe—leaps directly from C#5 to the white note four semitones higher, while the bass leaps from A down to F (best spelled as such since the A remains a common tone). Either this new note is an E#5 and the melody uses a diatonic major third but the harmony contains an augmented seventh...
...or the new note is a F5 and the harmony is diatonic but the melody spans a diminished fourth.
I remember hearing this music for the first time and disbelieving that it was an F-major triad, so strong was my sense that the oboe was playing an E# in a consonant major triad. Here was a rare realization of this progression indeed, one that uses voice leading to cover as much “surface area” on a line of perfect fifths as the harmonic progression allows: in the bass, the flattest note in the A major harmony (A) moves down a major third—which is the one directed consonance that transports a note the farthest in a flatward direction—and, in the treble, the sharpest note in the A-major harmony (C#) moves up a major third—which is the one directed consonance that transports a note the farthest in a sharpward direction. The result is music that fits even less well under diatonic carpets than standard realizations of the progression. It’s no wonder certain deceits were exposed at the end of Season One.
What is even more remarkable is how this music compares to, and contrasts with, the music that plays right as the biggest deceit of all is revealed toward the end of the final episode: although it uses a transposition (by major third!) of the same down-by-major-third progression, both its harmony (consonant triads) and voice leading (all moving voices move down by major third) are entirely diatonic, as shown below. No deceits here (apparently).