What is the main role of the "subject" in a fugue?

The primary role of the "subject" in a fugue is to serve as a melodic foundation. In fugue composition, the subject is a main theme that is introduced at the beginning and is subsequently developed throughout the piece. This theme typically has distinct and recognizable characteristics that anchor the harmonic and textural development of the music.

As the fugue unfolds, the subject is imitated and presented in various keys, but it always retains its melodic identity, which ties the entire composition together. This foundation supports the intricate interplay of voices and counterpoint that are fundamental to the fugue structure, allowing listeners to appreciate the complexity of melodic development while maintaining a sense of cohesiveness based on the initial subject.

While rhythmic stability, dual melodies, and tension are important components in music, they do not encapsulate the defining characteristic of the subject in a fugue, which is fundamentally about creating a strong melodic identity that guides the composition.