Describe the structure of the central fugal section of the Ouverture of Bachs Orchestral Suite No. 3

A fugue by definition is a polyphonic structure based on a series of entries from a central theme, or subject. Each part in a fugue is called a ‘voice’ regardless of its vocal or instrumental properties thus fore meaning that a fugue may have 3, 4 or 5 voices. These voices present subject and answers, that are usually based around the tonic harmony (subject) and dominant harmony (answer). If an answer is an exact copy, it can be called a ‘real’ answer whereas one that has been altered can be called a ‘tonal’ answer. Once a voice has performed a subject, it will perform a counter subject in order to fit with the answer.

The fugal section of the Ouverture can be split into five distinct parts, these being the exposition, 1st episode, middle entries, 2nd episode and final entries. Once all voices have performed the first set of subject and answers the exposition is complete. However, there may be subsequent sets of entries in varying keys: the middle entries may be in the subdominant or dominant however the final set of entries will be in the tonic key of D major. In between sets of entries, there may be more freely structured sections (episodes) with material that may be based from the subject or countersubject.

The exposition is the first set of entries heard, from bars 24-41. Entries for the exposition are typically in descending order with violin 1, violin 2, viola and then finally the basso continuo part. This is equivalent in vocal music to SATB, and as instruments in a fugue are named as ‘voices’ this may not be a coincidence. Three different countersubjects are played during the exposition. The first countersubject appear at bar 253 with the 1st violin playing a melody very similar to the subject, but down a 5th. Countersubject 2 (also in the 1st violin) is played for the first time at bar 281 and consists of many semiquavers, some that move in step whereas others that move in leaps of up to a 5th. The third and final countersubject (again, played by violin 3 is a much simpler melodic tune, as it is mostly repeated quavers on D and E.  A final subject entry in the basso continuo at bar 38 is accompanied by countersubjects 1, 2 and 3 in the other three string parts.

The middle entries provide a tutti section, with the 1st and 2nd oboe still covering the 1st and 2nd violin parts respectively. In this section, the trumpets continue to play triadic material and the timpani provide pedal notes of D and A (still the tonic and dominant). 5 sections comprise the middle entries, and in each of these sections the fugal subject is played, along with some combination of countersubjects 1, 2 and 3. The subjects move between the continuo and the violin in the middle entries by way of sequence.

The final entries are a repeat of bars 24-41, although countersubjects 1, 2 and 3 play a full role from the start with violin 1 playing the subject, violin 2 the 1st countersubject, the viola the 2nd countersubject and the continuo the third countersubject. This again is an example of the SATB structure.