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.

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Prelude and Fugue No.1 in C, BWV846

The prelude in C major that opens the first volume of Bach's Well-tempered Clavier may well be his most universally recognized piece of music—and yet, as fate would have it, many of those who know it have never heard the fugue for which it is a prelude, and might in fact have no idea that it is part of a larger work that counts among the most significant and groundbreaking musical efforts ever penned. Because of the mathematics involved, the tuning, or temperament, of a keyboard instrument must necessarily be only an approximation of intervallic perfection. Various methods of arriving at a satisfying approximation were tried out during the Renaissance and Baroque, but none was really successful—none produced a tuned instrument that could play in more than a small handful of keys without the result sounding grossly out of tune—until the late seventeenth century, when several satisfying methods came into general use. Now a harpsichordist could play to good effect in each of the 24 keys, and around 1722 Bach decided to compose a prelude and a fugue in each of them. Historical considerations aside, the pages of the Well-tempered Clavier are felt by many to be the most flawlessly crafted, brilliantly designed music ever composed.

The C major prelude is on the surface a most simple piece of music: a series of chords unfolds, each arpeggiated in exactly the same way. But the cleverness by which that exact series of harmonies in that exact spacing with that exact arpeggiation was devised cannot be overestimated. In fact, Bach spent a great deal of effort on this seemingly effortless miniature, and it took him more than one try to get it right—it is one of just a few Well-tempered Clavier pieces that exist in more than one version. The fugue is in four voices, and, interestingly enough, its subject is ever-present, which means that there are no episodes in the ordinary sense of the word, only a continuous contrapuntal elaboration of the subject (which is set against itself in the fugue's second half in a stretto of supreme elegance).

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Prelude and Fugue No.2 in C-, BWV847

This prelude, like its predecessor in C major, is known to virtually every keyboard student. Its first half is fast and motoric, with a little tick-tock figure occurring on the downbeats. A transitional passage brings some relief from the driven nature of the rhythm, and this dissolves into a brief toccata that retains a kinship to the earlier music even as it surges up and down the keyboard. The fugue offers surprising contrast: a studied, rather playful figure consisting of a triplet, almost a little trill, followed by two more notes. This figure repeats and spins out enough material to support a multivoice fugue, maintaining a strong presence even during an episode of otherwise generic passagework.

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Prelude and Fugue No.3 in C#, BWV848

Bach originally wrote this pair of pieces in C major, transposing them only when he needed to fill the C sharp major gap in his survey of all 24 keys. The prelude is bright, quick, and celebratory, with a fast, nattering element omnipresent either in the treble or the bass. The prelude leads almost directly into an oddly halting and irregular fugue subject that, despite its initial upswing, stumbles down the scale. Bach smoothes out the theme a bit during the free counterpoint that follows, and refuses to bring it back in its original form at the end.

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Prelude and Fugue No.4 in C#-, BWV849

This ruminative prelude would fit well into one of Bach's cello suites if it managed to establish and sustain its mood with only one line, rather than the two separate voices employed here. The piece meanders at a fairly slow pace, then gives way to a remarkably suspenseful fugal subject very slow, the player seeming to pause after each note to decide which menacing direction to take next. This is one of Bach's stile antico fugues, not "antique" enough to resort to the casual imitation common in the Renaissance, but working out the material in the patient manner of Buxtehude and his predecessors. Ultimately, the fugue becomes obsessed with a five-note figure derived from the original subject, and with this it trudges resignedly to its conclusion.

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Prelude and Fugue No.5 in D, BWV850

Here's one of Bach's brighter preludes, with a busy patter in the treble never pausing for breath; it's pricked from below by a tick-tock figure in the bass. Toward the end, the bass line joins the treble in a fuller partnership, but this quickly throws the music into a few bars of toccata-like spasms. One of those flourishes echoes in the fugal subject, a rumble followed by two dotted-note figures. This is the sort of thing that could be employed in a French overture, but Bach launches a short fugue with it, breaking the theme into its component parts during the section of free counterpoint rather than developing a full counter-theme.

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Prelude and Fugue No.6 in D-, BWV851

Bach immediately establishes a march rhythm in the bass line of the prelude, but the treble is all roiling passagework. At the midpoint, the music almost veers into a free toccata, but after only a bar or so it returns to the strict initial pattern, ending with a few assertive chords. The brief but no-nonsense fugue presents three close entries of its subject and quickly veers into free counterpoint that closely hews to the theme.

