A brief outline of the first movement of one of his concertos will illustrate the manner in which the triplex form was used in all of them, and in which, with few modifications, it has continued to be used by most composers. Let us take the wonderfully delightful concerto in A major (K. 488). The movement opens with a long section for the orchestra. The first theme is announced at once. Later comes the lovely second theme, in the tonic key, be it noted. There is then a short coda, and the orchestra comes to a full tonic cadence and allows the piano to take up the music. The function of this orchestral introduction is to introduce the two themes out of which the movement now proceeds to build itself, conforming pretty closely to the triplex model.
The piano has the first theme practically alone, the orchestra merely suggesting an inner voice in the harmony from time to time. In the transitional passage to the dominant key which follows, the piano serves chiefly to spin a few figures over the chords carried by the orchestra. Then the piano has the second theme, now in the dominant, alone; after which it is repeated by the orchestra, the piano adding a touch of ornamental color here and there. Pianoforte and orchestra now play together, the piano taking the rôle of soloist in a series of scales and figures. A full cadence in E major ends the first section.
The development section is not long. It will be noticed that the pianist is really soloist through it all, the delicate figure work which he has to perform being always evident above the harmonies or themes of the orchestra.
The long opening section for orchestra at the beginning of the concerto is cut down to a few measures in the restatement. The transitional passage between first and second themes is very much shortened likewise. Finally, after the music has progressed duly according to the conventions governing the restatement section in the triplex form, the orchestra makes a pause. Here the pianist is supposed to play what is known as a cadenza—a long passage usually testing both him and his instrument to the limit of their abilities. These cadenzas were commonly improvised, and in them Mozart must have displayed the greatness of his power both as a musician and as a player. The cadenza came to an end with a long trill, after which the orchestra, usually without the piano, added the completing coda.
The second and third movements were usually in some simpler form. The second was most frequently an aria, the third a rondo. The whole was primarily a piece for the virtuoso, while the orchestra, save when announcing themes or playing ritornelles, served mainly as an accompaniment to the brilliant soloist. It might well, be it understood, carry on the thematic development of the music, thus leaving the pianist free to weave every sort of arabesque; but from now on the concerto was a form of music which was deliberately planned to show off the special qualities of a solo instrument.
It was almost inevitable that in most concertos the genuinely musical element should be regarded as of less and less importance. The public expected, and indeed still expects, to hear or even to see a virtuoso display the uttermost limits of his skill in such pieces. The improvised cadenzas were in the hands of most players a nuisance which marred the work as a whole beyond repair. But the Mozart concertos, written as they were for occasions of his public appearance, have a true musical value. We know enough of his improvising to be sure that his cadenzas added and did not subtract from this.
Their chief beauty is here, as in his other music, the melodious freshness of his themes, the delightful subtlety of his harmony. The constant stream of arabesque which the piano adds to this intrinsically beautiful foundation is in the main simple. It is surprising how little Mozart added to the virtuoso style of pianoforte literature, even how little he made use of what, through Clementi and Dussek, was already common property. There are practically no octave passages, and no passages in double notes. He uses only scales, arpeggios and trills.
But his art of combining these with the orchestra has never been excelled. In this regard his concertos stand far above those of the virtuosi like Hummel, Dussek, and John Field. Their tone-color is not only that which the essentially colorless pianoforte can afford; it is a beautiful interweaving of many colors. His treatment of the orchestra is always distinguished, never haphazard or indifferent. Delicate as the coloring may be to ears now accustomed to heavier and more sensuous blendings, it is not watery and faded. It is still exquisitely clear and suggestive. As the first of composers to make such effective use of the cold yet brilliant tone of the pianoforte in combination with the various warmer tones of the orchestra, he may be said to have set a standard of excellence which subsequent concertos have oftener fallen short of than attained. Hundreds have been written. The fingers of one hand might perhaps count the number of those which as works of art are comparable to Mozart’s.
It must be admitted that Mozart was not equally inspired in all his concertos. That in D major (K. 537), composed in 1788 and known as the ‘Coronation Concerto,’ savors unpleasantly of the pièce d’occasion. The themes of the first movement are almost ludicrously commonplace. Those of the Larghetto are hardly more distinguished, and the last movement can be recommended for little more than brilliance. The concertos in D minor (K. 466) and in C minor (K. 491) are, on the contrary, inspired throughout. That in A major (K. 488) one might well be tempted to call the most charming of Mozart’s pianoforte compositions, but that such distinctions are gratuitous and unpleasant. The second theme of the first movement is surely one of the loveliest in all music. The last movement is irresistibly charming, with the sparkle of sunshine on laughing water. The andante between the first and last is of that sort of music which words cannot describe. Indeed there is in all of Mozart’s music, as we have said, a self-sufficient vitality which makes it a perfect satisfaction for the ear. One does not feel stirred to seek a meaning beneath it. It is almost natural music. There is nothing labored, nothing symbolic; and it is almost uniquely beautiful. Surely, as far as pianoforte music is concerned we shall wait nearly half a century before that abstract grace again appears, this time in the works of Frédéric Chopin.