Chopin wrote a series of 24 preludes for the piano, somewhat reminiscent of Paganini’s 24 caprices for violin. Each of the preludes is in one of the 24 keys that exist in the Western tonal system of music, and each one represents a different thought or emotion (although Chopin inexplicably never attached names or titles to any of the preludes). It is thought that Chopin wrote his etudes as homage to Bach’s Well-Tempered Clavier or his collection of 48 preludes for piano. However, Chopin departed from Bach’s precedent in one particularly important aspect: whereas Bach’s preludes were written in every key in ascending order of semitones (A, A sharp, B, B sharp, C, C sharp, etc.), Chopin wrote his preludes in a pattern called the “circle of fifths.” In this pattern, he would write one prelude in a major key (G Major) and write the following prelude in the relative minor key of that key (E Minor). Every prelude, then, was either a new major key or the relative minor of the previous key (C Major – A Minor, F Major – D Minor, etc.). Some scholars, therefore, have hypothesized that these preludes were never actually meant to be played in order, as is the usual practice, but rather played as individual precursors to larger works in that particular tonal center.
At the time of their composition, these etudes were somewhat controversial. Most of Europe was still making the transition from the Classical era (Mozart and Beethoven) into the Romantic era (Chopin and Liszt), and the short, improvisational nature of Chopin’s etudes pushed the boundaries of the current public perception of acceptable music. However, over time they have become some of the most well-loved and popular pieces ever written for the piano.