It was once thought that all six of J.S. Bach's trio sonatas for organ (BWV 525-530) were composed in or about 1727; now, however, the period during which he is believed to have worked on these fascinating pieces has been expanded, and a composition date as late as 1731 has been assigned to the Trio Sonata for organ No. 5 in C major, BWV 529. It is, like the others of the set, a work in three movements in which the traditional three voices of the Baroque trio sonata are all assigned to a single keyboard player -- one upper instrument voice for each hand and the basso continuo to the feet (pedals). And so, in typical Johann Sebastian fashion, something very new is created from something very old -- and this process represents an important, if not widely known, step in the evolution of the sonata as it is now generally understood.
Freshness of instrumentation and layout aside, the music of BWV 529 is representative of the Baroque chamber sonata tradition. The normal sonata-style imitative gesture is made to open the Allegro first movement; here a bit of invertible counterpoint is used, the second voice entering before it properly "should," to add a little interest to the standard technique. The main subject of the movement has two distinct elements to it: sixteenth notes that oscillate around a fixed internal pedal point and a follow-up idea in bouncy eighth notes. Precious little material is added as the movement moves forward -- what we have is essentially an ingenious 155-bar working-out of just two contrasting thoughts.
The following Largo is as florid a movement as is to be found in the organ sonatas; the two highly ornamented upper voices weave in and around one another atop a steady bass line. The Allegro finale is the most typical trio-sonata movement in BWV 529; one can indeed imagine the opening bars having been penned by Arcangelo Corelli, though the following compact and elaborate working-out of this basic contrapuntal cell would have been entirely beyond the scope of the Roman master.