Subject

The double subject presents several motifs that will develop throughout the fugue.

• The two voices of the double subject appear in red (upper) and blue (lower).
• The lower voice of the subject is derived from the motives of the upper voice.
• Bar 1: motif a.
• Bars 2 to 4: motif b in the upper voice, motif a_i (a transformed by inversion) in the lower voice.
• Bars 4 to 5: the subject concludes with the motif c in the upper voice and the motif a_ia (first notes of a_i transformed by augmentation) in the lower voice.

This image illustrates the motifs and variations that will appear throughout the fugue (the number indicates the measure):

Bars 5 to 7

These bars prepare the entrance of the answer:

• Motifs c and a_i in the lower voice.
• New motives c_a (c transformed by augmentation) and a_id (a_i transformed by diminution) in the upper voice.
• We modulate to G minor for the presentation of the answer.

Answer

The answer appears in the dominant key accompanied by the bass using some of the motifs already presented:

Bars 11 to 17

A longer section brings us back to C minor:

This passage is an example of the good use of harmonic ambiguity. We suggest a simplification that takes us through five keys.

• The keys follow a pattern of fifths: G Minor - C Minor - F Minor - B Flat Major - Eb Major - C Minor.
• Bach avoids clear modulations and tonal assertion.
• Delays, appoggiaturas, and syncopations accentuate the ambiguity.

Second exposition, subject

The subject reappears. We could think that this is a third entry, but after such a long passage as that from bars 11 to 17, we prefer to see this entry of the subject as a second exposition. The subject's voices appear inverted by an octave (now the red is lower than the blue). The upper voice acts as a counterpoint to the subject:

Second exposition, answer

Bars 21 and 22 use motifs c₂, a and a_i to prepare the entry of the answer (bar 23):

Episode

Bars 27 to 42 present a long episode based on some of the motifs already discussed.

Final presentation of the subject

Two false entries in bars 42 and 43 prepare the presentation in C minor of the subject (bar 44) with which we end this first section. The notes in red in bar 45 should be an octave lower as well as the blue notes in bar 46:

Section B develops the thematic material freely and does not follow the contrapuntal structure of a fugue.

Bars 49 to 53

A phrase based on variants of motifs c₂ and a_id takes us from C minor to G minor via E flat major:

Bars 53 to 59

On reaching G minor, the subject reappears (blue and red notes) using the variant b₂ in the lower voice:

Bars 59 to 67

From G minor, we modulate to F minor. We find the motifs a_i, a, b_i, a_id and variants of c₂:

Bars 67 to 83

• We start in F minor. We move through B flat major and E flat major to arrive in bar 75 in C minor where the subject reappears over its dominant using the new variant a_i2 in its lower voice.
• The subject takes us through F minor and the section concludes over the dominant of G minor.

Bars 83 to 93

We start on the dominant of G minor, modulate to C minor and end on its dominant.

Motives:

Bars 93 to 109

• We start on the C minor dominant.
• Pedal of F in bar 96, suggesting the key of F minor and even B minor, but we maintain the key of C minor.
• Last presentation of the subject on the C minor dominant in bar 105 using variant b₂ in the lower voice.
• Section B ends.

Motives: