Clarinet Concerto (Mozart)

Mozart's Clarinet Concerto in A major, K. 622, was written in October 1791 for the clarinetist Anton Stadler. It consists of three movements, in a fast–slow–fast succession:
History.
As there is no autograph for this concerto and as it was published posthumously, it is difficult to understand all of Mozart's intentions. The only relic of this concerto written in Mozart's hand is an excerpt of an earlier rendition of the concerto written for basset horn in G (K. 584b/621b). This excerpt is nearly identical to the corresponding section in the published version for A clarinet.
Mozart originally intended the piece to be written for basset horn, as Anton Stadler was also a virtuoso basset horn player, but eventually was convinced the piece would be more effective for clarinet. However, several notes throughout the piece go beyond the conventional range of the A clarinet; Mozart may have intended the piece to be played on the basset clarinet, a special clarinet championed by Stadler that had a range down to low (written) C, instead of stopping at (written) E as standard clarinets do.
Even in Mozart's day, the basset clarinet was a rare, custom-made instrument, so when the piece was published posthumously, a new version was arranged with the low notes transposed to regular range. This has proven a problematic decision, as the autograph no longer exists, having been pawned by Stadler, and until the mid 20th century musicologists did not know that the only version of the concerto written by Mozart's hand had not been heard since Stadler's lifetime. Attempts were made to reconstruct the original version, and new basset clarinets have been built for the specific purpose of performing Mozart's concerto and clarinet quintet.
Music.
The modern scoring of the work is for solo clarinet in A, two flutes, two bassoons, two horns (in A and D, often transcribed for horns in F), and strings.
I. Allegro.
The concerto opens with a sonata-form movement in A major. The form of the movement is as follows:
The first theme begins an orchestral "ritornello" that is joyful and light:
\new Score {
 \new Staff = "clarinet" {
 \transpose c a
 \relative c" {
 \set Staff.midiInstrument = #"clarinet"
 \clef treble
 \key c \major
 \time 4/4
 \tempo "Allegro"
 \set Score.tempoHideNote = ##t
 \tempo 4 = 120
 g2\p e4.( f8) | a8( g) f-. e-. e4 r | 
 f4( d8) r f4( d8) r | c2( b8) r r4
</score>
It soon transforms into a flurry of sixteenth notes in descending sequence, played by the violins and flutes while the lower instruments drive the piece forward. After the medial caesura, the strings begin a series of canons before the first closing theme, featuring first and second violins, enters. The second closing theme is much more subtle until the fanfare of its final two bars. As the soloist enters, the clarinet repeats the opening theme with the expected added ornamentation. As the orchestra restates the main theme, the clarinet traverses the whole range of the instrument with several flourishes.
The secondary theme begins in the parallel minor, and eventually tonicizes C major before arriving in the dominant key, E major. At the end of the E-major section, there is a short pause, where the soloist conventionally improvises a short "eingang" (cadenza), although no context is offered for a true cadenza. The canonic material of the opening ritornello returns, this time involving the clarinet and leads to the novel feature of the soloist accompanying the orchestra with an Alberti bass over the first closing theme. The orchestral ritornello returns, ending with the second closing theme.
The development section explores a few new key areas including F minor and D major, and even has some hints of the Baroque. Before the formal orchestral "ritornello" leading into the recapitulation, Mozart writes a series of descending sequences with the cellos and bassoons holding suspensions over staccato strings.
As is conventional in Classical concerto form, in the recapitulation the soloist and orchestra are united, and the secondary theme is altered to stay in the tonic. As the secondary theme comes to a close, the clarinet has another chance to improvise briefly, and this time leads the canonic material that follows. The Alberti bass and arpeggios over diminished chords for the soloist recur before the movement ends in a cheerful final orchestral "ritornello".
The solo exposition of this movement appears in almost every professional orchestral clarinet audition.
II. Adagio.
The second movement, which is in rounded binary form (i.e. ABA'), is in D major. It opens with the soloist playing the movement's primary theme with orchestral repetition:
\new Score {
 \new Staff = "clarinet" {
 \transpose c a
 \relative c' {
 \set Staff.midiInstrument = #"clarinet"
 \clef treble
 \key f \major
 \time 3/4
 \tempo "Adagio"
 \set Score.tempoHideNote = ##t
 \tempo 4 = 60
 c4( f4. a8) | a8( g) f4 r | c4.( f8 a c) | c8( bes) a4 r |
</score>
The B section, in which the solo part is always prominent, exploits both the chalumeau and clarion registers. The only true cadenza of the entire work occurs right at the end of the B section, immediately before the return of the A section. There are some passages that exploit the lowest notes of the basset clarinet in the B section.
III. Rondo: Allegro.
The concerto ends with a movement in A major. This movement is a blend of sonata and rondo forms that Mozart developed in his piano concertos, most notably the A major Piano Concerto, K. 488. It is in ABACABA form, with the middle A's being shorter restatements of the theme, unlike regular rondo form which is ABACA.
The movement opens with a cheerful theme:
\new Score {
 \new Staff = "clarinet" {
 \transpose c a
 \relative c' {
 \set Staff.midiInstrument = #"clarinet"
 \clef treble
 \key c \major
 \time 6/8
 \tempo "Allegro"
 \set Score.tempoHideNote = ##t
 \tempo 8 = 240
 \partial 16*2 e16( f) | g8-. g-. g-. a16( g fis g a g) |
 f!4.( e8) r c'16( b) | a8-. a-. a16( g) f8-. f16( e d c) |
 b8-.( c-. cis-.) d r
</score>
This refrain is interspersed with episodes either echoing this mood or recalling the darker colours of the first movement:
Reception.
Stadler played the concerto at its premiere in Prague on October 16, 1791, and his performance was favorably received. Without mentioning Mozart's work, the "Berlin Musikalisches Wochenblatt" noted in January 1792, "Herr Stadeler, a clarinettist from Vienna. A man of great talent and recognised as such at court... His playing is brilliant and bears witness to his assurance." There was some disagreement on the value of Stadler's extension; some even faulted Mozart for writing for the extended instrument.
In recent years, the restored original version has been recorded by many artists.