What marks the end of the exposition in a fugue?

The end of the exposition in a fugue is signified by a cadence. In the structure of a fugue, the exposition is the section where the main theme, or subject, is introduced in each of the voices. As each voice enters with the subject, it typically concludes with a strong harmonic resolution, known as a cadence. This cadence serves as a structural marker, indicating that the exposition has reached its completion and that the piece is transitioning to the next section, which could be an episode or development where the material is varied and explored further.

The cadence's function as a closure is crucial because it provides a sense of completion and allows listeners to discern that the thematic material has been fully presented before moving on to the subsequent sections of the fugue. In contrast, elements like the introduction of a countersubject or the use of stretto may occur within the exposition but do not denote its conclusion. The transition to an episode also typically follows the cadence, which confirms that the exposition has ended. Thus, the cadence is essential in defining the end of the exposition in fugues.