What term describes an exact transposition of the subject in a fugue?

The term that describes an exact transposition of the subject in a fugue is known as a "real answer." A "real answer" occurs when the subject is represented at a different pitch level, but it maintains the same intervallic relationships as the original subject. This is a crucial aspect of fugal writing, where the melodic and harmonic integrity of the subject is preserved even as it is altered in pitch.

In contrast, a "modified answer" may vary the intervals of the subject or include embellishments, rather than preserving them exactly as a real answer does. "Counterpoint" refers to the technique of combining different melodic lines in a musically harmonious way, while "retrograde" means to present the subject or a musical phrase backward, which does not pertain to transposing the subject at a different pitch.

Thus, the correct term for an exact transposition of the subject in a fugue is indeed the "real answer."