The Grand Duo, which is called well Sonata, is a four-movement piece that Schubert wrote in 1817, after the sonatinas, which he wrote in March and April of 1816. The sonatinas were often called sonatas and since Schubert wanted to make a distinction between the three smaller pieces and this big Sonata he sometimes referred to this piece as the 'Grand Duo'
The first movement starts with the piano playing an accompaniment theme. Which has a typical rhythm that the violin follows after the entrance in the fourth bar. It is a highly communicative piece between both instruments and is characterized by the typical Schubertian lyricism. The characters change often in this movement, something that he did less in his sonatinas.
The second movement is a very fast Scherzo, with a Trio section, that has the tempo indication of Scherzo. It is a happy movement with funny aspects to it. It is a technically demanding piece for the violin. It is interesting that he used the Scherzo as the second movement, which he wrote as third movements in the sonatinas, similar to Beethoven's way of using the Scherzo.
The third movement is the slowest movement of the piece. Schubert marked it as an Andantino in a 3/8 metre. This movement has parts that we could compare metaphorically with waves. It continues always at the same pace. Melodically both instruments respond in a wonderful way with each other making it a very communicative piece.
The fourth movement, which concludes the piece is written in an Allegro Vivace. It reminds us of Beethoven's style. The beginning has elements of the second movement. In some parts, this movement hints towards the minuet form which has the emphasis on the third and first beat.