Binary Form

A [a (measures 1-4) + a (measures 5-8)]

B [b (measures 9-14) + a1 (measures 15-18)]

In binary form, placing the 'a' section at the conclusion of the latter B section is often observed in binary forms from the Classical period onwards. The re-presentation of the 'a' section at the conclusion provides a sense of unity.

A characteristic structural pattern of the Baroque era is the enlargement of the middle section by placing a transitional section immediately before the re-presentation of the theme. Similarly, in Bach's Inventions, a transitional section with repetitive progressions, such as sequences, is placed immediately before the theme is re-presented in the concluding part. While some interpret this as an independent "part," its role is functionally similar to a transition in sonata form. Therefore, the author is somewhat hesitant to consider it a separate "part." It is more rational to view it as a connecting section from the middle section to the concluding part, or rather, as part of the middle section.

However, considering this, the structure of the 'b' section is, if anything, closer to the first exposition in an Invention (e.g., Invention No. 1) than to the middle section (second exposition). Specifically, after the presentation of a new theme in measures 9-10, the theme is developed through sequence in measures 11-12, followed by a temporary cadence (half cadence) in measures 13-14. This flow is similar to the first exposition found in Invention No. 1.

Compared to the A section, where 'a' is fully repeated, the B section, though brief, forms a flow of presentation → development → cadence, which suggests it might have become enlarged.

Throughout the piece, frequent imitation between the upper and lower voices is not observed, and while the lower voice does not strongly convey a melodic element, the upper and lower voices are often in an unequal duration relationship (i.e., when one has a long note value, the other has a short one). From this, it can be felt that the relationship is not one of pure melody and accompaniment, but rather that the lower voice also exhibits quasi-melodic movement.

The piece is in binary form.

• A [a (measures 1-4) + a (measures 5-8)]
• B [b (measures 9-14) + a1 (measures 15-18)]

Characteristics of the Theme

The theme spans measures 1 to 4. It is bipartite, with the main melody beginning with a leap of a fifth upwards, ascending in the first half, and then leaping a fourth downwards and descending in the second half. A characteristic motif in the first half is the figure e-h-h, consisting of two quarter notes and one half note (after leaping a fifth from E to H, the H is repeated as a half note). In the second half, the motion descends a fourth from E to H, and this movement is repeated in quarter notes.

These two motifs are also used in the b section, albeit slightly altered. For instance, the main melody in the right hand at measure 9 uses the motif from measure 1, and the descending fourth motif is used within a sequence from measures 11 to 13.

It is precisely because of the development of these motifs that even if a seemingly completely different melody appears, it does not feel out of place.

As a characteristic of the theme as a whole, the inclusion of many leaps suggests a light and rhythmic expression.

On Structure

The theme concludes with an imperfect cadence in the A section and a perfect cadence in the B section.

While generally structured in four-measure phrases, only the b section (measures 9 to 14) is extended to six measures. This is due to the transitional sequence inserted between measures 11 and 12. In Bach's Inventions, it is common to use sequences to form transitional passages to return to the tonic key before the theme's recapitulation. The progression from measure 11 is considered to have a similar implication.

On Texture

Comparing the movements of the right and left hands, the left hand does not exhibit as many melodic elements as the right. Therefore, the right hand is generally considered to carry the main melody. On the other hand, the left hand is not merely an accompaniment; examining the two voices, they are often structured by contrary motion (where two voices move in opposite directions, e.g., one voice ascends while the other descends) and unequal counterpoint (where two voices proceed with different note values, e.g., one voice has a half note while the other has two quarter notes, resulting in a 1:2 unequal counterpoint).

Consequently, a more three-dimensional expression can be achieved by playing the left hand with a nuanced and conscious approach, treating it somewhat like a counter-melody to the main melody.