Fuga a 3 Soggetti (Contrapunctus XIV): 4-voice triple fugue (not completed, but likely to have become a quadruple fugue: see below), the third subject of which is based on the BACH motif, B♭ – A – C – B♮ ('H' in German letter notation):
The Unfinished Fugue
Only the first page of the last choral prelude BWV 668, the so-called "deathbed chorale", has survived, recorded by an unknown copyist. The piece was posthumously published in 1751 as an appendix to the Art of the Fugue, with the title "Wenn wir in höchsten Nöthen sein" (BWV 668a), instead of the original title "Vor deinen Thron tret ich hiermit" ("Before your throne I now appear").
There have been various accounts of the circumstances surrounding the composition of this chorale. The biographical account from 1802 of Johann Nicolaus Forkel that Altnikol was copying the work at the composer's deathbed has since been discounted: in the second half of the eighteenth century, it had become an apocryphal legend, encouraged by Bach's heirs, Carl Philipp Emmanuel Bach and Wilhelm Friedmann Bach. The piece, however, is now accepted as a planned reworking of the shorter chorale prelude Wenn wir in höchsten Nöthen sein (BWV 641) from the Orgelbüchlein (c 1715)
A handwritten manuscript of the piece known as the Unfinished Fugue is among the three bundled with the autograph manuscript P200. It breaks off abruptly in the middle of its third section, with an only partially written measure 239. This autograph carries a note in the handwriting of Carl Philipp Emanuel Bach, stating "Über dieser Fuge, wo der Name B A C H im Contrasubject angebracht worden, ist der Verfasser gestorben." ("At the point where the composer introduces the name BACH [for which the English notation would be B♭–A–C–B♮] in the countersubject to this fugue, the composer died.") This account is disputed by modern scholars, as the manuscript is clearly written in Bach's own hand, and thus dates to a time before his deteriorating health and vision would have prevented his ability to write, probably 1748–1749.
Many scholars, including Gustav Nottebohm (1881), Wolff and Davitt Moroney, have argued that the piece was intended to be a quadruple fugue, with the opening theme of Contrapunctus I to be introduced as the fourth subject. The title Fuga a 3 soggetti, in Italian rather than Latin, was not given by the composer but by CPE Bach, and Bach's obituary actually makes mention of "a draft for a fugue that was to contain four themes in four voices". The combination of all four themes would bring the entire work to a fitting climax. Wolff also suspected that Bach might have finished the fugue on a lost page, called "fragment X", on which the composer attempted to work out the counterpoint between the four subjects. The 2016 completion by pianist Kimiko Douglass-Ishizaka rejects the fourth subject theory, opting instead to develop the extant materials in the fugue to completion.
A number of musicians and musicologists have composed conjectural completions of Contrapunctus XIV, notably Boëly, music theoretician Hugo Riemann, musicologists Donald Tovey and Zoltán Göncz, organists Helmut Walcha, David Goode and Lionel Rogg, and Davitt Moroney. Ferruccio Busoni's Fantasia contrappuntistica is based onContrapunctus XIV, but is more a work by Busoni than by Bach. In 2001 Luciano Berio completed the contrapunctus for orchestra.
In 2007, New Zealand organist and conductor Indra Hughes completed a doctoral thesis about the unfinished ending of Contrapunctus XIV, proposing that the work was left unfinished not because Bach died, but as a deliberate choice by Bach to encourage independent efforts at a completion.