“The Well-Tempered Clavier (Das Wohltemperirte Clavier), or Preludes and Fugues through all the Tones and Semitones, both as regards the major third or Do Re Mi and the minor third or Re Mi Fa. For the profit and use of musical youth desirous of learning, and for the particular diversion of those already skilled in this study. Composed and completed by Johann Sebastian Bach, formerly Capellmeister and Director of Chamber Music to the Prince of Anhalt-Cöthen. 1722.”

In the first half of the 18th century, it was not yet possible to implement equal temperament in the modern sense (a tuning system where the frequency ratio of each of the 12 notes in an octave is the 12th root of 2). However, it is said that Bach, at least, “learned to tune his instrument so that all 24 keys could be played cleanly” (Forkel). There is no doubt that this collection was compiled as a pedagogical work, similar to the Inventions. Yet, at the same time, it embodied the grand idea of traversing the entire musical world using all keys. To grasp the universal order of “the world”—this was the ultimate theological challenge sought throughout the 16th-17th centuries. The Well-Tempered Clavier is thus a small, complete “world” (microcosm) that reflects God's order.

How can this be musically confirmed?

Each key is assigned one prelude in a free style and one fugue in a strict style. In most cases, however, these have little connection beyond their shared key. They are not even opposing terms like “free” and “strict,” nor is a prelude literally an “introduction” to a fugue. The preludes exhibit an extremely diverse range of old and new compositional styles, forms, and genres. Similarly, the fugues vary from simple or relatively free compositions to those that explore the limits of strict counterpoint. Nevertheless, each piece maintains its position within the world of 24 keys, forming an overall order. This is precisely “unity in diversity,” and it is the very image of “the 'world'.” The Well-Tempered Clavier is, of course, not a collection intended to be played through all 24 keys at all times. Yet, any single piece extracted from it embodies a corner of “the world.”

Here, we must consider the concept of “key character.”

Mattheson, a Hamburg musician contemporary with Bach, repeatedly warned against the rigid idea that each key expresses its own absolute character. Nevertheless, he attempted to characterize them, for example: “solemn and noble” (D minor), “extremely refined” (F major), “rough and stubborn” (C major), “sharp and stubborn” (D major). Bach also considered these common perceptions of each key and, furthermore, for the first time assigned specific characters to keys that were largely unfamiliar at the time—simply put, those with many sharps or flats (though some pieces were transposed from their original keys and added to the collection, and as Mattheson stated, one must not ignore the expressive diversity of keys). To gain a further perspective on the theory of key character, one needs to survey Bach's entire oeuvre, including his vocal works. However, in The Well-Tempered Clavier, Book I, at least, it can be said that sharp keys tend to be brilliant, and flat keys tend to be gentle.

The composition dates from 1720-22, during Bach's tenure in Cöthen and the period when he began instructing his eldest son, Friedemann, in music. Eleven original preludes can already be found in Friedemann's music notebook. The fair copy was made in 1722. Throughout the 18th century, it was widely disseminated through manuscript copies and was thoroughly studied by Mozart and Beethoven. The published edition appeared in 1801, the year marking the beginning of the 19th century, simultaneously from three publishers in the German-speaking world: Forkel edited it for Hofmeister & Kühnel (later Peters) in Leipzig, Schwenke for Simrock in Bonn, and Nägeli himself for Nägeli in Zurich. This publication marked the beginning of the Bach Renaissance (incidentally, Forkel published Book II first due to a publishing error).

*Please also see The Well-Tempered Clavier, Book II.