A recent Skyped piano lesson to London, England, brought home the ins and outs of teaching Bach's 2-part Invention in C Major, BWV 772.
Across a vast ocean, my student and I unraveled the genius of Johann Sebastian by examining his SUBJECT theme, and how he put it (and bits of it) through a series of clever manipulations. (Evelyn Glennie, world class percussionist, asserts that what we don't SEE in the score, whether it be associated with Bach, Mozart, et al, is what we must NOT ignore)
Yet, having an eyeful of Bach's two-page composition, can yield a treasure trove of insights that make a throw fate to the wind, inspirational, idealized performance a reality. No one can really wing it, without an adequate cognitive, affective, and physical foundation.
Invention 1 packs so much into so little. That is, the economy of two pages, does not bar the composition's complexity.
Some words to throw around: Counterpoint, or independent voices interacting; Imitation, self-explanatory; Inversion (playing the subject, or pieces of it, backwards, or inverted) Augmentation: lengthening the subject's note values, or just a portion of it--likewise, inverting it.
Sequences: the same melodic or bass idea, played up a step, skip, whatever--or down, with a certain symmetry.
Modulations: transitions to different keys.
The above are explored in the video attached, making learning Bach over Skype as deeply probing and meaningful as having the pupil LIVE and in living color.
Finally, here's a snatch of a more complex form of the composer's counterpoint, covered in a recent blog revisit: the FUGUE, BWV 847 in C minor (my updated reading)