6 Preludes to Fugues by J.S. & W.F. Bach for String Trio (K. 404a) in D minor
ヴォルフガング・アマデウス・モーツァルト作
Mozart’s 6 Preludes to Fugues by J.S. & W.F. Bach (K. 404a), assembled in Vienna in 1782, is a revealing document of his mid-career fascination with Baroque counterpoint. Scored for string trio (violin, viola, and cello), these pieces show Mozart not as an inventor of themes, but as a masterful translator—clothing Bach fugues in a classical string idiom while supplying newly composed preludes as expressive portals into learned writing.
Background and Context
In 1782—Mozart’s first full year as a freelance composer in Vienna—his chamber music expanded in two seemingly opposite directions: toward the public brilliance of the new Viennese style, and toward a private, scholarly engagement with older contrapuntal models. K. 404a belongs decisively to the second category. It is not a set of “Mozart fugues” in the usual sense, but a curated cycle of fugues by Johann Sebastian Bach and Wilhelm Friedemann Bach, arranged for string trio, each preceded by a prelude that (in most cases) Mozart newly composed to “frame” the fugue for classical ears [1].
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This repertory sits near the center of a well-documented Viennese phenomenon: Mozart’s growing admiration for J. S. Bach’s craft, stimulated by circles that cultivated Stil and Gelehrsamkeit—learned counterpoint—alongside modern taste. One may also hear this fascination resonating through Mozart’s major chamber works of the early 1780s (for example the “Haydn” quartets begun in 1782), where fugal and canonic techniques appear not as academic display, but as dramatic, high-stakes musical rhetoric [2]).
K. 404a deserves attention precisely because it shows Mozart’s musicianship in the act of listening: how he studies, adapts, and re-voices another composer’s syntax—then makes it speak with Viennese clarity.
Composition and Dedication
The set is catalogued as K. 404a (K\u00f6chel 9) and is generally placed in Vienna, 1782—when Mozart was 26 years old. The title commonly given in modern editions (Preludes and Fugues, or Sechs Pr\u00e4ludien und Fugen) reflects its hybrid authorship: the fugues come from Bach sources (J. S. Bach and W. F. Bach), while the preludes function as Mozart’s additions and transitions [1].
Instrumentation (string trio) [1]
- Strings: violin, viola, cello
The fugues themselves are arrangements/transcriptions rather than original fugues composed ex nihilo. That distinction matters: Mozart’s artistry here lies in selection, adaptation, and the tonal-dramatic “lead-in” provided by the preludes. In this way, K. 404a acts almost like a set of miniature concert programming notes—except that the “notes” are music.
Form and Musical Character
K. 404a is best understood as six paired panels: a prelude (often slow, Adagio in character) followed by a fugue. The overall profile is not virtuoso chamber display, but concentrated contrapuntal dialogue.
Movement plan (pairs):
- No. 1: Adagio – Fugue (D minor) [1]
- No. 2: Prelude – Fugue
- No. 3: Prelude – Fugue
- No. 4: Prelude – Fugue
- No. 5: Prelude – Fugue
- No. 6: Adagio – Fugue (F minor) [1]
(Individual keys for Nos. 2–5 vary by source and edition; modern scores and parts typically present the complete set with each pair’s tonal scheme.)
Mozart’s “classicalizing” of Bach
Arranging a fugue for string trio is not a neutral act. Keyboard counterpoint (where multiple voices can be sustained and balanced by a single player) must be redistributed across three bowing instruments with their own constraints: resonance, attack, and the need to breathe between gestures. Mozart’s solutions typically involve:
- Voicing and registral clarity: lines are allocated so that entries and countersubjects project distinctly in violin/viola/cello space.
- Harmonic reinforcement: cadences and pivotal harmonic turns are underlined through string sonority rather than keyboard figuration.
- Textural pacing: episodes can feel more “spoken” on strings—Mozart often encourages this by letting the prelude establish a rhetorical tempo before the fugue’s strictness begins.
The preludes are the crucial Mozartian signature. They do not merely fill time; they establish affect (Affekt) and tonal gravity. In practice, they function like a prologue in opera: they prepare the listener’s ear for an argument that is already in progress (the Bach fugue), supplying the emotional and narrative premise that a purely “imported” fugue might lack in a Viennese salon.
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Why D minor matters
The work is frequently identified by its opening pair in D minor, a key Mozart reserved for heightened seriousness and dramatic intensity. Beginning the cycle this way lends the set an unexpectedly weighty profile: K. 404a is not a casual anthology, but an encounter with counterpoint as a moral and expressive discipline.
Reception and Legacy
K. 404a has remained a connoisseur’s corner of Mozart’s chamber output: admired by performers and listeners who enjoy hearing Mozart “in study mode,” yet rarely programmed beside the great string quartets and quintets. Its status as an arrangement contributes to that marginality; audiences often approach Mozart expecting thematic invention rather than curatorial re-imagination.
And yet, this very quality is its historical value. The set documents the late-18th-century rehabilitation of Bachian counterpoint—no longer merely a pedagogical relic, but a living resource for classical composers. In Mozart’s hands, the fugue becomes not antiquarian craftsmanship but a dramatic medium, capable of tension, release, and character; the string trio medium intensifies that sense of three distinct personalities in debate.
For modern listeners, K. 404a offers a double portrait: of Bach (and W. F. Bach) through Mozart’s ear, and of Mozart through the discipline of Bach. Few “supplementary” works in the K\u00f6chel catalogue provide such a direct window into Mozart’s compositional workshop—and into the moment when Viennese classicism reconnected itself, consciously and creatively, with the Baroque past.
[1] IMSLP: score and work page for Mozart, Preludes and Fugues, K.404a (instrumentation and overview)
[2] Wikipedia: overview of Mozart’s “Haydn” quartets (context for Mozart’s Viennese chamber style and contrapuntal interests)