Upon first listening to this work, many conventional conceptions of rhythm come to mind: there is a steady eight-note pulse; the opening 12-measure unit is neatly divided into three 4-measure phrases (an easily identifiable hyper-meter); and the brief interruption of the eight-note pulse half-way through the work establishes a two-part structure (each part of which has a clear beginning and end). The start of the second part (m. 13) suggests periodicity, given that it is a re-beginning. And in this respect, one could interpret the form of this work—albeit very loosely—as a period or periodic hybrid.
Despite the snaking chromaticism in the left hand, the upper voice establishes a consistent accent pattern, which is emphasized by Chopin’s persistent use of upper-neighbor tones. This pattern, however, is obscured in the second part of the work, where Chopin deviates from the opening measures and launches into a stretto passage that sounds quasi-improvisatory.
The stretching of tempo asked for in this section, which is typical of Chopin’s rubato technique, raises an interesting question with regards to our perception of rhythm: are listeners able to follow an implied background pulse despite ongoing superficial contortions of tempo, or do they simply lose their orientation momentarily? The answer to this question depends partly on the performer. From a performative point of view, we are often taught to count internally in order to proportion variations in tempo. I.e., we are discouraged from playing gradual changes in tempo as we “feel” them; instead, we are encouraged to construct some kind of internal scaffolding such that the performance isn’t “random”.
One final point of interest: as the music progresses, the overall sense of rhythm seems to become weaker and weaker. The first twelve measures, as already noted, divide nicely into symmetrical units with a clear end point; the ensuing eleven measures, though still with a steady eighth-note pulse and recognizable accent structure, loosen our sense of rhythmic orientation via stretto; and the final two measures, which are set apart by a fermata, obscure this sense altogether.
The formulaic cadential tag that closes the work then reestablishes order, both rhythmically and harmonically. And so is seems that rhythm contributes significantly to our emotional response to the work: we are grounded, then lost, and then reunited with order. It would be fascinating to see what kinds of emotions this sort of pattern elicits in listeners.
In summary, it seems that this piece can be viewed fruitfully from at least three of the four rhythmic perspectives we talked about: rhythm as order and proportion, rhythm as movement, and rhythm as form.