The Anatomy of a Bach Chorale

After chewing over that University of Melbourne study on consonance and pitch in a few posts, I think it would be interesting to dig into consonance, dissonance and harmony from a musical point of view, rather than a scientific point of view. Thanks, by the way, to my commentor Joel for making an excellent contribution to figuring out what was going on in that study.

I have mentioned a couple of times a book that has been in print for nearly 250 years: a collection of Bach chorales put together by various people including Bach's son, C. P. E. Bach. I was just looking at it and learned that the original sources for almost half of these 371 chorales have been lost! I hadn't known that before. Just how much of Bach's music have we lost? Between his death in 1750 and the explosion of Bach performance and appreciation in the last three-quarters of the 19th century, quite a bit apparently.

In any case, what I want to do is take a Bach chorale and look at it closely to see just why Bach is so respected as the master of harmony. Luckily a suitable chorale is available on YouTube with the score. Here is "Aus tiefer Not schrei ich zu Dir" (Out of deep distress I cry to you), the concluding chorale from the cantata, BWV 38:

In the collection of Bach chorales, this one is titled "Aus tiefer Not", but you will notice that the text actually sung here is "Ob bei uns ist der Sünden viel". Bach used the text of the first part of Luther's chorale for the opening movement, and the text of the second part for the concluding chorale. Here is the first section:

It is actually clearer in the YouTube clip! Let's just walk through what Bach is doing here. The key is A minor, which has no sharps or flats. We see added sharps because in minor keys, in order to create a leading tone, we need to raise the seventh note of the scale--in this case G becomes G#. There are two short phrases in this first section. Each one ends with a held note, shown by the fermata sign (the curvy thing with a dot). This is where the singers take a breath. The two most important harmonies in a piece in A minor are the tonic triad, ACE and the dominant: EG#B. As you can see, both phrases end on the dominant. We don't get a cadence on the tonic until the second section.

Bach does something very radical at the very beginning here: he begins, not only with the dominant, but with a dominant 7th. This chord is spelled EG#BD. The D is the seventh. But the D is put in the lowest voice, the bass. When the bass note is a note other than the root of the chord (A is the root of an A chord, E is the root of an E chord, etc.), the chord is said to be "in inversion". This was a discovery (theory?) of Rameau in his famous book on harmony published in the 1720s. If E is in the bass, the chord is in "root position" if G#, then first inversion, if B, then second inversion and if D is in the bass, third inversion. The interesting thing about 7th chords in last inversion is that, since the seventh is in the bass and sevenths have to resolve down (one of those rules), then a dominant chord in last inversion pretty much always has to go to a tonic chord in first inversion. If you have a look, you will see that yes, that is exactly what happens. Then we have another dominant chord, this time in second inversion and then a tonic in root position. This is how Bach gets this strong descending bass line: D C B A. Next is a little hint of G major, but at the last instant, the harmony swerves back to the dominant of A minor. And that's the first phrase! Tricky to put into words. The great strength of music notation is that it records all this very efficiently. The second phrase begins with a strong dominant to tonic, both in root position, then wanders into C major for a bit before, again, closing with the dominant of A minor. Now it would be good to go back and listen to this first section again, trying to hear some of this.

Not counting the repeat, this first section is only about 20 seconds of music. Can you hear how strong the 'flavour' of the first chord is? How that bass note has to resolve somewhere? Bach does  much more radical things than this, of course, but this is a good sample of what goes on in a Bach chorale.

Each voice is independent and sings well. The bass line is nearly as important as the soprano melody on top and even the middle voices, the alto and tenor, are enjoyable.

The exercise of taking a simple melody, like the top line here, and writing the other three voices or "harmonizing" the melody, is one that every music student spends quite a bit of time learning how to do. This kind of smooth, flowing harmony, with occasional pungent harmonic tension, is a lot harder to write than it sounds!

So that's a little 20 second insight into Bach's harmony... If you want to listen to the whole cantata, of which this is the last movement, here it is: