Ernst Kurth devotes a section of his 1917 treatise "Grundlagen des linearen Kontrapunkts" to J. S. Bach's melodic style; one of his focuses therein is on a “balance of motions” that may characterize either a theme itself or a theme and its subsequent Fortspinnung together. This balance resides most obviously in contour, involving “the spaces as well as the directions of motions” (220); but it also significantly concerns rhythm. The rhythmic aspect of this balance may consist in the relative durational values that constitute successive ascending and descending phases of motion, or it may lie more removed from the musical surface, in the “waves” through which these successive ascents and descents proceed, whose crests relate to one another not only through linear pitch connections but also through the durations that separate them. Example 1 gives some fugue subjects whose balance arises from aspects of contour and surface rhythm; Example 2 gives a passage whose balance obtains between faster ascending and slower descending wave-shapes. 

After I compare Kurth's treatment of rhythm in this context to more recent Schenkerian work on Baroque phrase rhythm and suggest ways in which the two perspectives might be combined, I turn to a curious statement from Kurth, that downward-tending series of crests tend to move faster than upward-tending series (as they do in Example 2) (227). Although this statement is untenable in light of all the genres in which Bach composed, I argue that, nevertheless, consideration of the rhythmic relationships between upward and downward series of crests can be extremely revealing of a passage's energetics—whether an energetic balance emerges through continuous flux (as in the scenarios Kurth focuses on), or whether (potential) energy mounts steadily prior to a delayed balancing countermotion.

The opening ritornello from Bach's aria “Seht, seht! wie reißt, wie bricht, wie fällt” (BWV 92), analyzed in Example 3, describes the latter scenario. In this example, a Schenkerian graph appears beneath a staff that gives the ritornello's main melody; a stylized contour line marks wave crests with loops and varies in thickness to approximate the degree of tonal “effort” the melody implies (or, perhaps, the energy it imparts to its tonal environment). In the double-waves of the first two measures, ascending runs coordinate with reaching-over figures to stretch out the chordal boundaries of the ritornello's initial tonic and move through III and IV Stufen before activating the dominant in measure 5. In measures 3–5, double waves become triple and then quadruple, while middleground motion slows: it is as if more resistance is encountered, and more effort is required, to push the upper line beyond the Kopfton. The final stages of this effort even counteract the first motions of the Urlinie as they strive for scale degree 8. It is only in measure 6 that this ascending energization finds balance in a wide-ranging descent that courses freely athwart the piece's obligatory register before joining the final cadence.

Further examples will represent the genres of dance suite, cantata aria, and concerto.