In Western classical music theory, what is the main recurring theme of a fugue called?

Introduction / Context:
A fugue is a highly structured form in Western classical music, especially prominent in the works of composers like Johann Sebastian Bach. It features a main musical idea that is introduced and then developed through imitation and variation across multiple voices. This question asks for the technical term used in music theory for that principal melodic idea that appears repeatedly in a fugue.

Given Data / Assumptions:

• The musical form under discussion is a fugue.
• We are interested in the main recurring theme of the fugue.
• Options include several music-theory terms: subject, melody, episode, and exposition.
• We assume a basic familiarity with classical music terminology.

Concept / Approach:
In a fugue, the main theme is known specifically as the “subject.” This subject is first presented by one voice and then successively imitated by other voices, often at different pitch levels. While “melody” is a generic term that can describe any tune, “subject” is the precise technical term for the principal theme of a fugue. “Episode” refers to sections where the subject is absent or fragmented, and “exposition” is the introductory section where the subject is first fully presented by all voices in turn.

Step-by-Step Solution:
Step 1: Recall the definition of a fugue: a contrapuntal composition based on a central theme introduced successively in different voices. Step 2: Remember that the main theme of the fugue is called the “subject,” not just a generic melody. Step 3: Recognize that although every subject is a melody, not every melody in the piece is the subject; only the principal recurring idea is given this name. Step 4: Understand that the “exposition” is the section where the subject is introduced in all voices, so it cannot itself be the name of the theme. Step 5: Confirm that “episode” labels the connecting or developmental passages between subject entries, not the main theme itself. Step 6: Based on these definitions, choose “Subject” as the correct technical term for the main recurring theme of a fugue.

Verification / Alternative check:
Any standard music theory textbook or resource on Baroque counterpoint will define the parts of a fugue in detail. You will find that the principal recurring idea is always referred to as the “subject,” with its accompanying answer, countersubject, and various entries in different voices. This consistent usage across theory courses and textbooks confirms that “Subject” is the correct answer, while the other terms describe different structural elements of the fugue.

Why Other Options Are Wrong:
“Melody” is too general a term and does not capture the specific function of the main fugue theme. “Episode” denotes a passage where the subject is absent or only partially present, used to provide contrast and development. “Exposition” is the initial section of the fugue where the subject is presented in each voice; it is a structural section, not the theme itself. Therefore, none of these alternatives correctly names the main recurring theme of a fugue.

Common Pitfalls:
Students often confuse “subject” with “melody” because the subject is indeed a melodic line. Another common error is mixing up the word “exposition” with “subject,” since the exposition is the first place where all voices present the subject. Without careful study of terminology, one might also assume that “episode” refers to the theme because it sounds like a significant event. Understanding that music theory uses very specific labels for forms like fugues helps prevent these mistakes.

Final Answer:
The correct term is Subject, which is the technical name for the main recurring theme in a fugue in Western classical music theory.