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Prelude and Fugue No.7 in Eb, BWV852

This prelude, one of Bach's best known, may be one of the earliest pieces Bach wrote for what years later became Book 1 of the Well Tempered Clavier. A short phrase in the right hand echoes in the left; this exchange is repeated several times, the phrase ascending the scale, whereupon the right- and left-hand parts gradually become more fully integrated. An unexpected, wild little run stops up short against a measured, chordal section that follows the contours of the opening melody. That melody finally reasserts itself in full and develops into a three-voice composition, two voices working in imitation and conversation while the third provides harmonic support. The piece continues in this vein at length; indeed, this is by far the most extended prelude in Book 1 of the Well Tempered Clavier. The fugue seems tiny and almost trivial by comparison; its chipper, sputtering subject enters three times, each arrival close upon the one before, and the theme soon becomes submerged in the free counterpoint. It resurfaces frequently, but only in fragmentary form.

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Prelude and Fugue No.8 in Eb-/D#-, BWV853

The prelude is at once ceremonial and tragic, a procession of widely spaced chords connected by a single, highly ornamented line. The fugue is technically in D sharp minor—there was a difference in tuning in Bach's day, although this is now obscured, particularly when played on the piano. Further complicating matters, it was originally written in D minor, and later transposed to fill the E flat minor gap in this set. Massive by Well Tempered Clavier standards, it features a sober, expansive subject that meanders in two parts for quite some time before the subject's third appearance—an entrance that fails to deliver a sustained third voice. The texture remains extraordinarily spare. Meditative and desolate, the fugue picks its way through a bleak musical soundscape, occasionally in danger of slipping into harrowing harmonic territory. Fugues are reputedly the most intellectual of musical forms, but this fugue makes a particularly emotional impression.

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Prelude and Fugue No.9 in E, BWV854

Elegant and polished, this prelude has a gentle rhythmic ebb and flow that smoothes over what could otherwise serve as an almost rustic dance tune. The clean, compact fugue, sprightly and chattering, seems designed to keep the fingers as busy as possible within a moderate, not fast, tempo; it reaches its tightly argued conclusion in less than a minute and a half.

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Prelude and Fugue No.10 in E-, BWV855

A tentative melody in the treble keens and trills over a steady but restless accompaniment worrying the bass clef; toward the end, everything seems to break into double speed, the pathos suddenly giving way to urgency. This impetus carries over into the short fugue, with its fast, driving, down-sliding subject. In less than four minutes, Bach has delivered a small musical drama that makes up in emotional effect what it may lack in structural ingenuity.

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Prelude and Fugue No.11 in F, BWV856

The prelude could double as one of Bach's Two-Part Inventions, the two independent lines tending to cover the same musical terrain in rather different ways: one hand, initially the right, undulates through the melody, squirming with notes, while the other merely picks out the bare outline of the theme as accompaniment. The material switches hands several times, and sometimes both hands engage in a little trilling contest. The prelude's pecked-out accompaniment seems to inspire the first bar of the fugue's subject, which then breaks into more involved passagework. Although this is a very brief fugue, Bach lays out its little intricacies of form with great care.

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Prelude and Fugue No.12 in F-, BWV857

This is one of Bach's most searching, questioning preludes, and imaginative use of the key gives this prelude-and-fugue pair a harmonic and textural richness. The principal melody maintains steady motion; accompaniment is sometimes chordal, but often imitative of the treble line. The slow, patient fugue begins with an eerie subject pecked out one long note at a time. This soon evolves into the true germ of the fugue, a brief, rising, three-note arpeggio, a particularly interrogatory figure that Bach almost obsessively employs.

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Prelude and Fugue No.13 in F#, BWV858

Although the left hand immediately repeats the right hand's opening phrase, this turns out not to be a canonic prelude at all; the accompaniment is a sparse series of notes on the downbeats, while a bright, easygoing melody progresses through the treble. The fugal subject, which begins like a broad, three-note fanfare, makes three entrances before dissolving into free counterpoint, with a stuttering, telegraph-like countersubject finding limited use along the way in this compact fugue.

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Prelude and Fugue No.14 in F#-, BWV859

In this prelude, a steady, moderately fast jogging tune in the treble is followed at a close distance by similar material in the bass. The fugue has a radically different character: a slow, rising three-note figure creeps in, repeats with shorter note values after a pause, and gradually forms a more elaborate, stately theme. Bach makes excellent use of those rests in the principal subject, for when the theme enters in the second and third voices, the countersubject gets underway only at the beginning of the first rest, and the listener can discern the separate voices at play more readily than in some of Bach's busier, non-stop fugal subjects.

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Prelude and Fugue No.15 in G, BWV860

Brilliant cascades of passagework rush through the little prelude, while Bach provides a bouncing rhythmic figure in the bass. The fugue's subject, with its turns and bright nature, might easily form the basis of a coloratura aria. Here, of course, it becomes enmeshed in counterpoint. This is one of the Well Tempered Clavier pieces Bach worked on the longest, and the result is highly polished, with each voice maintaining great independence while interlocking perfectly with the other contrapuntal lines.

