Compositional style in the High Baroque
Four-part harmony predates Bach, but he lived during a time when modal music in Western tradition was largely supplanted by the tonal system. In this system a piece of music progresses from one chord to the next according to certain rules, with each chord characterised by four notes. The principles of four-part harmony are found not only in Bach's four-part choral music; he also prescribes it for instance in figured bass accompaniment. The new system was at the core of Bach's style. Some examples of this characteristic of Bach's style and its influence:
When in the 1740s Bach staged his arrangement of Pergolesi's Stabat Mater, he upgraded the viola part (which in the original composition plays in unison with the bass part) to fill in the harmony, thus adapting the composition to four-part harmony.
When, starting in the 19th century in Russia, there was a discussion about the authenticity of four-part court chant settings compared to earlier Russian traditions, Bach's four-part chorale settings, such as those ending his Chorale cantatas, were considered foreign-influenced musical precedents, but such influence was deemed unavoidable.
Bach's insistence on the tonal system and contribution to shaping it did not imply he was less at ease with the older modal system and the genres associated with it: more than his contemporaries (who had "moved on" to the tonal system without much exception), he often returned to the then-antiquated modes and genres. His Chromatic Fantasia and Fugue, emulating the chromatic fantasia genre used by earlier composers such as John Dowland and Jan Pieterszoon Sweelinck in D Dorian mode (comparable to D minor in the tonal system), is an example. Bach's first biographer, Johann Nikolaus Forkel, wrote of Bach's original approach to this: "I have expended much effort to find another piece of this type by Bach. But it was in vain. This fantasy is unique and has always been second to none."
Modulation, or changing key in the course of a piece, is another style characteristic where Bach goes beyond the norm in his time. Baroque instruments vastly limited modulation possibilities: keyboard instruments, before a workable system of temperament, limited the keys that could be modulated to, and wind instruments, especially brass instruments such as trumpets and horns, about a century before they were fitted with valves and crooks, were tied to the key of their tuning. Bach pushed the limits: he added "strange tones" in his organ playing, confusing the singers, according to an indictment he had to face in Arnstadt, and Louis Marchand, another early experimenter with modulation, seems to have avoided confrontation with Bach because the latter went further than anyone had done before. For example, in the Suscepit Israel of his 1723 Magnificat, he used a sophisticated compositional form in which the trumpets in E-flat play a melody in unfamiliar, variable-size quarter tones in the enharmonic scale of C minor.
The major development in Bach's time to which he was a significant contributor was a temperament for keyboard instruments that allowed their use in every key (12 major and 12 minor) and modulation without retuning. His Capriccio on the departure of a beloved brother, a very early work, showed a gusto for modulation unlike any contemporary work it has been compared to, but the full expansion came with The Well-Tempered Clavier, using all keys, which Bach apparently had been developing since around 1720, the Klavierbüchlein für Wilhelm Friedemann Bach being one of its earliest examples.
The second page of the Klavierbüchlein für Wilhelm Friedemann Bach is an ornament notation and performance guide that Bach wrote for his eldest son, then nine years old. Bach was generally quite specific on ornamentation in his compositions (in his time, much ornamentation was not written out by composers but rather considered a liberty of the performer), and his ornamentation was often quite elaborate. For instance, the "Aria" of the Goldberg Variations has rich ornamentation in nearly every measure. Bach's approach to ornamentation can also be seen in a keyboard arrangement he made of Marcello's Oboe Concerto: he added explicit ornamentation, which centuries later is still played.
Although Bach wrote no formal operas, he was not averse to the genre or its ornamented vocal style, as in his Coffee Cantata. In church music, Italian composers had imitated the operatic vocal style in genres such as the Neapolitan mass. In Protestant surroundings, there was more reluctance to adopt such a style for liturgical music. Kuhnau had notoriously shunned opera and Italian virtuoso vocal music. Bach felt differently, and a performance of his St Matthew Passion was described as sounding like opera.
In concerted playing in Bach's time, the basso continuo, consisting of instruments such as viola da gamba or cello, and harpsichord or organ, usually had the role of accompaniment, providing a piece's harmonic and rhythmic foundation. Beginning in the 1720s Bach had the organ play concertante (i.e., as a soloist) with the orchestra in instrumental cantata movements, a decade before Handel published his first organ concertos. Apart from the fifth Brandenburg Concerto and the Triple Concerto, which already had harpsichord soloists in the 1720s, Bach wrote and arranged his harpsichord concertos in the 1730s, and in his sonatas for viola da gamba and harpsichord neither instrument plays a continuo part: they are treated as equal soloists, far beyond the figured bass. In this way, Bach played a key role in the development of genres such as the keyboard concerto.
