The Trio Sonata in the Baroque Period

Trio Sonata is an instrumental piece [consisting] of two, three, or four successive movements of different character, which has one or more melody parts, with only one player to a part [i.e., "einfach" as against Mattheson’s "stark," for multiple performance of the parts. Cf. SBE 25]. Depending on the number of concertante, melody parts that it has, a sonata is described as [being] à solo, à due, à tré, etc. Clearly, in no form of instrumental music is there a better opportunity than in the sonata to depict feelings without [the aid of] words. The symphony [and] the overture has a more fixed character. The form of a concerto seems designed more to give a skilled player a chance to be heard against the background of many instruments than to implement the depiction of violent emotions. Aside from these [forms] and the dances, which also have their special characters, there remains only the form of the sonata, which assumes [any or] all characters and every [kind of] expression. By [means of] the sonata the composer can hope to produce a monologue through tones of melancholy, grief, sorrow, tenderness, or delight and joy. or maintain a sensitive dialogue solely through impassioned tones of similar or different qualities. or simply depict emotions [that are] violent, impetuous, and [sharply] contrasted, or light, gentle, fluent, and pleasing. To be sure, [even] the weakest composers have such goals in the making of sonatas, among the weakest [being] the Italians and those who imitate them. The sonatas of the present-day Italians are characterized by a bustle of sounds succeeding each other arbitrarily without any other purpose than to gratify the insensitive ear of the layman, [and] by sudden, fantastic transitions from the joyous to the mournful, from the pathetic to the flirtatious, without our getting what the composer wants [to say]. And if the performance of these [sonatas] engages the fancy of a few hotheads, the heart and imagination of every listener of taste or understanding will still remain completely untouched.
A large number of easy and hard keyboard [i.e., clavichord] sonatas by our Hamburg [Emanuel] Bach show how character and expression can be brought to the sonata. The majority of these are so communicative ["sprechend"] that one believes [himself] to perceive not tones but a distinct speech, which sets and keeps in motion our imagination and feelings. Unquestionably, to create such sonatas requires much genius [and] knowledge, and an especially adaptable and alert sensibility. But they also