Eighteen years before Beethoven wrote the first duo sonatas for cello and piano, discussed in the previous chapter, Mozart had composed his first real duos for violin and piano: six sonatas, k301–6, written in 1778, partly in Mannheim and partly in Paris and published the same year. In a letter to his father and sister, dated 6 October 1777, he described ‘six duets for clavicembalo and violin by Schuster, which I have often played here. They are not bad. If I stay on, I shall write six myself, as they are very popular here.’ Mozart, who like Beethoven was both a pianist and a violinist, took his new violin sonatas seriously, composing several more over the next eleven years. Among them are some of his most beautiful chamber works, with independent parts for each instrument – a point noted by a perceptive critic, who described the Mannheim sonatas as ‘the only ones of their kind … the accompaniment of the violin is so artfully combined with the clavier part that both instruments are kept constantly on the alert so that these sonatas require just as skilful a player on the violin as on the clavier.’

Other composers were working along similar lines, among them Beethoven's teacher in Bonn, Christian Gottlob Neefe, who published six violin sonatas in 1776, and the Bonn Kapellmeister, Andrea Lucchesi, who wrote a Sonata facile in the mid-1780s – ‘good evidence’, Sieghard Brandenburg suggests, ‘that dialogue writing for piano and obbligato violin had become generally accepted outside Vienna.’ There is persuasive evidence too that Beethoven knew several of Mozart's violin sonatas. For example, a phrase in the first movement of the Sonata in E flat major, op. 12 no. 3 (ex. 7.1a) almost exactly mirrors part of the first subject in Mozart's Violin Sonata in E minor, k304 (ex. 7.1b).

Moreover, the thoughtful Adagio in the same Beethoven sonata, with its long elegiac melody (ex. 7.2a), is similar in mood and contour to another of Mozart's violin sonatas (ex. 7.2b).