Closely allied with the suite, indeed an offshoot from it, is the sonata, originally any piece for instruments (from _sonare_, to sound or play) as distinguished from a cantata for voices (from _cantare_, to sing). The old sonatas are essentially suites. But the generation after Bach’s, of which one of his own sons, Carl Philipp Emanuel Bach, was a guiding spirit, hit upon one of those apparently simple but immensely fruitful ideas out of which whole schools are made. It was this: Instead of coming to a stop as soon as you have outlined a single musical idea or 'theme,’ and then merely repeating or slightly elaborating it, as was done in all the movements of the typical suite, why not embrace in the span of your thought _two contrasting ideas_,[1] so characterized and arranged that each should serve as the effective foil of the other? Once this notion of making a piece of music out of two contrasting themes was tried out in practice it proved to have endless potentialities. In the two hundred years that have elapsed since C. P. E. Bach’s birth in 1714 its possibilities have not been exhausted; it has shown an elasticity which has enabled it to serve equally for the embodiment of such different ideas as those of Mozart, Beethoven, Schubert, Schumann, Tschaikowsky, Brahms; it has been applied to all branches of instrumental music, extending its sway quickly from the 'sonata,’ specifically so called, for one, two or three instruments, to the quartet, quintet, etc., for a group, to the concerto for a soloist with orchestral accompaniment, and to the overture and the symphony for full orchestra.