Many consider the two books of the Well-Tempered Clavier Bach's finest keyboard collection. He completed the first volume in Cöthen in 1722 and the second around 16 years later in Leipzig. Both books consist of 24 preludes and fugues going through all the keys, a total of 48 pieces in each volume, though some recordings give 24 tracks, one for each key covered. Book 1 opens with a prelude and fugue in the following sequence: C major, C minor, C sharp major, C sharp minor, D major, D minor, etc.
The First Book is more focused in its greater stylistic unity than its successor. Most of the preludes deal with a specific technical feature, while the fugues are more varied in style and form and often seem to express a whole world of developmental possibilities for the music. The First Book's opening prelude is soothing and serene in its scalar writing, its manner of thematic flow seeming to augur the more intimate character of the first movement of Beethoven's Moonlight Sonata, written three-quarters of a century later. The succeeding fugue is also somewhat subdued in its more animated pacing and deft contrapuntal activity. The prelude and fugue that follow are livelier, the latter quite playful and charming.
But there are such vast riches in this monumental set, too many even for lengthy analysis. The E major Fugue, for example, has a delightful carefree manner in its colorful sixteenth note passages and its consistently inventive keyboard writing. The Prelude in F sharp minor has a subtlety that may not be grasped upon first or second hearing. There are sinister elements here, as well as a sense of yearning and frustration. The four-voice G minor Fugue has a muscular and heroic character, Bach's contrapuntal writing again divulging his utter mastery. The gentle G sharp minor Prelude is a beautiful piece, mixing sunshine and sadness. The A major Fugue has a jaunty, exhilaration about its lively music, its first part comprised of eighth notes, the latter of sixteenth notes. The B flat major Fugue has a sense of joy and humor in its lively manner, yet manages to achieve an expressive depth one would not normally associate with that kind of description.
Analysis of Bach's music here often runs into controversial areas, with a few musicians tailoring their interpretation according to religious symbolism they believe to be present in the score. For example, a passage in the F minor Fugue has been interpreted as representing Christ's crucifixion, owing to its descending chromatic manner and other features. In the end, this view, as well as the idea that certain numbers (representing tones or other compositional elements) symbolize other religious events, must be assessed as highly dubious speculation. The music though, regardless of how one hears it, is masterful from first prelude to last fugue.