In Kinsky and Halm's list of Beethoven's work, published in 1955, the three Duos for clarinet and bassoon, WoO 27, are accepted as authentic; however, later research suggests that they are spurious. Elliot Forbes, in his edition of Thayer's Life of Beethoven, suggests the Duos were composed in Bonn, as prominent players of these instrument were part of the ensemble used for dinner music at the electoral court. Establishing their publication history has also proved difficult, and scholars know only that they were printed in Paris sometime between 1810 and 1815. There is no record of any comment by Beethoven on the pieces.
The first of the three duets, in C major, opens with an Allegro commodo in 4/4 meter. In sonata form, the movement's first and second themes are in the clarinet part, the transitional material, creating a modulation to the dominant, in the bassoon. A brief return of the second theme closes the exposition. The short development section is built upon new figures, including a dotted motive that anticipates the Rondo finale, and the recapitulation skips a large transitional segment of the exposition. The direction to repeat both the development and recapitulation is an early Classical-era characteristic. The central Larghetto is in C minor and serves as a slow introduction to the ensuing Rondo finale, in C major. Most notable is the sudden shift to a murky C minor for the movement's second episode.
The Duo in F major (№2) opens with an Allegro affettuoso in 4/4 meter. In sonata form, the movement modulates to the dominant, C major. After a brief development, focusing on the opening bassoon line, the recapitulation follows the pattern established by the C major Duo, in which a large section of the exposition is abandoned and the second theme is almost immediately performed in the tonic, as is the ensuing closing material. Passages from the exposition are varied in interesting ways before the movement ends and the composer calls for a repeat of both the development and recapitulation, an early Classical-era characteristic. The central "Aria," marked Larghetto and in the relative minor (D minor), is built of two eight-measure phrases, each repeated. Although quite elegant, the Aria functions less as a fully fledged movement than as a introduction to the finale, a Rondo in C major. Suggestions of G major and A minor mark the Rondo's lengthy episode.
(John Palmer, Rovi, answers.com)