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Prelude and Fugue No.16 in G-, BWV861

An arresting trill in the right hand extends over the first several bars of this prelude, while the bass line steps steadily if gingerly along. That enormous trill recurs several times, occasionally in the bass, but the main melodic idea is a two-note tiptoe between a triplet figure—material that the two hands trade back and forth, or repeat one after the other, even as the motive evolves into five-note figures with a single note serving as a stepping stone between them. The fugue gets down to business with close entrances of each voice, another five-note figure immediately wandering off into free counterpoint.

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Prelude and Fugue No.17 in Ab, BWV862

The brief prelude is based almost entirely on material Bach sets out in the first bar or two, a little fanfare figure announced in the right hand and echoed in the left. This provides the fodder for an ongoing conversation between the treble and bass parts, often with one hand nattering away with repetitive passagework while the other offers a more elaborate treatment of the basic motif. The four-voice fugue's angular but generally rising subject enters first in the tenor, then bass, and at length soprano and alto. Its countersubject is an elaboration of what initially sounds like little more than a rising and falling scale.

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Prelude and Fugue No.18 in G#-, BWV863

One might expect this prelude and fugue that follow those in A flat major to be in A flat minor; Bach, however, prefers to label the key G sharp minor—essentially the same thing, although the ears of Bach's time, accustomed to the vagaries of other tuning systems, would have anticipated a slight difference in character between the two. The prelude flows and rolls smoothly through a three-voice texture; the fugue employs a somewhat menacing, or at least mysterious, theme quite contrasting with the good-natured prelude. Structurally it's a straightforward piece in four voices, the subject arriving first in the tenor, then alto, soprano, and bass.

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Prelude and Fugue No.19 in A, BWV864

Oddly, the prelude in this pair is itself almost a fugue; its minuet-like opening theme makes a second entrance and begins a contrapuntal dialog with itself. Two further themes, so closely related as to barely count as separate motifs, arrive and receive similar treatment, with all this happening at a moderate tempo in less than a minute and a half. The fugue is also something of a novelty, in the unusual 9/18 meter. Its playful, peekaboo theme launches a three-voice structure, entering from the top of the keyboard down.

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Prelude and Fugue No.20 in A-, BWV865

The concise, dual-voiced prelude, dramatic and stern, is a mere appetizer compared to the meaty fugue, a four-voice work with a substantial subject announcing itself in the alto voice, then soprano, bass, and tenor. One remarkable feature of this fugue is its use of sustained notes (even though this is not a slow-tempo piece), suggesting that Bach conceived it for a pedal harpsichord or an organ with pedals (something not to be taken for granted in the private homes of Bach's day); this allows a low note to be sustained while all the fingers are free to work in higher ranges.

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Prelude and Fugue No.21 in Bb, BWV866

This pair of pieces begins with a nimble toccata, full of cadenza-like passages interrupted by typically portentous chords. For once, this is a prelude that couldn't be dropped among Bach's two-part inventions or three-part sinfonias. The three-voice fugue, on the other hand, is unremarkable except for its jaunty character, with the relatively long subject (for so compact a fugue) arriving in top-to-bottom voicings.

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Prelude and Fugue No.22 in Bb-, BWV867

Here is one of Bach's most full-bodied preludes, grave and chordal and a bit old-fashioned, introducing an intentionally old-fashioned alla breve fugue, its five voices entering in descending order and engaging in slow, sober counterpoint. Today, alla breve or cut time implies a quick tempo, but this was not always the case, and this fugue almost requires a rather slow pace; in fact, the voicings and the naturally measured tread suggest that Bach conceived this as an organ fugue, or at least wanted to evoke organ sonorities on the harpsichord.

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Prelude and Fugue No.23 in B, BWV868

The three-voice prelude's principal theme suggests a trill played in slow motion, which links it to the subject of the fugue, whose next-to-last note is an authentic trill. Or so it is upon the initial appearance of the theme in the tenor; as the subject arrives in three more voices—alto, soprano, and finally bass—the fingers are far too busy to handle a trill everywhere it should appear. Here, Bach tightly weaves his counterpoint with great expertise, although he may have put in too much time revising and perfecting the fugue's technical aspects for the music's own good; ultimately, it is rather dry compared to many of the other fugues in this set.

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Prelude and Fugue No.24 in B-, BWV869

Book I of the Well Tempered Clavier closes with some of the most ambitious music in the collection. First, the prelude may sound thin-textured, but it actually employs fugal counterpoint over a steadily jogging bass line—a far more complex piece than it may seem to the casual ear. Then comes the fugue, the longest and grandest in the set. The Largo tempo marking has something to do with the length, naturally, but the work inherently requires room to stretch out. The extended subject uses all the notes of the chromatic scale. Thus, it's a twelve-tone composition written nearly two centuries before Schoenberg championed dodecaphony, although Bach does not employ any of the techniques of manipulation Schoenberg would rely on; his goal is to write a well-ordered Baroque fugue. It's a four-voice fugue, with the voices entering in the alto, tenor, bass, and finally soprano, but as in the prelude, Bach avoids dense textures at all times.

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