The Sonata in C major for piano four-hands, D 812 (Op. posth. 140) by Franz Schubert, also known as Grand Duo, is one of Schubert's most important works for two pianists. It was the successor to the composer's 1818 sonata for piano four-hands in B-flat major.
At the time this work was written Schubert was too ill to play piano. He complained of pain in his bones and his left arm, headaches, and lesions in his mouth and throat. In a letter to his brother Ferdinand he described his illness as "a period of fateful recognition of a miserable reality, which I endeavour to beautify as far as possible by my imagination."
The sonata was published after Schubert's death, in 1837, when it was printed with the title 'Grand Duo' - by which it is still popularly known, though there is no evidence that this was Schubert's title.
There are four movements:
This is a mature and characteristic work by Schubert on the largest scale. The structures of the movements closely resemble those of a symphony and some passages appear to reproduce orchestral effects (though both these observations might apply to some of Schubert's solo piano sonatas). Thus in addition to its intrinsic qualities and interest the Grand Duo was soon believed by some authorities, including Robert Schumann, to be a transcription or draft of the missing so-called Gastein Symphony that Schubert was thought to have written in 1824. (It is only since the 1970s that it has been proved conclusively that there was no such work.) As a result, there have been a number of orchestral realizations of the Sonata as a symphony. The best known is by Joseph Joachim (1855), which was conducted by Brahms several times in the 1870s and later recorded by Arturo Toscanini. Other completions are by Anthony Collins (1939),Marius Flothuis (1940-42),Karl Salomon (1946),Fritz Oeser (1948),René Leibowitz (c.1965),Felix Weingartner, and most recently Raymond Leppard. Joachim altered the tempo of the finale to Allegro moderato.
The finale, like that of the B-flat sonata for solo piano (D. 960) from the composer's last year, opens deceptively in the wrong key, in this case, the relative minor, A minor (in the later solo sonata, after a unison G, the melody opens in the supertonic, C minor). In both cases, however, the harmonic deception is almost immediately 'corrected' by shifting to the main key.
A typical performance takes about 40 minutes.