Concerto (from the latin concertus, from certare, to strive, also confused with concentus), in its most general sense, is a name for a piece of classical music in which there are two distinct groups of instruments, one larger than the other. The most usual kind of concerto is one that pits a solo instrument against a full orchestra in three movements.
The term appears in the beginning of the 17th century, at first as a title of no very definite meaning, but which early acquired a sense justified by its etymology and became applied chiefly to compositions in which unequal instrumental or vocal forces are brought into opposition.
Although by Johann Sebastian Bach's time the concerto as a polyphonic instrumental form was thoroughly established, the term frequently appears in the autograph title-pages of his church cantatas, even when the cantata contains no instrumental prelude. Indeed, so entirely does the actual concerto form, as Bach understands it, depend upon the opposition of masses of tone unequal in volume with a compensating inequality in power of commanding attention, that Bach is able to rewrite an instrumental movement as a chorus without the least incongruity of style.
A splendid example of this is the first chorus of a university festival cantata, "Vereinigte Zwietracht der weckseinden Saiten," the very title of which ("united contest of turn-about strings") is a perfect definition of the earlier form of concerto grosso, in which the chief mass of the orchestra was opposed, not to a mere solo instrument, but to a small group called the concertino or else the whole work was for a large orchestral mass in which tutti passages alternate with passages in which the whole orchestra is dispersed in every possible kind of grouping.
But the special significance of this particular chorus is that it is arranged from the second movement of the first Brandenburg concerto and that while the orchestral material is unaltered except for transposition of key, enlargement of force and substitution of trumpets and drums for the original horns, the whole chorus part has been evolved from the solo part for a kit violin (violino piccolo).
This admirably illustrates Bach's grasp of the true idea of a concerto, namely, that whatever the relations may be between the forces in respect of volume or sound, the whole treatment of the form must depend upon the healthy relation of function between that force which commands more and that which commands less attention. Ceteris paribus the individual, suitably placed, will command more attention than the crowd, whether in real life, drama or instrumental music. And in music the human voice, with human words, will thrust any orchestral force into I the background, the moment it can make itself heard at all.
Hence it is not surprising that the earlier concerto forms should show the closest affinity (not only in general aesthetic principle, but in many technical details) with the form of the vocal aria, as matured by Alessandro Scarlatti. And the treatment of the orchestra is, multatis mutandis, exactly the same in both.
The orchestra is entrusted with a highly pregnant and short summary of the main contents of the movement, and the solo, or the groups corresponding thereto, will either take up this material or first introduce new themes to be combined with it, and, in short, enter into relations with the orchestra very like those between the actors and the chorus in Greek drama.
If the aria before Mozart may be regarded as a single large melody expanded by the device of the ritornello so as to give full expression to the power of a singer against an instrumental accompaniment, so the polyphonic concerto form may be regarded as an expansion of the aria form to a scale worthy of the larger and purely instrumental forces employed, and so rendered capable of absorbing large polyphonic and other types of structure incompatible with the lyric idea of the aria.
The da capo form, by which the aria had attained its full dimensions through the addition of a second strain in foreign keys followed by the original strain da capo, was absorbed by the polyphonic concerto on an enormous scale, both in first movements and finales (see Bach's Klavier concerto in E, Violin concerto in E, first movement), while for slow movements the ground bass diversified by changes of key (Klavier concerto in D minor), the more melodic types of binary form, sometimes with the repeats ornamentally varied or inverted (Concerto for 3 klaviers in D minor, Concerto for klavier, flute and violin in A minor), and in finales the rondo form (Violin concerto in E major, Klavier concerto in F minor) and the binary form (3rd Brandenburg concerto) may be found.
When conceptions of musical form changed and the modern sonata style arose, the peculiar conditions of the concerto gave rise to problems the difficulty of which only the highest classical intellects could appreciate or solve. The number and contrast of the themes necessary to work out a first movement of a sonata are far too great to be contained within the single musical sentence of Bach's and George Friderich Handel's ritornello, even when it is as long as the thirty bars of Bach's Italian concerto (a work in which every essential of the polyphonic concerto is reproduced on the harpsichord by means of the contrasts between its full register on the lower of its two keyboards and its solo stops on both).
Bach's sons had taken shrewd steps in forming the new style; and Mozart, as a boy, modelled himself closely on Johann Christian Bach, and by the time he was twenty was able to write concerto ritornellos that gave the orchestra admirable opportunity for asserting its character and resource in the statement in charmingly epigrammatic style of some five or six sharply contrasted themes, afterwards to be worked out with additions by the solo with the orchestra's co-operation and intervention.
As the scale of the works increases the problem becomes very difficult, because the alternation between solo and tutti easily produces a sectional type of structure incompatible with the high degree of organization required in first movements; yet frequent alternation is evidently necessary, as the orchestral solo is audible only above a very subdued orchestral accompaniment, and it would be highly inartistic to use the orchestra for no other purpose. Hence in the classical concerto the ritornello is never abandoned, in spite of the enormous dimensions to which the sonata style expanded it.
