Prelude No. 1, The Well-Tempered Clavier, by JS Bach
Written by Johann Sebastian Bach, The Well-Tempered Clavier is a set of 48 preludes and fugues, 2 pairs of preludes and fugues in every major and minor key, written in two volumes. Book 1 was written in 1722; Book 2 was written in 1742. At that time, keyboard instruments were tuned according to meantone temperament, and while the fifths were more pure (though not completely pure), keys with many accidentals were out of tune in meantone tuning. So Bach wrote this collection of pieces as an essay and an argument for changing the tuning system to equal temperament.
One of the most famous preludes from the WTC is the first prelude in book 1. This piece is a perfect essay in voice leading principles and a start to a series of blog posts looking at voice leading in harmony.
The C major prelude of book 1 is made up of broken chords.
This piece is really a chorale.
We’re going to reduce these arpeggios to block chords. In doing so, it will become clear that this piece is really a chorale, and each part moves like a vocal line. Let’s start by reducing the first four bars to block chords.
You can do this on a spare piece of manuscript, or you can block these chords on the piano. Either way, it becomes clear that this is a five-part chorale. Follow the line of each part. Better yet, if you’re not shy – or when no one else is home – play through this prelude and sing along with one of the parts!
While we can analyse each chord – identifying root and quality and relating it back to the key of C using Roman numeral analysis, true understanding of how harmony works comes from experiencing how the voices that make up each vertical chord moves from one harmony to another. Notice that each voice in this phrase moves either by step up or down or stays the same. This style of voice leading is typical of the Baroque and Classical styles and represents the inner workings of what we refer to as “functional diatonic harmony”.
“Functional” >>> every note in the scale and every chord produced from those notes have a function in keeping the tonal centre (in this case, C) sounding like the centre. (You can read more about this idea HERE.)
“Diatonic” >>> just a fancy way of saying “of a key”.
“Harmony” >>> more than just “chords” and includes these operations of voice leading.
Analysing the chords, we see that this four bar phrase is a ii-V7-I progression with a perfect cadence (UK) to close it off (or an authentic cadence in the US). This opening phrase is compact, like a thesis statement for the rest of the piece, in which C major diatonic harmony and some of its chromatic elaborations unfolds.
Sequential patterns and bass movement by 5ths
Looking at the next four bars, we can see that the voice leading behaves very differently!
Soprano and alto parts leap down, up and back down in a sequential pattern. This change in voice leading invites the performer to shape their interpretation to highlight this change and to make the sequence easy to hear.
This phrase is followed by more typical voice leading, featuring smooth harmonic changes.
Notice that the end of the sequence in the third phrase is also the beginning of the fourth phrase.
Notice also that while the top voices move by step or stay the same from one harmony to the next, the bass jumps down by 5th and up again by 4th. This is bass motion by 5th (A is the 5th of D which is the 5th of G) and is typical of the Baroque and Classical voice leading style.
Sharp notes resolve up - flat notes resolve down
We get another two-bar sequence in bars 12 – 15, this time with much smoother voice-leading.
Notice that sharp accidentals resolve up by step, and flat accidentals resolve down by step. This becomes a particularly important feature in bars 22 and 23.
The F# in the bass in bar 22 and the Ab in the bass in bar 23 both act as a leading note to G. They are considered “double leading notes.” F# resolves up by semitone to G. Ab resolves down by semitone to G.
What follows is 8 bars with G (the dominant in the key of C) in the bass. This is what music theorists call “dominant prolongation”, and it happens just before a big return to the tonic (in this piece and in many others!).
Over the G, the chords change. Some of the chords match the G, but some don’t. This is called a pedal point, because it imitates what an organist does with the organ pedals.
Active score reduction
This is the perfect piece to reduce to block chords – identify the chords – analyse them in the key of C using Roman numerals. But even more important is to notice the voice leading. You can do this the long way, writing each block chord on manuscript. But you can also do "active score reduction", and play each arpeggio as a block chord. Play this piece, in reduced "block" form, a few times and choose a different part to sing along with each time. This alone will do wonders for your understanding of how voice leading works in this piece.