J S Bach's first two-part invention in C major is a keyboard work in which the music is "invented" by means of thematic transformations of a short, simple figure, called the subject, S. This subject is divided into two motives, a and b. The a motive consists of a rising 4-note scale beginning off the beat and ending on the next beat, a ubiquitous figure in Bach's music. The b motive, also 4-notes and rhythmically identical to a, turns with every note. A seemingly additional motive, c, is normally cadential. It is actually not entirely new but is derived from b by partial inversion and augmentation (It is also a 4-note figure, ending on a beat.); c is associated with a trill on the second note. (In measures 5 and 13 it contains an octave displacement of the first note.)
Virtually every note of this invention comes from the subject, as shown in the following score analysis. Only the formulaic cadences depart slightly. All the other material is derived by means of symmetrical operations on S or of a part. These operations consist of inversion, augmentation, and transposition. Elision (v) is used briefly in the final cadence.
The A section consists of 6 measures, rather than the 8 of the other two. Each of the three sections, A, B and C, is a binary, with the first being 2+4, and the other two being 4+4 each.
The following is a score analysis with symbols indicating the transformations of the basic subject. For a key to the meaning of these symbols, follow this link: Key to Suggestions for Formal Analysis. Play it:
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