Bach wrote virtuoso music for specific instruments as well as music independent of instrumentation. For instance, the Sonatas and Partitas for Solo Violin are considered among the finest works written for violin, within reach of only accomplished players. The music fits the instrument, using the full gamut of its possibilities and requiring virtuosity but without bravura. Notwithstanding that the music and the instrument seem inseparable, Bach transcribed some pieces in this collection for other instruments. For example, Bach transcribed one of the Cello Suites for lute. In this sense, it is no surprise that Bach's music is easily and often performed on instruments it was not written for, that it is transcribed so often, and that his melodies turn up in unexpected places, such as jazz music. Apart from this, Bach left several compositions without specified instrumentation: the canons BWV 1072–1078 are in that category, as is the bulk of the Musical Offering and the Art of Fugue.
Another characteristic of Bach's style is his extensive use of counterpoint, as opposed to the homophony used in his four-part chorale settings, for example. Bach's canons, and especially his fugues, are the most characteristic of this style, which he did not invent but contributed to so fundamentally as to influence many followers. Fugues are as characteristic of Bach's style as, for instance, sonata form is of the composers of the Classical period.
These strictly contrapuntal compositions, and most of Bach's music in general, are characterised by distinct melodic lines for each voice, where the chords formed by the notes sounding at a given point follow the rules of four-part harmony. Forkel, Bach's first biographer, gives this description of this feature of Bach's music, which sets it apart from most other music:
If the language of music is merely the utterance of a melodic line, a simple sequence of musical notes, it can justly be accused of poverty. The addition of a Bass puts it upon a harmonic foundation and clarifies it but defines rather than gives it added richness. A melody so accompanied—even though all the notes are not those of the true Bass—or treated with simple embellishments in the upper parts or with simple chords used to be called "homophony". But it is a very different thing when two melodies are so interwoven that they converse together like two persons upon a footing of pleasant equality/... From 1720, when he was thirty-five until he died in 1750, Bach's harmony consists in this melodic interweaving of independent melodies, so perfect in their union that each part seems to constitute the true melody... Even in his four-part writing, we can, not infrequently, leave out the upper and lower parts and still find the middle parts harmonious and agreeable.
Bach devoted more attention than his contemporaries to the structure of his compositions. This can be seen in minor adjustments he made when adapting someone else's work, such as his earliest version of the "Keiser" St Mark Passion, where he enhances scene transitions, and in the architecture of his own work, such as his Magnificat and Leipzig Passions. In his last years, Bach revised several of his compositions, sometimes by recasting them in an enhanced structure for emphasis, as with, for example, the Mass in B minor. Bach's known preoccupation with structure led to various numerological analyses of his compositions. These peaked around the 1970s. Many were later rejected, especially those that wandered into symbolism-ridden hermeneutics.
The librettos, or lyrics, of his vocal compositions played an essential role for Bach. He sought collaboration with various text authors for his cantatas and major vocal compositions, possibly writing or adapting such texts himself to make them fit the structure of the composition when he could not rely on the talents of other text authors. His collaboration with Picander for the St Matthew Passion libretto is best known, but there was a similar process in achieving a multi-layered structure for his St John Passion libretto a few years earlier.
Among the compositional techniques Bach used, the form of the fugue recurs throughout his work; a fugue (derived from the Latin for "flight" or "escape") is a contrapuntal, polyphonic compositional technique in two or more voices, built on a subject (a musical theme) introduced at the beginning in imitation (repetition at different pitches), which recurs frequently throughout the composition. Most fugues open with the subject, which then sounds successively in each voice. When each voice has completed its entry of the subject, the exposition is complete. This is often followed by a connecting passage, or episode, developed from previously heard material; further "entries" of the subject are then heard in related keys. Episodes (if applicable) and entries are usually alternated until the final entry of the subject, at which point the music has returned to the opening key, or tonic, which is often followed by a coda. Bach was well known for his fugues and shaped his own works after those of Jan Pieterszoon Sweelinck, Johann Jakob Froberger, Johann Pachelbel, Girolamo Frescobaldi, Dieterich Buxtehude and others.
