The structural design is in two repeated halves, the second of which is considerably longer. The time signature is twelve-sixteenth, a compound meter reminiscent of the gigue. The uninterrupted flow of sixteenth-note and frequent "gigue-rhythm patterns" (eighth-note + sixteenth-note, see e.g. in the first halves of bars 2, 3 and 4 respectively) enhance the impression that this prelude is composed along the lines of the Baroque dance which traditionally closed a suite.

An analysis of the material presented in this prelude reveals several smaller sections which are utterly important for a correct structural assessment of the piece in spite of not being harmonically concluded. It is therefore advisable to describe the design of this prelude on the basis of combined observations of harmonic processes and material presentation.

There are twelve (four + eight) sections in this prelude:

The inverted mordent poses no problem with regard to its pitch since it is immediately preceded by D which also serves as its lower neighbor note. The fact that this ornament appears in brackets points to its origin not from Bach's manuscript but from a copy. While it is thus left to the performer to include or disregard the ornament, adopting it is, in fact, a very good idea as it can be of great help for the listener in distinguishing the manifold versions of the main motive, all of which begin with scale portions and are thus difficult to discern. If the inverted mordent is incorporated in bar 1, then a similar ornament should be transferred to all bars which contain the version of the motive in which the sixteenth-note scale segment is complemented by three dotted eighth-notes in reverse motion. Such transferal is then advisable for bar 3 (L), bar 5 (U), bar 8 (L), bar 49 (U), possibly bar 52 (U, i.e. on A), bar 65 (U), and bar 67 (U). What remains for the performer to decide is whether an inverted mordent is preferable in all cases or whether the inverted shape of the motive (see e.g. L: bars 3/4) might not be more convincing if the ornament is also inverted (an "inverted" inverted mordent being, of course, a simple mordent).

The design of this "prelude in the character of a gigue" thus reveals itself as a remote relative of sonata form. This becomes particularly obvious when one combines structural observations derived from the distribution of the motives with those based on the main harmonic steps in the piece.

The rhythmic pattern within the subject consists exclusively of eighth-notes. Throughout the fugue, these are joined by quarter-notes and occasional longer note values, but the overall effect remains one of simplicity.

An analysis of the pitch pattern reveals that the first subphrase and its varied sequence are based on broken chord patterns (see e.g. B^b-F-D in bars 1/2, with B^b ornamented by a written-out turn). The third subphrase and its sequence, on the other hand, are composed as three-note descents linked by anticipations on the preceding weak eighth-notes. This observation is particularly interesting as it reveals an underlying structural rhythm behind the obvious uniformity of eighth-notes; to bring this out might be a special challenge for the performer (ex. 33):

The dynamic outline follows the dance-like design: the first two subphrases increase slightly, while the next two provide the corresponding relaxation.

Apart from an interval adjustment in the answer (which occurs only once in the piece; see bar 5 beat 3), the subject remains unchanged and uninverted. Only the final statement contains harmonic variation in that it commences and closes in F major (see bars 78/79 and 81/82) but touches the minor mode (see the Ab) in-between.

The sketch shows the subject in its manifold quasi-polyphonic surroundings. Although the two groups of counter-subjects never occur simultaneously as presented here, it is interesting to view them as parts of a single, almost homophonically designed pattern. Dynamic independence is only gained by CS3 and - theoretically though not perceptibly - by cs1 (ex. 35):

Taking into consideration the material exposed in these episodes as well as the harmonic closes incorporated in them, one can further distinguish a number of sub-divisions:

Material from the subject and the counter-subjects is prominently present in the episodes. If, for easier reference, one calls the subject's first subphrase with its ornamented broken chord "a" and the third one with the slurred pairs "b", then the following design can be made evident:

The structural correspondence of E3b and E9c, with or without that of E3a and E9b, is an important factor in the design of the fugue.

Section I encompasses the two initial statements, a bridging episode (E1) and the third entry followed by a cadential close in the home key (E2a). The second half of the same episode then represents a "change of mind" in that it undertakes a new start with a modulation and thus prepares for a redundant statement. Thereafter, a slightly longer episode with two dynamically decreasing segments (E3) completes this section with a strong cadential close in the dominant key F major. With regard to material, this section is unified by the exclusive appearance of cs1 and cs2 as companions to the subject.

The beginning of section II is marked by the simultaneous introduction of the two counter-subjects CS3 and CS4 which stay with the subject thereafter. The section contains three subject statements, linked by short episodes and completed by a passage which takes up the first, aborted cadential close of the fugue (compare E6 with E2a), concluding here in E^b major, the subdominant key of the fugue. The fact that this cadence remains unresolved in the middle voice ties the second and third sections together. This impression is reinforced by the use of the same contrapuntal material for both sections, in contrast to the first section.

The third section consists of three statements separated by long episodes. The observation that the third statement is redundant (it repeats an upper-voice entry), together with the recognition of a "false" lower-voice entry in the preceding episode (E8), leads to the assumption that section III is built along the same lines as section I, i.e. as a disguised recapitulation.

The table below shows the entries and their keys. For a sketch showing the entire design of the fugue in B^b major see ex. 36.

This is a playful fugue in which powerful build-ups of tension are not the issue. The alternation of subject statements and slightly lighter episodes determine most dynamic processes. Additional developments are created by the dynamic gesture of each episode and by the change of mode in the subject statements.

Within the first section, the tension rises from a graceful but not too subdued beginning through three subject statements and a bridging episode. It subsides during the cadential close of E2a, only to be picked up immediately and brought to a first climax in the redundant lower-voice entry which, owing to its pitch position a fourth below the previous one, gives the (deceiving) impression of a fourth-voice entry. The seven-bar long E3 provides a gradual relaxation.

Section II begins, despite its one-bar long rests in the upper and lower voices, in a more assertive color as the subject is now enhanced by the slightly more independent new counter-subjects. Despite a dynamically diminishing episode, the second entry maintains the elevated tension, mainly because of its very exposed pitch position in the highest register of the Baroque keyboard. The next episode with its increase then provides a powerful preparation to the first minor-mode statement in this fugue which, due to the particular character of the subject, is for once much heavier and more powerful than the original in the major mode. The tension then subsides in the final episode of this section.