What is a fugue primarily characterized by?

A fugue is primarily characterized by thematic development through imitative counterpoint. This form of musical composition involves a single theme (or subject) that is introduced by one voice and then echoed by other voices in succession. The key feature is this imitative counterpoint, where the thematic material is developed and varied, allowing for intricate polyphonic textures.

In a fugue, the subject is often subjected to various transformations, such as inversion, retrograde, and augmentation, while remaining recognizable. This complex interplay between voices creates a rich tapestry of sound that showcases both the composer’s ingenuity and the performers' skills. The development of the main theme in this manner is what sets the fugue apart from other musical forms.

The other options do not accurately reflect the essence of a fugue. The use of multiple soloists does not define the structure or style inherent to a fugue, since fugues can be written for any number of voices, including a single instrument. Similarly, while orchestration can play a role in various types of music, fugues specifically focus on counterpoint rather than orchestral accompaniment. Furthermore, static harmonies are not a characteristic of fugues, as they typically exhibit a dynamic harmonic progression that complements the thematic development.