Niedt’s use of the term Invention for a pattern developed on a given harmonic formula has another resonance in Bach which draws further prototypes into the orbit of the prelude. The (two-part) Inventions and (three-part) Sinfonias, as they were called in the final version of 1723, had the headings Praeambulum and Fantasia in the Clavier-Büchlein.10
Although all the Inventions are constructed on standard late-Baroque harmonic progressions such as the circle of 5ths and so on, as in Niedt’s figured basses, the first three (in the sequence in which they appear in the Clavier-
Büchlein: C major, D minor, E minor) develop linear, scale-based motifs in an
obviously contrapuntal way. But there follows a series using arpeggio-based motifs whose beginnings seem designed to demonstrate standard harmonic opening gambits:
No.4 (F major) decorates just the tonic chord;
No.5 (G major) opens with the next simplest progression, I V I; No.6 (A minor) does the same, but with a suspension in the bass;
No.8 (B flat) uses the common four-chord formula, over a tonic pedal 53,64,
74 2,35;
No.9 (A major) has a circle of falling 3rds;
No.10 (G minor) is based on the descending chromatic tetrachord (lamento bass) which in itself can imply a circle of 5ths.
Similar opening gambits are demonstrated in the Book I preludes: the
progression noted in the B flat Invention (No.8) opens the preludes in C minor, D minor, F major, G major, and closely related ones open those in E minor and A minor; another very common four-chord progression (I II2V65I) opens the prelude in C major; and a further one (I I6II7V7I) that in D major. The Inventions range from relatively straightforward harmonic decoration (F major, G major) to highly ingenious motivic explorations in double counterpoint (G minor, F minor) and finally canon (C minor), all under the heading Praeambulum. Judging by the first ten items in the Clavier-Büchlein, of which some are entitled Praeambulum, some Praeludium, Bach regarded the terms as interchangeable. Thereafter he probably used Praeambulum for what were later to become the Inventions simply to distinguish them as a different series from the Praeludia which later became part of Book I, rather than because he intended some particular nuance of difference between the terms. The Inventions were to demonstrate techniques of motivic development strictly in two parts; the Praeludia began as finger-technical exercises. That Bach had no particular attachment to Praeambulum as a genre title is evident from his dropping it in favour of a term which more exactly expressed his intention, that is of demonstrating how to discover and develop good ‘inven- tions’ in Niedt’s sense. Likewise the term Fantasia could cover a very wide spectrum, from highly premeditated and ingenious examples of stile antico counterpoint, for which it was used by seventeenth-century composers such as Frescobaldi and Froberger, to pieces in the tradition of fantasiren (improvising in a free and unpredictable style) such as Bach’s own Chromatic Fantasia (Schleuning 1971 I p.13). This ambiguity probably made it seem suitable for the three-part series: contrapuntal pieces that were obviously neither fugues, ricercars, nor canzonas.11 The switch to Sinfonia, with its implications of instrumental ensemble music, underlined their function of cultivating playing in three obbligato parts.
Bach was here grappling with problems of terminology in the context of a long and complex tradition, comprehending a wide range of instrumental forms and techniques, and drawing on different national styles and local usages. In addition, the development of tonal harmony, with its radically different concepts of musical structure from what had prevailed for much of the seven- teenth century, had undermined the neatness of the old categories. The fact that he sought exact classification for different types of piece, and changed his terminology accordingly, indicates the scientific fastidiousness of Bach’s mentality. But, significantly, there were in reality no exact terms for what he intended so that it was the function, not the form, of a type that became its definer (Stauffer 1980 p.2).
The terms Praeludium and Fuga, used in Book I, were convenient in implying a contrasting pair of pieces, one free in the sense of being undefined in genre, the other strict in observing the conventions of fugal exposition and
generally staying in a set number of parts. Bach’s changes in terminology in the Inventions imply that the term Prelude could cover ingredients of fantasia, sinfonia, or sonata, as well as freely improvised pieces, or ones figured out over standard bass progressions, and this freedom suited his purpose ideally.
Of the preludes in Book I that are similar to the Inventions and Sinfonias, only the A major (in 3 parts) would be able to take its place among them. The preludes in F sharp major and G major have the qualification of being strictly in two parts but there is no real inversion of material, a fundamental charac- teristic of the Inventions. The two-part preludes in C sharp major and F major and the three-part ones in G sharp minor and B major have freedoms of texture which would exclude them. In the Book I preludes Bach therefore seems to have had similar practical and compositional objectives to those worked out in the Inventions, but in a freer framework than he allowed himself there. The preludes in F sharp minor and B major are built up from the sort of finger-exercise patterns used in the inventions in C major, D minor, and E minor; the prelude in A flat major is in the same violin-sonata manner as the B minor invention.