Final answer:
In the exposition of a fugue, when the second voice states the subject, the first voice introduces a contrasting melody called a counterpoint, underscoring the harmonic interplay characteristic of Renaissance music.
Step-by-step explanation:
When the second voice in the exposition of a fugue enters stating the subject, the first voice continues simultaneously, stating a contrasting melody called a counterpoint. This technique is central to the structure of a fugue, emphasizing the interplay between different musical lines that, while independent, are harmonically interrelated. This practice was particularly prominent during the Renaissance period where music sought a richer texture with multiple parts and smoothness between voices was achieved through the use of consonant intervals like thirds, moving beyond the rigid constraints of Medieval music.