Baroque opera seria, as we have seen (page 137), employs two elements in alternation: recitatives for the dialogue and the action, and numbers that are fully musical — almost always arias — for static meditation and “tableaus” of emotional expression. Classical opera buffa works with the same elements, except that the fully musical numbers include ensembles as well as solo arias.

An ensemble is a number sung by two or more people. And given the Classical composers’ skill in incorporating contrast into their music, they were able to make their ensembles depict the different sentiments of the participating characters simultaneously. This meant that sentiments could be presented much more swiftly and vividly: swiftly, because we don’t have to wait for the characters to sing whole arias to find out what they are feeling, and vividly, because the sentiments stand out in sharp relief one against the other.

The music also depicts these sentiments in flux. For in the course of an ensemble, the action proceeds and the situation changes. And changing sentiments are usually projected by means of new musical sections with different tempos, keys, and themes. A Classical opera ensemble, then, is a sectional number for several characters in which the later sections represent new plot action and the characters’ new reactions to it.

Think back to the da capo aria of Baroque opera seria (see page 138). There the return of the opening music — A in the A B A form — told us that the dramatic situation was just where it had been when the aria started. But at the end of a Classical ensemble, the drama has moved ahead by one notch or more. The music, too, has moved on to something different. The Baroque aria was essentially a static number, the Classical ensemble a dynamic one. The ensemble transformed opera into a much more dramatic genre than had been possible within the Baroque aesthetic.