What is... Moto Perpetuo?

Stephen Johnson gets to grips with classical music's technical terms

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What is... Moto Perpetuo?
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A perpetual motion machine is an impossibility.

To entertain the notion is to sin against at least two of the Laws of Thermodynamics. And even if you could create some kind of Escher-like time loop, the idea of a violinist playing Paganini’s Moto perpetuo or Rimsky-Korsakov’s Flight of the Bumble Bee endlessly is hellish – and not just for the performer.

Yet there’s something about a brilliantly played Moto perpetuo that can be like sampling a small slice of eternity. On YouTube there’s a film of Yehudi Menuhin in 1947 dispatching the Paganini in an eye-watering three minutes, and looking so laid back that you have to keep checking his fingers to make sure he’s actually playing.

The pianist probably has a similar feeling as he plonks his way through the numbingly simple chordal accompaniment. But it’s Menuhin’s godlike insouciance as the notes stream out of him that gives the feeling that one is actually beholding the impossible.

The Paganini is the archetypal Moto perpetuo: rapid in execution, with all the notes of equal length (ie as short as possible) and without the merest hint of a pause for breath. In itself it’s intoxicating, mesmerising, but a pure display piece nonetheless.

But there are examples of Moto perpetuo (or Perpetuum mobile) that achieve something more. The brief Presto finale of Chopin’s Second Piano Sonata is impressive enough in its own right.

But as the final stage of a substantial, darkly introspective, death-haunted journey it seems to signify much more: a release of long-accumulated tension, yet a strangely enigmatic one – especially in the way it sputters out at the end, with a final ff chord – alarmingly like a giant hand swatting a crazed bluebottle. 

The finale of Beethoven’s D minor Piano Sonata, Op. 31 No. 2, (known as ‘The Tempest’) is a Moto perpetuo, much of the rapid motion passing equally between the hands.

But at the climax Beethoven interrupts the flow to devastating effect. A pathetic downward run suddenly accelerates, fortissimo, followed by a brief but telling silence. Something has broken, irrevocably.

Did Schubert have that at the back of his mind when he penned his youthful masterpiece Gretchen am Spinnrade? The regular movement of Gretchen’s spinning wheel suddenly stops as she remembers Faust’s kiss – and our hearts stop with her.  

This article was first published in the May 2012 issue of BBC Music Magazine

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