Sometime near 1747, Johann Sebastian Bach began working on what will later become known as Die Kunst der Fuge. When he died three years later on July 28, 1750, the work was left unfinished. Below the unfinished nineteenth contrapunto, a quadruple fugue, his son, Carl Philipp Emanuel, writes with a good sense of drama: 'Über dieser Fuge, wo der Nahme BACH im Contrasubject angebracht worden ist, ist der Verfasser gestorben ['While working on this fugue, which features the name BACH in the counter subject, the author died']. Bach died while bent over the score from which the four final notes, bes-a-c-b, form the name of Bach in German. But wouldn't dying invite the possibility of a return? As, perhaps, a specter or a ghost?
 The notation form, in particular - four separate staves, three of which are in the C-clef and one in the F-clef - has led to a reasonable consensus as to Bach's intention for this work. Many believe that Bach had a clear pedagogical purpose in mind (cf. Heinrich, Leonhardt, Panthaleon van Eck, Schlötterer-Traimer). They agree with Johann Nikolaus Forkel's analysis from 1802: 'Incidentally, the work consists largely of variations. It was the author's intention to show what could be done with a fugal theme'. Already in 1756, six years after Johann Sebastian died, his son, Carl Philipp Emanuel, comments on the work in similar terms: 'I may be permitted to observe this much: that it is the most perfect practical fugal work, and that every student of the art, with the help of a good theoretical instruction book, such as the one by Marpurg, must necessarily learn from it to make a good fugue, and thus needs for his instruction no oral teacher, who often charges dear enough for imparting the secret of the fugue'. (From an advertisement in which Carl Philipp offers the engraved copper plates of the fugal work for sale). Die Kunst der Fuge may be understood as a concrete musical expression of insights into the composition of fugues with which Bach had familiarized himself during his life. The notation form chosen becomes understandable from the viewpoint of a teacher wanting to show clearly the development of the individual voices (cf. Leonhardt, Schlötterer-Traimer). 'Kunst' (art) refers, in this case, to 'Entwurf' (plan or concept) or 'Aufstellung' (placing or set up), a demonstration of possibilities. For quite some time therefore, the study and analysis of the work has been more highly regarded than the actual performance of it. This, in fact, elicited a musicologist to say that it is does not matter whether one listens to Die Kunst der Fuge with one's ears, or imagines the music by reading the score (cf. Panthaleon van Eck). A remarkable thought. The audible performance becomes secondary or supplementary to the written score; any concrete musical realizations may be dismissed as mere vehicles of thought. The essence of Die Kunst der Fuge is said to lie in the score, instead of the score serving as a tool, a supplement, that would bring us to the sounds.
 As is often the case with Bach's music, Die Kunst der Fuge lacks clear instruction on instrumentation, dynamics and articulation. Indeed, even the order of the various parts is not unequivocally clear. This tolerance for variation in instrumentation, for the substitution of one section by another or for varying the beginning and end points, should not be taken for mere carelessness or disinterest with regard to the choice of detail. Rather, it may represent a vast difference in perception. The earlier composers - dating from the time before the first Viennese School - took an entirely different approach toward the concept of structural wholeness - an ideal that becomes imperative only in the 19th century German music. Moreover, in Bach's day, performers knew quite well how to determine tempo and dynamic level, how to phrase the music, how to ornament, etc. For that reason, very little was written down. As a result, free areas accumulated in conventionally fixed aspects of Die Kunst der Fuge through the passage of time. White zones, so to speak, in the musical texture. It seems as if Bach frequently left his notation open as an invitation to all kinds of changes, a trait that lends both flexibility and endurance to his music. Because we are left with only 'bare' notes, many different interpretations of Die Kunst der Fuge have been produced. There are performances by a string quartet, by various orchestra strengths, by church organ, by four voices, by two harpsichords.
In the second part of his Composition as Process lecture , entitled 'Indeterminacy', John Cage speaks about possibilities that occur when parameters are lacking. According to Cage, structure, method, and form of The Art of the Fugue are all determined. (As indicated above, this statement is questionable. The order of the individual fugues is subject to change.) Frequency and duration are also determined. However, the material properties timbre and amplitude are not provided; these are indeterminate. This is what arouses Cage's special attention. With regard to the volume, he says that this indeterminacy 'brings about the possibility of a unique overtone structure and decibel range on each performance of The Art of the Fugue'. Regarding timbre, the function of the performer is 'comparable to that of someone filling in color where outlines are given'.
It may be questioned to what extent these and further remarks of Cage put Gerd Zacher on the track of his project. Although Zacher never refers to this lecture, Cage's reflections seem to have almost paved the way for Die Kunst einer Fuge. First of all, Cage explains, each performer can stay fairly close to the conventions (he mentions the transcriptions by Arnold Schönberg and Anton Webern). But he may also execute his colorist function in a way that is not conventional, and give a performance that could be called arbitrary. He can follow the dictates of his ego, e.g., his taste. Or, of his subconsciousness (as in automatic writing), more or less unknowingly employing certain operations that are exterior to his conscious mind (cf. Cage, 1961, p.35).
Could it be that Bach's music is, for the most part, independent of the performance practice conventions? Could it be that nothing is necessarily sacrificed if these conventions are not taken into consideration? Cage points out that there is considerable room for maneuver in the shaping of this music. And Zacher agrees and lets us hear the results. In a first reading which is more conventional. In nine subsequent readings in which he colors the given outlines in less conventional ways.