What is an "answer" in the context of a fugue's structure?

In the context of a fugue's structure, the term "answer" refers specifically to the repetition of the subject in another voice, typically a fourth or fifth away from the original pitch. This is a fundamental aspect of fugal composition, as it demonstrates counterpoint—the interaction between different melodic lines. When a subject (the primary theme) is introduced in one voice, the answer follows in another voice, creating a harmonious dialogue and establishing the thematic material within multiple layers.

The answer is crucial for building the contrapuntal tension and complexity that characterize fugues. It serves to maintain thematic coherence while introducing variation through its transposition. This structural device not only enhances the music's texture but also illustrates the development of ideas within the composition, marking the transition from the exposition phase of the fugue to subsequent developmental sections.