Mozart’s concertos for the piano and also those for the violin were written primarily for his own use. The best of them date from the period preceding his Paris journey, when he expected to make practical use of them, for he was a virtuoso of no mean powers on both instruments. There are six concertos for either instrument, every one full of pure beauty and a model of form. In them he substituted the classic sonata form for the variable pattern used in the earlier concertos, and hence he may be considered the creator of the classic concerto, his only definite contribution to the history of form. They are not merely brilliant pieces for technical display, but symphonic, both in proportion and import. In them are found some of the finest moments of his inspiration. ‘It is the Mozart of the early concerti to whom we owe the imperishable matter of the Viennese period,’ says Mr. Hadow, ‘and the influences which helped to mold successively the style of Haydn, Beethoven, and Schubert.’
Of Mozart’s symphonies and serenades, terms which in some cases are practically synonymous, there are about eleven that are of lasting value and at least three that are imperishable. With the exception of the Paris symphony, ‘a brilliant and charming pièce d’occasion,’ which was referred to above, all of them were written during the Vienna period, and the three great ones flowed from the composer’s pen within the brief space of six weeks in 1787, the year of Don Giovanni. In the matter of form again Mozart followed in the tracks of the Mannheim school. The usual three movements remain, but, like Haydn, he usually adds the minuet after the slow movement. The ‘developed ternary form’ is applied in the first and more and more frequently also in other movements, especially the last, where it takes the place of the lighter rondo. But the musical material is richer and its handling far more ingenious than that of his predecessors, just as the spiritual import is much deeper. The movements are more closely knit, they have a unity of emotion which clearly points in the direction of Beethoven’s later works. There is, if not an idée fixe, at any rate a sentiment fixe. It is manifested in a multiplicity of ways: more consistent use of the principal thematic material in the ‘working-out,’ reassertion of themes after the ‘transition’ (the section leading from the exposition to the development), introductions which are, as it were, improvisations on the mood of the piece, and codas ‘summing up’ the subjective matter. This same unity exists between the different movements; a note of grief or passion sounded in the first movement is either reiterated in the last or else we feel that the composer has emerged from the struggle in triumph or noble joy. Only the minuet, an almost constant quantity with Mozart, brings a momentary relief or abandon to a lighter vein, if it is not itself, as in the G minor symphony, nobly dignified and touched with sadness.
In the use of orchestral instruments, too, Mozart emulated the practice of the Mannheim composers. Their works were usually scored for eight parts, that is, two oboes or flutes and two horns, besides the usual string body. Clarinets were still rare at that time, and parts provided for them were for that reason arranged for optional use, being interchangeable with the oboe parts. Mozart, although he had heard them as early as 1778 at Mannheim, used them only in his later works,[46] and even then did not often employ that part of their range which reaches below the oboe’s compass (still thinking of them as alternates for that instrument). But in the manner of writing for instruments Mozart’s works show a real novelty. In the Mannheim symphonies the wood wind instruments usually doubled the string parts, but occasionally they were given long, sustained notes and the brass even went beyond mere ‘accent notes’ (di rinforza) to the extent of an occasional sustained note or any individual motive. Haydn and Mozart at first confirmed this practice, but in their later works they introduced a wholly new method, which Dr. Riemann calls ‘filigree work’ and which formed the basis of Beethoven’s orchestral style. ‘The idea to conceive the orchestra as a multiplicity of units, each of which may, upon proper occasion, interpose an essential word, without, however, protruding itself in the manner of a solo and thus disturbing in any way the true character of the symphonic ensemble, was foreign to the older orchestral music.’[47] A mere dialogue between individual instruments or bodies of instruments was, of course, nothing new, but the cutting up of a single melodic thread and having different instruments take it up alternately, as Haydn did, was an innovation, and immediately led to another step, viz., the interweaving of individual melodic sections, dove-tail fashion, thus:
Haydn: Finale, 36th Symphony
and this in turn brought, with Mozart, the coöperation of groups of instruments in such dove-tail formations, and led finally to the more sophisticated disposition of instrumental color, as in the second theme of the great G minor symphony:
This sort of figure has nothing in common with the old polyphony, in which there is always one predominating theme, shifting from one voice to another. The equal and independent participation of several differently colored voices in the polyphonic web is the characteristic feature of modern orchestral polyphony, the style of Beethoven and his successors down to Strauss.