A prolific period during the summer of 1788 brought to life the three final symphonies of Mozart, which represent the apex of Viennese Classicism and Mozart's symphonic writing. These symphonies show all the refinement, craftsmanship, and motivic construction that distinguishes this style, plus Mozart's expressive chromaticism, drama and lyricism. Notable in the Symphony No. 39 is a motivic construction that unifies not just individual movements, but the entire symphony, a concept that is quite new. These motives are used as building blocks, from which the principal musical materials are constructed. There are five main motives: a) the melodic arpeggio, b) the melodic descending scalar passage of three to five notes, c) a rapid descending scale, d) dotted rhythms, and e) the interval of a sixth. An additional quality worth noting is the increased use of chromaticism, which lends an heightened expressiveness to the work.
Only a handful of Mozart's symphonies begin with a slow introduction, an element more commonly found in the symphonies of Haydn, and the 39th is the only one of the final three symphonies to begin this way. This slow introduction is a direct descendant of the French Overture, which features dotted rhythms and rapid descending scale passages (motives c and d). The unyielding dissonances heard here have more the flavor of the High Baroque than Viennese Classicism. This dramatic introduction gives way to a relaxed and lyrical first theme. The motives in this theme are the melodic arpeggio (a), descending melodic scalar passage (b), and the interval of a sixth. Note also the immediate development of the first theme, not waiting for the development proper, foreshadowing Beethoven's methods. In fact, the first theme is not heard at all in the development: it is entirely developed in the exposition and recapitulation.
The energy level picks up dramatically at the bridge passage which serves to modulate to the dominant key. The rapid scales of the introduction are again heard, and we realize that the introduction is also thematically related to the body of the movement. The second theme group follows, featuring the descending melodic lines from motive b. The meandering eighth-notes in the violins outline this descending figure, and the woodwinds a few bars later confirm that this was a decoration of the motive. The closing theme re-introduces the dotted figures from the introduction. After an exposition repeat, Mozart surprises us with a rapid modulation to start the development. The typical fifth-relations of the Classical period are here replaced with a modulation by descending thirds. B-flat major is immediately followed by its relative minor, g, then E-flat dominant seven, resolving into A-flat. The concise development section features the second, bridge, and closing themes, before sliding into the recapitulation.
The second movement, in Sonatina form, is also built from the five basic motives. The first theme is an inversion of the melodic descending figure, with dotted rhythm; the stormy bridge passage features the melodic arpeggio and rapid descending scales; and the beautiful closing theme, with contrapuntal woodwinds over sustained strings, is a wonderful moment. In the place of a development, there is a brief retransition that brings back the first theme, now embellished with a countermelody. After a few aborted attempts to finish the movement, during which Mozart slides into a deceptive cadence not once, but twice, the music relaxes into the final cadence.
The warm and lively minuet that follows is full of charm and buoyancy. Here, too, is the presence of the building-block motives. Most prominent in the minuet are the descending melodic lines, particularly at the cadences. The trio features a variant of the main theme of the first movement. The fiery and energetic finale is a monothematic sonata-allegro movement, which is a melding of four of the motives: the melodic arpeggio, the melodic descending passage, the rapid descending scale, and the interval of a sixth. The main theme is an embellished melodic arpeggio which, because of the tempo, has both the melodic and the rapid descending scale in one. The interval of a sixth is now filled in by the rapid scales. The second and closing themes are variants of the main theme, but they each contain the head motive of the filled-in arpeggio. The tongue-in-cheek ending is pure Mozart, where the head motive is played twice, ending on the weak beat. One can almost hear Mozart chuckling after the last note has sounded.