And though from the time of Mendelssohn onwards most composers have seemed to regard it as a conventional impediment easily abandoned, it may be doubted whether any modern concerto, except the four magnificent examples of Johannes Brahms, and Dr Joachim's Hungarian concerto, possesses first movements in which the orchestra seems to enjoy breathing space. And certainly in the classical concerto the entry of the solo instrument, after the long opening tutti, is always dramatic in direct proportion to its delay.
The great danger in handling so long an orchestral prelude is that the work may for some minutes be indistinguishable from a symphony and thus the entry of the solo may be unexpected without being inevitable. This is especially the case if the composer has treated his opening tutti like the exposition of a sonata movement, and made a deliberate transition from his first group of themes to a second group in a complementary key, even if the transition is only temporary, as in Ludwig van Beethoven's C minor concerto.
Mozart keeps his whole tutti in the tonic, relieved only by his mastery of sudden subsidiary modulation; and so perfect is his marshalling of his resources that in his hands a tutti a hundred bars long passes by with the effect of a splendid pageant, of which the meaning is evidently about to be revealed by the solo. After the C minor concerto, Beethoven grasped the true function of the opening tutti and enlarged it to his new purposes. With an interesting experiment of Mozart's before him, he, in his G major concerto, Op. 53, allowed the solo player to state the opening theme, making the orchestra enter pianissimo in a foreign key, a wonderful incident which has led to the absurd statement that he abolished the opening tutti, and that Mendelssohn in so doing has followed his example.
In this concerto he also gave considerable variety of key to the opening tutti by the use of an important theme which executes a considerable series of modulations, an entirely different thing from a deliberate modulation from material in one key to material in another. His fifth and last piano concerto, in E flat, commonly called the Emperor, begins with a rhapsodical introduction of extreme brilliance for the solo player, followed by a tutti of unusual length which is confined to the tonic major and minor with a strictness explained by the gorgeous modulations with which the solo subsequently treats the second subject.
In this concerto, Beethoven also dispenses with the only really conventional feature of the form, namely, the cadenza, a custom elaborated from the operatic aria, in which the singer was allowed to extemporize a flourish on a pause near the end. A similar pause was made in the final ritornello of a concerto, and the soloist was supposed to extemporize what should be equivalent to a symphonic coda, with results which could not but be deplorable unless the player (or cadenza writer) were either the composer himself, or capable of entering into his intentions, like Joachim, who has written the finest extant cadenza of classical violin concertos.
Brahms's first concerto in D minor, Op. 15, was the result of an immense amount of work, and, though on a mass of material originally intended for a symphony, was nevertheless so perfectly assimilated into the true concerto form that in his next essay, the violin concerto, Op. 77, he had no more to learn, and was free to make true innovations. He succeeds in presenting the contrasts even of remote keys so immediately that they are serviceable in the opening tutti and give the form a wider range in definitely functional key than any other instrumental music. Thus in the opening tutti of the D minor concerto the second subject is announced in B flat minor.
In the B flat piano concerto, Op. 83, it appears in D minor, and in the double concerto, Op. 102, for violin and violoncello in A minor it appears in F major. In none of these cases is it in the key in which the solo develops it, and it is reached with a directness sharply contrasted with the symphonic deliberation with which it is approached in the solo. In the violin concerto, Op. 77, Brahms develops a counterplot in the opposition between solo and orchestra, inasmuch as after the solo has worked out its second subject the orchestra bursts in, not with the opening ritornello, but with its own version of the material with which the solo originally entered.
In other words we have now not only the development by the solo of material stated by the orchestra but also a counter-development by the orchestra of material stated by the solo. This concerto is, on the other hand, remarkable as being the last in which a blank space is left for a cadenza, Brahms having in his friend Joachim a kindred spirit worthy of such trust. In the piano concerto in B flat, and in the double concerto, Op. 102, the idea of an introductory statement in which the solo takes part before the opening tutti is carried out on a large scale, and in the double concerto both first and second subjects are thus suggested.
It is unnecessary to speak of the other movements of concerto form, as the sectional structure that so easily results from the opposition between solo and orchestra is not of great disadvantage to slow movements and finales, which accordingly do not show important differences from the ordinary types of symphonic and chamber music. The scherzo, on the other hand, is normally of too small a range of contrast for successful adaptation to concerto form, and the solitary great example of its use is the second movement of Brahms's B flat piano concerto.
Nothing is more easy to handle with inartistic or pseudoclassic effectiveness than the opposition between a brilliant solo player and an orchestra; and, as the inevitable tendency of even the most artistic concerto has been to exhaust the resources of the solo instrument in the increased difficulty of making a proper contrast between solo and orchestra, so the technical difficulty of concertos has steadily increased until even in classical times it was so great that the orthodox definition of a concerto is that it is an instrumental composition designed to show the skill of an executant, and one which is almost invariably accompanied by orchestra.
This idea is in flat violation of the whole history and aesthetics of the form, which can never be understood by means of a study of averages. In art the average is always false, and the individual organization of the greatest classical works is the only sound basis for generalizations, historic or aesthetic.