The sestet may be taken as an excellent example of the manner in which Mozart turned his means of representation to account. We are struck first of all with his power of grouping so as to produce a clear and distinct whole. The effect and appreciation of music depends, like architecture, on symmetry. Even though a strict parallelism of the different component parts may be in all but certain cases inapplicable, yet their symmetry must be always present to the apprehension of the hearers. In the musical drama the characterisation of the situation dominates the construction side by side with the laws of musical form. In the sestet before us Marcellina, Bartolo, and Figaro form a natural group, announcing themselves at once as connected from a musical point of view, Marcellina and Bartolo closely corresponding, Figaro forming the uniting member of the little group. Opposed to them we have the Count and Don Curzio, who also keep together, but with greater freedom of independent movement. Susanna's entry introduces a new element. At first she opposes Figaro, and allies herself to the Count, and we have then two strongly characteristic groups of three persons, each with a construction and {TREATMENT OF THE VOICE PARTS.} (109) movement of its own. The explanation which ensues necessitates the dissolving of the ensemble into a monologue, after which the situation is changed. Susanna goes over to Figaro, Marcellina, and Bartolo, and fresh group is formed, with Susanna as the chief member, though the others do not by any means renounce their independence. Against this concentrated force the discontented minority gives expression to additional energy and resentment, coming to an end in unison. These hints will suffice to show with what a firm mind of the hearers an impression of the perfect freedom of dramatic action, within the limits of strict and simple musical form. The great stress laid upon dramatic reality necessitated in general simple forms and moderate execution in the musical part of the work. In the airs the traditional form of two elaborate movements is only exceptionally employed the cavatina or rondo form being in most cases preferred and treated freely, although with considerable precision the majority of the duets are similar in design, Mozart having usually written over them _duettino, arietta_, But neither confined limits nor dramatic interest have been made a pretext for the neglect of well-constructed, well-rounded form;