|A portrait which may show Bach in 1750 (Photo credit: Wikipedia)|
The Toccata leaves the impression of a chase between voices and begins with a prolonged and playful two-voice canon over a long tonic pedal point (Idea A). After this canon, Bach writes another virtuosic episode - a pedal solo in the tonic key which leads to a cadence in the Dominant - C major. Now the voice parts switch places and the canon begins all over again, only this time in the Dominant key (C major). These two sections serve to establish both the Tonic and the Dominant keys and have a function, similar to the North German Passaggio in a Praeludium.
After this episode, the chase stops but all voices begin a long and tiring journey (for the performer, that is) through various related keys in descending and ascending sequences (Idea B based on arpeggio figure). Through the course of this Toccata, canonic idea A and sequential idea B alternate and create an intriguing structural balance. In developing the idea A, Bach evidently shows his mastery of a double and sometimes even triple invertible counterpoint at the interval of an octave. This basically is a technique allowing voice switching. It only works if the composer uses the suitable intervals (most of the time thirds and sixths, avoiding fifths which in inversion become a forbidden fourth). Suspensions of a second and seventh are welcomed in this technique, too.
Because of repeating two musical ideas, this Toccata shows the influence of the Italian Ritornello form. Bach learned to use this form in Weimar from transcribing for the keyboard the concertos of Vivaldi and his contemporaries.
The fugue, on the other hand, provides a welcomed relaxation for the organist from the technical point of view. However, Bach provides another challenge, e.g. old-fashioned "Palestrina" style fugue with alla breve meter (cut-time) in Style antico (the old style). This is a double fugue, which means that a composer has to develop two musical themes. Both of the themes must work in invertible counterpoint with each other. In the exposition and counter-exposition of the first theme, Bach develops the solemn, slow, and vocal musical idea in all four voices.
The second theme appears to be playful, dance-like, which reminds of a Baroque dance Gavotte. During this section, the pedal part remains silent and waits for its entrance until the powerful combination of both themes towards the close of a fugue. While listening to the fugue in this wonderful video, feel free to count the number of appearances of the first theme.