The development of the Viennese Classical style can almost be traced back in the violin and keyboard works of Mozart himself, since he wrote examples of the form throughout his creative life, and they provide a telling and comprehensive survey of his development in one particular field. His first four sonatas, K. 6-9, were published in Paris in 1764 as opp. 1 and 2. Leopold Mozart wrote enthusiastically of ‘the furore they will make in the world when people read on the title-page that they have been composed by a seven-year-old’, but it seems likely that Leopold himself contributed to their composition. With their cheerful Alberti basses in the piano and modest contributions from the violin, these sonatas are not really remarkable, yet it is notable how, even so early, Mozart makes the violin at least contribute something to the texture: a little echo in K.6, imitative textures in K.8. The chiming sixths have been anticipated in J.C. Bach’s accompanied sonatas, but the sturdiness of K.7’s first movement and its perky little second minuet surely have Mozart’s own imprint. It is most unusual to find the second minuet of K.8 in the key of B flat minor; all these sonatas, including the last G major K.9 (which is the least inventive), end with a pair of minuets.

THe sonatas K.10-15, which also include ad libitum cello parts, should perhaps be mentioned here; they appeared in London in 1765. But the next set of violin sonatas proper is K.26-31, published in the Hague a year later as Mozart’s op. 4. Already in K.26 in E flat, the violin imitates the keyboard entry, though it then confines itself to brittle repeated notes–which may help to explain why composers often asked that in such accompanied sonatas the violin should use a mute. The final movement of this sonata is a witty Rondeau in which the violin acts as it were a tutti section. A more interesting sharing of material occurs in the first movement of K.28 in C, where shooting scales asnwer each other in keyboard and violin; in the second movement, an allegro grazioso, the violin is given an equal share in the thematic material. There is a litle more imitative work in the D major sonata K.29, though in K.30 in F major most of the attentio n is on the keyboard player’s elegant cross-hand writing. Typically Mozartian is the energy and essentially simple harmoic framework ok K.31 in B flat; this sonata is concluded by a movement in a form which will become familiar, the theme and variations, though the violin is allowed little in the way of an independent contribution.

The sonatas K.55-60 are now believed to be spurious: Alfred Einstein for a while thought they might be by Joseph Schuster, whose violin sonatas praised in a letter home (‘They are not bad. If I stay on I shall write six myself in the same style, as they are very popular here’). But that has now been disproven, and the works remain anonymous. For the next authenticated set of sonatas we must move on more than a decade to those published in paris in 1778, again as op.1. The first three were probably written in Mannheim in early 1778, and the remaining three added in Paris in the summer. At once here we can observe the emancipation of the violin from its accompanying role. It announces the open, singing melody of the sonata K.301 in G, and though it frequently joins in the accompaniment during the sonata, it has a tune of its own in the middle section of the triple-time Allegro. The first movement of this sonata shows a form closer to ritornello structure of the concerto than to sonata form.

The opening of the E flat sonata K.302 is familiar from Mozart’s symphonic style at this time: an elaborated, vigorous descending arperggio. Here the violin has horn calls and energetic triplets, and there is a most marvellous transition back to the second subject in the recapitulation. Although absolutely no violinistic tricks were needed (which would put the music out of the reach of the amateur), Mozart is already exploiting the nistrument’s special possibilities. In the finale it doubles the keyboard an octave below. The third of this set, K.303 in C, unusually has a slow introduction which most ingeniously first stabilizes the key of C, then leads away from it to a cadence towards G, and introduces the Allegro with maximum instability by taking the G, sharpening it, and leading from E minor into A minor. The Adagio recurs in mid-sonata (like that in Haydn’s ‘Drumroll’ symphony and one of the pieces from Scuster’s set) and this time leads to a C to C sharp and then D minor. A confident C major is nevertheless restored before the close, and the final Minuet is tonally unremarkable.
Though these sonatas have their impressive moments, nothing in them prepares us for the shock of the E minor sonata K. 304,which is among Mozart’s most impressive creations in any form. It may be unwise to link it directly with the period following the death of his mother in Paris in July 1778; it can be dated, however, to within a month both of his bereavement and of that other outburst in the minor mode, the A minor piano sonata K. 310. E minor is a most unusual key for Mozart; indeed the only parallel for the key and expressive content of this remarkable sonata is Haydn’s Trauer symphony no. 44 of around 1772: could Mozart have known it? Like the finale of that symphony, this sonata’sfirst movement opens with a suppressed, tortured unison, and then bursts out forte. Mozart’s resourcefulness (and also his avoidance of predictable sonata contrasts) is exemplified by his wonderfully varied treatment of this opening unison theme. After the initial outburst, the violin takes it up over a smooth keyboard accompaniment; it returns in canon, in G major, modulating to B, to cadence the first half. The piano opens the development alone with the theme, where it forms the basis of a short but highly expressive imitative section with strong dissonances. The master-stroke comes at the moment of recapitulation, however: Mozart gives the phrase to the violin alone; but as it reaches the highest note, he sends the piano crashing in with an extraordinary chord (which can only be described as an altered 6/5), in a rhythmic figure which is repeated three times to harmonize the rest of the theme. Even then Mozart has not quite finished with his surprises: as a coda, the theme enters again, quietly in the violin, over another fluctuating accompaniment of infinite peace.
The minuet which ends this strange sonata is scarcely less remarkable. Its spirit is almost Baroque, and its material uses the Baroque descending tetrachord to underline its harmonies.