These writers of violin sonatas were just touching on the clear realisation of harmonic form as accepted in modern times, and they sometimes adopted the later type, though rarely, and that obscurely; they mastered the earlier type, and used it freely; and they also used the intermediate type which combines the two, in which the principal or first subject makes its appearance both at the beginning of the first half and near the end, where a modern would expect it. As a sort of embryonic suggestion of this, the Tempo di Gavotta, in the eighth Sonata of Corelli's Opera Seconda, is significant. Complete examples are—the last movement of Tartini's fourth Sonata of Opus 1, and the last movement of that in D minor above referred to; the last movement of Geminiani's Sonata in C minor; the main portion, excluding the Coda, of the Corrente in Vivaldi's Sonata in A major; the last movement of a Sonata of Nardini's, in D major; and two Capriccios in B♭ and C, by Franz Benda, quoted in F. David's 'Hohe Schule,' etc.
The four-movement type of violin sonata was not invariably adopted, though it preponderates so conspicuously. There is a set of twelve sonatas by Locatelli, for instance, not so fine as that in F. David's collection, which are nearly all on an original three-movement plan, concluding with an 'Aria' and variations on a ground-bass. Some of Tartini's are also in three movements, and a set of six by Nardini are also in three, but always beginning with a slow movement, and therefore, though almost of the same date, not really approaching the distribution commonly adopted by Haydn for Clavier Sonatas. In fact the old Violin Sonata is in many respects a distinct genus, which maintained its individuality alongside the gradually stereotyped Clavier Sonata, and only ceased when that type obtained possession of the field, and the violin was reintroduced, at first as it were furtively, as an accompaniment to the pianoforte. The general characteristics of this school of writers for the violin, were nobility of style and richness of feeling, an astonishing mastery of the instrument, and a rapidly-growing facility in dealing with structure in respect of subject, key, modulation and development; and what is most vital, though less obvious, a perceptible growth in the art of expression and a progress towards the definition of ideas. As a set-off there are occasional traces of pedantic manners, and occasional crudities both of structure and expression, derived probably from the associations of the old music which they had so lately left behind them. At the crown of the edifice are the Sonatas of J. S. Bach. Of sonatas in general he appears not to have held to any decisive opinion. He wrote many for various instruments, and for various combinations of instruments. For clavier, for violin alone, for flute, violin, and clavier, for viol da gamba and clavier, and so on; but in most of these the outlines are not decisively distinct from Suites. In some cases the works are described as 'Sonatas or Suites,' and in at least one case the introduction to a church cantata is called a Sonata. Some instrumental works which are called Sonatas only, might quite as well be called Suites, as they consist of a prelude and a set of dance-tunes. Others are heterogeneous. From this it appears that he had not satisfied himself on what lines to attack the Sonata in any sense approaching the modern idea. With the Violin Sonatas it was otherwise; and in the group of six for violin and clavier he follows almost invariably the main outlines which are characteristic of the Italian school descended from Corelli, and all but one are on the four-movement plan, having slow movements first and third, and quick movements second and fourth. The sixth Sonata only differs from the rest by having an additional quick movement at the beginning. Not only this but the second movements keep decisively the formal lineaments of the ancient type of free fugue, illustrated with more strictness of manner by the Canzonas. Only in calibre and quality of ideas, and in some peculiar idiosyncrasies of structure do they differ materially from the works of the Italian masters. Even the first, third, and fifth Sonatas in the other set of six, for violin alone, conform accurately to the old four-movement plan, including the fugue in the second place; the remaining three being on the general lines of the Suite. In most of the Sonatas for violin and clavier, the slow movement is a tower of strength, and strikes a point of rich and complex emotional expression which music reached for the first time in Bach's imagination. His favourite way of formulating a movement of this sort, was to develop the whole accompaniment consistently on a concise and strongly-marked figure, which by repetition in different conditions formed a bond of connection throughout the whole; and on this he built a passionate kind of recitative, a free and unconstrained outpouring of the deepest and noblest instrumental song. This was a sort of apotheosis of that form of rhapsody, which has been noticed in the early Sonatas, such as Biber's and Kuhnau's, and was occasionally attempted by the Italians. The six Sonatas present diversities of types, all of the loftiest order; some of them combining together with unfailing expressiveness perfect specimens of old forms of contrapuntal ingenuity. Of this, the second movement of the second Sonata is a perfect example. It appears to be a pathetic colloquy between the violin and the treble of the clavier part, to which the bass keeps up the slow constant motion of staccato semiquavers: the colloquy at the same time is in strict canon throughout, and, as a specimen of expressive treatment of that time-honoured form, is almost unrivalled.
In all these movements the kinship is rather with the contrapuntal writers of the past, than with the types of Beethoven's adoption. Even Bach, immense as his genius and power of divination was, could not leap over that period of formation which it seems to have been indispensable for mankind to pass through, before equally
