154. A trio is a sonata for three instruments (such as piano, violin, and cello), while a quartet is a sonata for four instruments, the most common quartet combination being as follows: First and second violins, viola, and violoncello.
The term chamber music is often applied to instrumental music for trio, quartet, quintet, and other similar combinations which are suitable for a small room rather than for a large concert hall.
The words trio and quartet are also applied to vocal works for three and four voices respectively, these having no relation whatsoever to the sonata as described above. The word trio is also applied to the middle section of minuets, scherzas, marches, etc., the term originating in the old usage of writing this part for three instruments only.
155. A concerto is a sonata for a solo instrument with orchestral accompaniment, the form being usually somewhat modified so as to adapt it to a composition in which there must necessarily be opportunity for a good deal of technical display. There are usually but three movements in the concerto.
The great majority of concertos are for piano and orchestra, but examples of concertos for violin, cello, flute, oboe, and other solo instruments (all with orchestral accompaniment) have also been written. A few modern composers have applied the term concerto to certain large organ works (with no orchestral accompaniment, the composition being written for just the one instrument), but this use of the word is so contrary to the accepted definition that it is hardly justifiable.
When a concerto is played on two pianos (without orchestra), this does not mean that there is no orchestral part, but that there is no orchestra to play it, and so the parts that should be played by the orchestral instruments have simply been arranged for a second piano (sometimes organ).
156. A symphony is a sonata for full orchestra. In general its construction is the same as that of the sonata, but it is usually of much larger proportions and has in it much greater variety of both tonal and rhythmic material. The symphony is generally conceded to be the highest type of instrumental music ever evolved.
The symphony was accepted as a standard form in the time of Haydn (1732-1809) and was developed enormously by Haydn himself, Mozart (1756-1791), and Beethoven (1770-1827), reaching perhaps its highest point in the famous "Nine Symphonies" of the last-named composer. Later symphony writers whose works are at present being performed include Schumann, Tschaikowsky, and Dvořák.
The word symphony was formerly used synonymously with ritornelle, both words being applied to instrumental interludes between parts of vocal works, but this usage has now entirely disappeared.
[157.] Sonata-form (sometimes called sonata-allegro) is a plan for the construction of instrumental music (sonatas, quartets, symphonies, etc.), in which three rather definite divisions always occur, the third division being a more or less literal repetition of the first.