The period which this and the following chapters attempt to describe is dominated by the sonata form. Not a composer of instrumental music--and it was essentially the age of instrumental music--but essayed that form in various guises. Even the writers of opera did not fail to adopt it in their instrumental sections, and even in their arias. But the decades which are our immediate concern represent a formative stage, because there is much variety, much uncertainty, both in nomenclature and in the matter itself. Nomenclature is never highly specialized at first. A name primarily denotes a variety of things which have perhaps only slight marks of resemblance. Thus we have seen how _sonata_, derived from the verb _suonare_, to sound, is at first a name for any instrumental piece, in distinction to _cantata_, a vocal piece. The _canzona da sonar_ (or _canzon sonata_) symbolized the application of the vocal style to instruments, and the abbreviation ‘sonata’ was for a time almost synonymous with _sinfonia_, as in the first solo sonatas (for violin) of Bagio Marini about 1617. The sonata in its modern sense is essentially a solo form; but, during a century or more of its evolution, the most familiar guise under which it appeared was the ‘trio-sonata.’ That, as we have seen, broadened out to symphonic proportions (while adapting some of the features of the orchestral suite) and the sonata became more specifically a solo piece, or, better, a group of pieces, for the sonata of our day is a ‘cyclical’ piece. But through all its outward manifestations, and irrespective of them, it underwent a definite and continuous metamorphosis, by which it assumed a more and more definite pattern, or patterns, which eventually fused into one.