Mozart first used the basset horn in the Serenade for Winds, K. 361/370a, composed in the spring of 1781. Shortly afterward, he employed the instrument in his first Vienna opera, Die Entführung aus dem Serail. He also used the basset horn to symbolize sadness in the Masonic Funeral Music, K. 477/479a.

The basset horn is much like an alto clarinet, but with a smaller bore, producing a different color. It is also slightly "whiney" in comparison to B flat or A clarinets. One of the champions of the basset horn in Mozart's time was Anton Paul Stadler (1753-1812), clarinetist and great friend of the composer. For Stadler, Mozart wrote the Clarinet Quintet, K. 581, in September 1789 and the Clarinet Concerto, K. 622, in October 1791.

It is very likely that Stadler, accompanied by two other players, read through Mozarts Divertimentos, K. Anh. 229, for their own amusement at Mozart's home. During these evening sessions, the musicians tried different instruments, evidently deciding on the three basset horns as the best instrumentation. Mozart's willingness to experiment with timbre justifies the editions of the five divertimentos in a setting for two basset horns or clarinets with bassoon.

All five divertimentos are in B flat major; only a few movements are in other keys. All are in three movements and the first three begin with an Allegro, which is followed by a minuet and trio, a slow movement, another minuet and trio, and a closing Rondo in Allegro tempo. The fourth Divertimento also opens and closes with fast movements but these enclose two slow movements and a central minuet and trio. The last Divertimento diverges furthest from the norm, beginning with an Adagio followed by a minuet and trio, another Adagio, a Polonaise, and a Romanze.

The first movements of Nos. 1, 3, and 4 are in sonata form with cursory development sections; Nos. 2 and 5 begin with movements in rounded binary form. The minuet and trio movements are formally traditional with some melodic variation, while the trios are some of the only sections in keys other than B flat.

In the slow movements, we find the most interesting, lyrical writing, especially in the Larghetto of No. 2. In this movement, the three instruments possess equal levels of melodic importance, with the bassoon occasionally venturing into the range of the clarinets. Pulsating chromatic lines produce a strong sense of melancholy, regardless of the instrumentation. The central Adagio of No. 3 is of a different texture, in which the first clarinet is the primary instrument, the other two instruments subordinate to its alternately sustaining and fleeting melody.

Most unusual is the fifth of the set. Not only does it begin with an Adagio but the typical second Minuet is replaced by a polonaise. The polonaise is a Polish couple dance that by the eighteenth century became an instrumental work with the following characteristics: triple meter, moderate tempo, lack of upbeats, and repetition of rhythmic figures. All of these features appear in Mozart's polonaise, set in the subdominant (E flat major). Accents on the second half of beats are common and a rhythmic figure consisting of an eighth note followed by two sixteenth notes appears numerous times. The movement is rounded binary, with four measures of new material in the second part preceding a partial return to the first theme. The closing Romanze is also binary, but for the new material in the second half, Mozart fragments and stretches portions of the first theme in a manner we find in his more serious works.

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Divertimento in Bb, K.Anh.229, No.2

As the headnote indicates, there is some doubt about the precise year of composition of this Divertimento, as well as the other four making up K. 439. Moreover, their authorship has been challenged by some musicologists, though they still appear to be the work of Mozart. This Divertimento in B flat major, like its other four siblings in the set, is cast in five movements, the second and fourth of which are charming Minuets. The opening panel is a lively but very brief Allegro, whose playful manner is brilliantly conveyed in the imaginative upper-register writing for the two lead basset horns. The ensuing four-minute Minuet is nearly four times longer. It is graceful in its unhurried manner and its trio section is lyrical and equally elegant. The central movement (Larghetto) is dreamy but somewhat playful in its laggardly manner, contrasting well with the livelier Minuets that surround it. The second Minuet is busier and a bit more colorful than the first one in its outer sections. Its trio features a mellow theme whose stop-and-start manner imparts an almost sassy sense of self-confidence. The finale is a Rondo brimming with energy and playfulness. Its main theme bears a strong resemblance to a secondary theme in the first movement of the Mozart Piano Concerto No. 21. An attractive, brief cadenza near the close leads to a colorful conclusion.

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Divertimento in Bb, K.Anh.229, No.3

The date(s) of this and four companion Divertimenti, originally written for three basset horns, is (are) conjectural. The nearest scholars can estimate is "?1781-2, or c. 1785" (The Mozart Compendium, 1990), "1783 or later" (The Compleat Mozart, also 1990), and "?1783 or later" (The New Grove Mozart, 1984).

All were unknown until 1800, when Mozart's widow Constanze wrote to a publisher that clarinetist "Anton Stadler still had in his possession copies of trios by Mozart for basset horns." In 1803, Breitkopf & Härtel published "some pieces for two basset horns and bassoon(!) . . . under Mozart's name. In a later issue (by Simrock of Bonn), 25 pieces were . . . divided into five 'Serenades' of five pieces each [for] two clarinets and bassoon. All later editions and arrangements were based on this Simrock issue."

The basset horn was an alto clarinet, so to speak, with right angles and an extended bass range, subsequently replaced by grandparents of the modern instrument. Mozart most probably created these pieces for the pleasure of Stadler, his brother, and a third player. They've been recorded in that form by the Trio di Clarone on a pricey EMI CD. The signature key throughout is B flat major. Only Divertimento No. 4 departs slightly from a pattern of Allegro, Menuetto e Trio, slow movement, second Menuetto, and rondo-finale.

In Divertimento No. 3, played in an arrangement for flute, clarinet and bassoon, the third movement is an Adagio whose mellifluous clarinet arpeggios anticipate the third-movement trio in Symphony No. 39. The second minuet has subject matter shared by a bouncy finale, published as "(Allegro assai)." Good guess.

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Divertimento in Bb, K.Anh.229, No.4

This is the penultimate of the five Divertimentos making up the K. 439 set, a group of works whose authorship some scholars question. But thematic similarities in the Rondo finale of the Divertimento No. 2 with the first movement of the composer's Piano Concerto No. 21, and in this Divertimento's fourth movement (Adagio) with The Magic Flute's "March of the Priests," would suggest Mozart is likely the composer. Moreover, the first-movement main theme here also alludes to its glorious counterpart in the finale of Mozart's Symphony No. 41. Unlike the other four works in the K. 439 set, which feature a single central slow movement, two of this Divertimento in B flat major's five panels are slow: the Larghetto second and Adagio fourth. The Allegro first movement is lively and colorful, and while it might suggest echoes of the later symphony, its manner is lighter and far less serious. The ensuing Larghetto has an almost gossamer character in the mellow lightheartedness of its main theme. The third-movement Minuet is bright but more playful than elegant in its outer sections, while its trio is serene and at times dreamy. Dreamy is the chief characteristic of the lovely Adagio fourth movement, which actually sounds slower than the Larghetto. The concluding Allegretto is chipper in the energetic chirping and cackles of the main theme, and no less joyous and bright in the playful but comparatively mellow alternate material.

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