Mozart completed the Piano Concerto in A Major, K. 488, in March 1786 and it is a graceful piece in three movements. It used a small orchestra with two flutes, two clarinets in A, two bassoons, and two horns in A, along with the usual string orchestra. The first movement embodies the form called a “sonata form with double exposition. ” This form is common in concerti and one feature of this form is that the first exposition does not end with a double bar and repeat sign indicating a literal repeat of the exposition.
Instead the first exposition is for the orchestra without the soloist, and does not modulate to and conclude in the dominant, but stays in the tonic key throughout. When the soloist enters a second exposition begins which does modulate to the dominant key (or relative major if the work is in a minor key), and the second exposition does indeed cadence in the dominant. The only other variance from a standard (non-concerto) sonata form is the traditional cadenza, which occurs near the end of the recapitulation of the movement. The second theme is presented following a transitional section.
In the first exposition it is in the key of A, but in the second exposition it is heard in the dominant key of E Major. This phrase ends with a half cadence, and the following phrase ends with a PAC, creating a double parallel period. The closing theme is more intense in character and features interplay between the winds and strings as well as frequent use of the borrowed subdominant chord. It includes a number of different melodic ideas and concludes with a strong beat PAC in A Major in measure 62. The second exposition begins in measure 67 with the first theme stated by the solo pianist.
The major difference in this exposition is the modulation to the dominant key of E Major, which takes place in the Transition section in measures 82-98. This second exposition ends in a surprising way in measure 142 with the half cadence falling on the fourth beat of the measure and the music abruptly ceasing, creating a dramatic pause that is followed by an entirely new theme, which begins the development section. This new theme is in E Major and provides virtually all of the melodic harmony heard throughout the development section.
Following this embellished theme in E Major, the music begins to fragment this new theme and moves into key areas associated with the key of A minor as opposed to A Major. The keys touched on include E minor, C Major, F Major, and D minor. An especially nice passage is found in mm. 170-178. It features the clarinet and flute in a canon based on the ‘new’ theme, while the soloist maintains a running sixteenth note figure. Harmonically it begins in the key of D minor and traces the circle of fifths to a cadence on an E major chord in measure 178.
Since E Major is the dominant chord of A Major this initiates a prolongation of the dominant of A Major in measures 178-189. A sort of “mini-cadenza” occurred in 189-198, which leads to the Recapitulation beginning in measure 198. The Recapitulation restates all of the themes heard in the exposition, now all in the key of A Major, with the soloist and orchestra interacting, unlike the first exposition. A particularly long Coda section begins in measure 261 with the reintroduction of the development section’s ‘New’ theme, presented now by the soloist alone, and in the key of A Major for the first time.
Like the beginning of the development section, including the dramatic pause, it is followed by the placid restatement of the ‘New’ theme by the orchestra (290). This breaks off though and leads through a series of forte chords to the traditional tonic 6/4 chord paving the way for the cadenza. The cadenza is fundamentally a greatly expanded prolongation of the V chord. Following the cadenza the orchestra enters in a forte tutti statement with material drawn from the closing theme first presented in measure 49. A decisive PAC in A Major occurs in m. 309 followed by a prolongation of the tonic chord to the movement’s end.