Bach composed his Double Keyboard Concerto circa 1736 in Leipzig. There are surviving copies of the score of the concerto recorded by Bach’s pupil and son-in-law Johann Christoph Altnikol. Following the composer’s death they came into the hands of one of Bach’s youngest sons, the eighteen-year-old Johann Christoph Friedrich who went to work in Bückeburg.
It is believed that the concerto for two keyboards is a reworking of the lost Concerto for Oboe and Violin (or for two violins). That version has been reconstructed and is performed almost as frequently as the keyboard version. But if, at the time, violin and oboe concerti were produced in great volumes, then those for keyboard were a total innovation. The keyboard was not considered a solo instrument and, as a rule, performed the role of the basso continuo. In the Concerto in C Minor Bach dazzlingly gave this role to the two soloists: one of the four hands performs the bass and the three other hands are freely-voiced, depicting a deeply polyphonic structure. In the second movement, against the background of the pizzicato of the bowed instruments, the two keyboards perform a richly ornamented “endless melody”. In the finale, composed using a bourée rhythm, Bach returned to the technique employed in the first movement, as before combining the instruments here and attaining vivid dynamic contrasts.
Mozart’s Double Keyboard Concerto was composed no later than 1779; in 1780 the concerto was published by Johann Anton André in the town of Offenbach. In this concerto the pianist must have absolute mutual understanding and, preferably, also equal abilities. It is as if Mozart was setting an almost immutable law for himself – what appeared in one part had to appear in the other, which makes the musical form measured and almost symmetrically set out.
In the first movement both pianos often seem to be an independent ensemble and appear to forget about the string section and the six wind instruments, performing their “solo for two”. The orchestra makes itself known with the powerful introductory tuttis and with touching high notes from the oboe after which the parity returns.
In Salzburg this concerto could be performed by Mozart and his sister Nannerl. Having only just established himself in Vienna in 1781, Mozart found among his students a new worthy partner. On 23 November he performed the Concerto in E Flat Major with Josepha Barbara von Auernhammer at her home, and on 26 May 1782 they repeated the experience at a concert held in the pavilion in the Augarten Park.