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It is not hard to estrange the idea of the chorus. Why should songs have some parts that are repeated and others that are not? Imagine other works of art in which a quarter or half of the work is repeated: a movie that shows the same 10-minute sequence every 20 minutes, or a book that repeats every other chapter. 

Yet, in popular music, the chorus seems necessary. It is, in many cases, the point of the song.

And now, in a wonderful essay on Aeon, Elizabeth Margulis, director of the Music Cognition Lab at the University of Arkansas, argues that repetition is the point of music. The chorus is merely our culture's embodiment of a deeper human desire to play it again.

The ethnomusicologist Bruno Nettl at the University of Illinois counts repetitiveness among the few musical universals known to characterise music the world over. Hit songs on American radio often feature a chorus that plays several times, and people listen to these already repetitive songs many times. The musicologist David Huron at Ohio State University estimates that, during more than 90 per cent of the time spent listening to music, people are actually hearing passages that they’ve listened to before. 

In fact, Margulis argues, it is repetition itself that cues us to listen musically, even if what we're hearing isn't (designed to be) music. "No matter the constituent material, whether it’s strings of syllables or strings of pitches," she writes, "it seems that the brute force of repetition can work to musicalise sequences of sounds, triggering a profound shift in the way we hear them."

Wonderfully, this also seems to explain that process whereby if you keep saying a word out loud, it begins to sound strange: lollipop, lollipop, lollipop, lollipop lollipop. Margulis argues this is because the meaning we attach to the word begins to come unmoored and we hear its sonic and qualities instead.

This is the semantic satiation effect, documented more than 100 years ago. As the word’s meaning becomes less and less accessible, aspects of the sound become oddly salient – idiosyncrasies of pronunciation, the repetition of the letter l, the abrupt end of the last syllable, for example," she writes. "The simple act of repetition makes a new way of listening possible, a more direct confrontation with the sensory attributes of the word itself.

Margulis' essay takes a fascinating turn to explain what it is about repetition that makes it so key to music. The secret, the evidence suggests, is that listening to music is an active process: We're making the music in our heads as the sounds play our brains.  

"[Repetition] captures sequencing circuitry that makes music feel like something you do rather than something you perceive," she concludes. 

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