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Moonlight and Mode Mixture

Since I started teaching music theory online, I've discovered how much fun it can be to analyse well-known piano pieces - pieces that we've all heard a thousand times or more (especially if you teach piano, like me), to the point where they become a bit hackneyed, and we hardly notice them.

But turning an analytical eye ot a piece like that can refresh the piece and renew our vision of it! You understand why it's so popular. You start to hear it again.

And the perfect example of such a piece is Beethoven's Moonlight Sonata (first movement).

I remember in my first year of teaching, an adult student at elementary level came to her lesson one day and told me that she'd been to a dinner party at the weekend where someone had played the first movement of the Moonlight Sonata. She thought it sounded easy, and she asked if we could work on it in her lessons. !!

Well, it's not so easy as it might seem. The key of C# minor is tricky, especially for elementary level pianists, and the issues of balance, cantabile playing and expression are enormous!

I understood her request. It has the sound of being entirely accessible, to both listeners and players. But this simple surface shrouds one or two interesting and surprising harmonic turns, and that is what we will look at in today's blog post.

But first, a bit of background.

Beethoven wrote his Moonlight Sonata in 1801. The title was given to the work by a critic 30 or so years after its completion. The Encyclopaedia Britannica informs me that, "The German Romantic poet Ludwig Rellstab published a review in which he likened the first movement of the piece to a boat floating in the moonlight on Switzerland's Lake Lucerne."

Well - perhaps! This is Beethoven's 14th piano sonata, and it is most unusual for its genre. The first movement is marked Sonata quasi una fantasia ("Sonata in the manner of a fantasia"), and the style of the piece is definitely dreamy. This is markedly different to the usual first movements of sonatas of the time, where themes are well-defined within the sonata-allegro structure.

The first movement of the Moonlight Sonata is more like an improvisation, and its harmonic wanderings are remarakble.

It has a texture that makes it so easy to think about the part that voice-leading plays in making good chord progressions.

Similar to the Bach C Major Prelude I blogged about last month (which you can read about HERE), the broken chords of the Moonlight Sonata are voiced in such a way that you can imagine setting each note of the chord as a part in a choir.

If you can play this piece, it's a fun idea to pick out one of the parts and sing along while you play!

This texture also makes it easy to analyse the harmony.

The opening steps through a fairly typical diatonic progression in C# minor, featuring a falling bass line stepping from tonic to dominant and ending on a perfect cadence (perfect authentic cadence, if you're Stateside).

The second phrase sees the entrance of the melody in the top part. Developing the ability to balance a cantabile line above the inner workings of the chord progression, all played in the right hand, is crucial to the success of this piece. The phrase takes a turn toward the relative major and cadences on E major in bar 9.

Immediately following, Beethoven shifts to the parallel minor - E minor - in bar 10. This is a technique I refer to as "mode mixture". The tonic note, E, is the same, but Beethoven has expanded his palette to include E minor. Mode mixture is a great way to add chromatic colour and interest to a piece, but Beethoven uses it hear to create structure.

The third phrase cadences on B minor in bar 15. The very next beat, Beethoven again uses mode mixture and changes the B minor tonic chord to a B major tonic.

He continues to mix chords from the B major and B minor scales in the bars that follow - minor subdominant (iv) and major tonic (I).

The magic of mode mixture in the Moonlight

So in the first 21 bars, Beethoven moves through four different key signatures, and the linking element is mode mixture.

Moving from C# minor to the relative E major in bars 8-9 is pretty typical for a piece in a minor key.

But the shift from E major to E minor moves us from a key with four sharps to a key with one sharp. This is a far cry from the typical modulation to adjacent keys on the Circle of Fifths.

He's jumped three keys on the circle with a simple shift of mode.

And then he quickly does it again. The shift from B minor to B major in bar 15 jumps another three keys on the circle.

This piece is so famous, that we don't really hear these big jumps around the circle as anything particularly special, but if you imagine hearing this piece for the first time in the early 19th century, these shifts must have come as a big surprise!

Sonata structure in a free-form style

The other surprise would have been the improvisatory nature of this first movement - one that does not conform to the typical sonata form structure but sounds instead like a free-form "fantasia". Still, Beethoven does include a middle section that is underpinned by dominant prolongation in the key of C# minor before returning to the opening texture and melody.

This dominant prolongation sees the dominant pedal in the bass lasting 14 bars, creating a big build up of expectation for the return to C# minor in bar 42. What follows is a closing section that recapitulates the original melody and winds down to a sombre ending in C# minor.

If you map out the modulations of this first movement, it is striking to note the number and breadth of keys it passes through in a short time. It's almost like the entire movement is structured like a development section, with quick passes through many different keys - some of them fifth-related, some of them far-flung on the Circle of Fifths.

Beethoven wrote the Moonlight Sonata at the very beginning of his middle style period, when he was pushing the boundaries of the restrained and balanced Classical style and moving toward a more heroic, individualistic style of composition. We can see from the harmonic scheme of the first movement of the Moonlight that he has already achieved a marked personal style through these extraordinary twists and turns around various major and minor modes.

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