Toccata and Fugue in F major, BWV 540

The Toccata and Fugue in F Major, BWV 540, is an organ work written by Johann Sebastian Bach, potentially dating from the composer's time in Weimar or in Leipzig. 
History.
No firm date can be established for the composition, and it has even been conjectured that the 2 parts were composed separately, with the toccata being a potentially more mature piece. Williams however describes that the differing "Affekt" of the two parts does not pose any problem to the hypothesis that the whole work was composed at the same period. This conception of "complementary movements" was even a favourite of Bach's, and the dramatic nature of the toccata as contrasted to the masterful counterpoint of the fugue should "not be misunderstood as mere discrepancy". Because of the range of the pedal parts, the toccata may have been written for a performance, around 1713, at the Weißenfels organ, with its pedal going up to f'.
Music.
Toccata.
<score %vorbis="1"%%T257066%> 
« « 
\new Staff { \clef treble \key f \major \tempo 8=120 \set Staff.midiInstrument = "flute" {
 \set Score.tempoHideNote = ##t
 \override Score.BarNumber #'transparent = ##t 
 \time 3/8
 \relative c'
\new Staff { \clef bass \key f \major \set Staff.midiInstrument = "flute" {
 \relative c
\new Staff { \clef bass \key f \major \set Staff.midiInstrument = "flute" {
 \relative c,
</score>
The toccata starts with a large linear canon (first 6 bars shown above) over a pedal point in F major. It is then followed by a pedal solo based upon material from the canon. The canon is reiterated with some variations in the dominant in C major. This time the hands are switched, and the left hand leads the right. This is again followed by a long pedal solo. The two large canon flourishes cover 108 measures of the composition. The pedal solos cover 60 measures. The concerto movement exhibits a seven-part structure. The canons and pedal solos effect the departure from the home key of F to the dominant C, and the entire rest of the movement, with its "concertante" 3-part imitation and striking "proto-waltzes", constitute the harmonic return. This formal pattern is unique within Bach's "œuvre".
Hermann Keller expresses his rapture as follows: " At the beginning the extensive linear construction of the two voices in canon, the proud calmness of the solos in the pedal, the piercing chord strokes, the fiery upswing of the second subject, the bold modulatory shifts, the inwardness of the three minor movements, the splendour of the end with the famous third inversion of the seventh chord, who would not be enthralled by that?"
The Toccata (as a prelude) is proportionally the largest of all Bach's works in the format of prelude-fugue. It is often treated as a show piece, with the ensuing fugue omitted. The Toccata's rhythmic signature suggests a "passepied" or a "musette", although the monumental scale of the movement does not support these characterizations. 
Nor does the harmonic adventurousness: 45 measures after the second pedal solo there is a dominant chord which resolves deceptively to the third-inversion secondary dominant of the neapolitan chord. In particular, the doubled root is found to move outward in contrary chromatic motion to a major 9th; in the bass by a descending half tone, which "absolutely" could not be farther from the expected fifth. Bach implements this powerful deceptive cadence three times in the piece; it would not become idiomatic until Chopin and Tchaikovsky.
Fugue.
<score %vorbis="1"%%T257066%> 
« « 
\new Staff { \clef treble \key f \major \tempo 4=120 \set Staff.midiInstrument = "flute" {
 \set Score.tempoHideNote = ##t
 \override Score.BarNumber #'transparent = ##t 
 \time 2/2
 \relative c
 « { r1 | r | r | r | r | %5
 r | r | r | r | r | %10
 r | f'1 | e2 es | d bes'~ | bes a | %15
 g1 | f | e4 } \\ { r1 | r | r | r | r | %5
 c1 | b2 bes | a f'~ | f e | d1 | %10
 c1~ | c4 b8 c d2~ | d4 g,8 f g4 a | bes c d e! | f c f2~ | %15
 f e2~ | e d2~ | d } »
\new Staff { \clef bass \key f \major \set Staff.midiInstrument = "flute" {
 \relative c
 { f1 | e2 es | d bes'~ | bes a | g1 | %5
 f4 g a2~ | a4 d,8 c d4 e | f g a b | c g c2~ | c bes~ | %10
 bes4 a8 g a4 f | d g,2 a8 b | c2. c4 | g'2. f8 e | d4 e f a, | %15
 bes g c bes | a a' b g | c
» »
</score>
The first subject (entries in the tenor, alto and soprano voices shown above) of the fugue is chromatic and ornamental. The second subject has a lot of modulation shifts and is sometimes initially presented as the counter-subject of the first. The Fugue is Bach's only thorough-going double fugue, where two subjects are exposed in separate sections and then combined. The effect is enhanced by the increasing rhythmic activity of the second subject and by the more frequent use of modulation in the final section of the fugue.
The bravura of the F-Major toccata, with its pedal solos and manual virtuosity, contrasts sharply with the rather sober opening of the Fugue. Both represent two diverse aspects of Italian influence: the motoric rhythms and sequential passagework of the Toccata, and the traditional alla breve counterpoint of the Fugue, with its chromaticism, harmonic suspensions, and uninterrupted succession of subjects and answers. These techniques are very similar to those used in the "Dorian" Toccata and Fugue in D minor, BWV 538.