Analysis Break: Bach BWV 542

Prelude/Fantasie and Fugue in G Minor, BWV 542

Today we'll examine only a tiny fragment of a large and important work, J. S. Bach's Prelude (a.k.a. "Phantasie" or "Fantasy") and Fugue for organ in G minor. Because of the complexity and length of the piece, we'll only perform a close-up on a tiny fragment. The fragment in question is very brief, yet it provides ample food for thought. (This exercise today is more mechanical than philosophical, though we'll expound on the relationship between the two at some length in a future post.)

There are numerous recordings available, here's one:

https://www.youtube.com/watch?v=JxNR5D8TAMI

I'm going to specifically address what happens here (this segment of Music I will be calling "the excerpt" in the discussion below):

https://www.youtube.com/watch?feature=player_detailpage&v=JxNR5D8TAMI#t=194s

Pay special attention to you hear from 3:58 - 4:50.

The Fundamental Motive

An important idea that's introduced early in the piece (it's heard at the beginning of the exerpt in the second link above and but also at 1:30 and many places elsewhere) consists of a diminished arpeggio (two minor thirds) followed by a stepwise ascending motion:

Here's the example played by itself: Example1.

This figure can also be called a "motive" or a "theme" -- both words identify the musical idea as a basis for the rest of the composition. In this case, the fundamental building blocks of the rest of the piece are contained or foreshadowed in the contours of this musical idea. Let me identify them in the example below, which shows the motive with some color highlights:

I've identifed some important features:

  • The interval of a diminished fifth (i.e., f -> b-natural) identified with a red bracket
  • Several minor thirds (e.g., f->d, b->b-natural) identified with green brackets
  • A neighbor-note figure that descends a step, then reverses direction and ascends through a fourth (purple line). More generically, it can be represented as any fourth- or fifth- motion that ends with a stepwise change of direction (hence the two outlines in purple, above).

Remember the composer's aim is to create a unified work, emboyding a structure that is consistent and logical on the micro-level (such as what we see in this motive) and on a larger level (as we'll see below).

The Barberpole

Listen to the excerpt above. After a quiet passage (where we hear the motive in imitative counterpoint) a contrasting and deliberate forte section is heard where the pedal/bass notes seem to be falling, while the upper voices move upward in contrary motion. This arresting and sublime passage seems to contrast strongly with the rest of the work, and forms a type of climax--perhaps the most central message of the composition.

The bassline is notable because Bach completes several stepwise descents through the octave. The actual note names (pitch classes) used creates an endless descent through the pitches: D C Bb A G F Eb D C Bb Ab G F Eb Db C. Because of the limitations of his instrument (and human hearing) he uses octave displacement to "leap upwards" an octave periodically, which maintains the sense of "eternally falling" without running out of bass pitches. The register of the pitch changes, then, but the note names are still part of the descending scalar sequence. Here's an idea of how it works:

--I've left off some of the rest of the example, but you get the idea.

This type of technique is sometimes called a "barberpole," a visual metaphor that evokes something spinning while constantly descending:

(On a side note: This special and rare technique appears sometimes in popular music (consider this similar example: http://www.youtube.com/watch?v=8g3-7M51Tns). In the case of Jobim's "Waters of March" (Aguas de Marco) some have associated its ever-descending motion with the inevitability of death and the end--metaphorically, the end of summer [in the Southern hemisphere, March is in Fall], a suggestion of death. Is that what Bach is implying here? It might not be completely impossible, given the eschatological nature of Christian Theology.)

There's a special, structural logic that drives the operation of this bassline. It's not just a repeating, descending scale, but it begins at a different starting point each time. Remember the contour of the original motive (think purple), and recall the neighbor motion with the ascent of a fourth. Bach changes the register at certain points in his descending scale, outlining that very motive at a larger level--though inverted--as we can see here:

The whole purpose of the "barberpole bassline," then, is to connect the starting pitch D, to its destination, the B (then later inflected to B-natural) over the course of several measures. Along the way the bass outlines an interval enharmonic to a diminished fifth (see above, red brackets), D-Ab. This larger-scale "working out" of that idea is coupled with another, opposite gesture in the upper voices, as we'll see next.

Contrary Motion

As the bassline works through its descending figures, the upper voices are moving upward, often chromatically. This creates a great effect and is certainly arresting. Harmonically, Bach is traversing the circle of fifths, mixing modes (between major and minor).

I've identified the chords and how they interact with the bassline below. Note the root movement through the circle of fifths: D-G-C-F-Bb-Eb-Ab-Db:

Here's an audio version of the reduction above: Example2.

Bach manages to hit nearly every major or minor chord in the book, though the final expected chord (Gb) is avoided, and instead we reach the "arrival point," the unstable g-dim7 chord.

Interestingly enough, there's a contrapuntal element that governs the action in the upper voices--Bach isn't merely playing chords through a circle-of-fifths chart, but is actually imitating one of the features (the ascending minor third, here spelled chromatically) heard in our initial motive! I've marked the appearances of this minor third in the excerpt below, with slurs. I've also left the bassline out for the moment, so we can more clearly see how the upper voices operate.

Beneath the excerpt, I've also marked how these smaller events are played out in a larger scale, over the course of many measures. The "soprano" and "alto" voices in this case, work out in a structural way, two motivic elements: the diminished fifth (green) and the neighbor figure (purple).

Compare this "up a fourth then down" shape with the "down then up" shape heard in the working-out of the barberpole bass. They move in contrary motion (the upper voices move up, the lower voice moves down), mirroring one another.

Summary: Many Operations, Serving One Purpose

Even in this brief inspection, we're able to observe multiple techniques operating independently, yet all in service of the larger structural goals:

  • The dramatic element of the "Barber-pole" bassline,
  • Working-out of various elements from the piece's central motive over a large span of time,
  • Contrapuntally exposing motivic fragments in multiple voices, and
  • Harmonic direction (circle-of-fifths progression).

Bach would never say that music of this complexity and beauty is the Gospel, however, I can imagine someone saying that this music points toward the Gospel--he himself dedicated his works "Soli Deo Gloria" (to the Glory of God) and by all accounts viewed his Music as a vehicle to, or a support of, the Word. (I believe the complex interlockings of these various techniques form an earthly, sacred simulacrum of God's universe, but that essay is forthcoming).

Bach's Lutheran convictions and skill provided the inspiration for the next two centuries of Sacred Music.

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