The Sonata for Two Pianos and Percussion is a musical composition by Hungarian pianist and ethnomusicologist Béla Bartók in which the composer combined the folk rhythms of Hungary and his mastery of classical structures with an unusual scoring for two pianos and percussion. This sonata, one of many by Bartók, was written in 1937 and later was arranged for orchestra in addition to the original instruments.
 
Bartók composed the piece for the International Society for Contemporary Music to commemorate the tenth anniversary of its chapter in Basel, Switzerland. The society’s audience was already sympathetic to new music. Still, Bartók’s modern offering — despite its unexpected selection of instruments — was built upon a solid foundation of classical structures that were known to Mozart and Beethoven.
 
The first movement of Bartók’s sonata offers a sonata form, in which two main melodic (or here rhythmic) ideas are stated, varied, and then restated. For the second movement, Bartók used a simpler ternary pattern, in which an initial melody is followed by a second before the first returns almost unchanged. (A Classical era minuet-and-trio movement is quite similar in expression.) The third and final movement draws on elements of the sonata-form idea with the addition of other melodies for even greater variety. It is in this last movement that Bartók’s beloved folk rhythms are most prominent.
 
– Betsy Schwarm, Britannica, 2013