|Book 2 - No. 4 - C sharp minor - Fugue|
Perpetual motion. 12/16 allows a lot of water under the bridge between strong down beats, the essential pulse. 16th notes speed steadily by throughout the entire fugue. Some vote strongly for this being a double fugue. The other interpretations is that it is a single fugue with a very prominent countersubject. The countersubject enjoys what appears to be a fully independent exposition without the first subject (see the diagram). As such, it is "exposed" on its own, though it has already appeared first in the guise of a countersubject. It is a compelling moment. In this sense, it would make a very "organic" double fugue, that is, subtle and certainly non-conventional. Either way, both musical entities (subject and countersubject) enjoy a vivid and independent journey.
This fugue also features a high percentage of episode, rich counterpoint that is independent of either complete subject or countersubject. The music is running almost continuously in full three-voice texture, breathlessly busy, a buzz of intense conversation with seemingly so much to say. There are gestures, calls and responses, figures and counter-figures, a constant rush of dense eloquence punctuated by the recurrence of the familiar. What additional treasures lay hidden within? The mind reels but longs to grasp. The perpetual motion overwhelms in the most satisfying sense of the word.
In addition to inversion, augmentation and diminution, a musical motive such as a subject or countersubject can be presented in retrograde, also known as crab motion or cancrizans. Retrograde means backwards, just as in astronomy, the planets have an occasional apparent retrograde motion from our vantage point on earth. This is a rare musical transformation most often found in canon or invention. It is difficult to hear, but not hard to see in musical notation. There appears to be at least one occurrence of what can be considered a retrograde version of the countersubject in this fugue. Here is a quote from the fugue showing the countersubject in retrograde
And here it is, written backwards:
You can see that closely matches the countersubject: