What defines a symphony's structure?

A symphony is typically characterized by its four-movement structure, which allows for a dynamic exploration of various musical forms, tempos, and styles. This standard structure often includes an opening movement in sonata form, a slow second movement, a dance-like third movement (such as a minuet or scherzo), and a final movement that is often lively and upbeat, frequently employing rondo or sonata-allegro form. Each movement serves a different purpose, contributing to the overall emotional and thematic development of the work, providing both contrast and cohesion throughout the entire piece.

The other options do not align with the traditional definition of a symphony. For instance, two movements with vocal accompaniment or three movements predominantly for strings do not represent the standard symphonic form. A single movement featuring one instrument is indicative of a concerto rather than a symphony, which is meant to encompass a larger orchestral palette. Thus, the four-movement structure is definitive in understanding what constitutes a symphony.