Final answer:
The couplet in an English sonnet serves as a conclusion, summation, or a twist to the sonnet's theme. It underscores the volta, marking a shift in tone or argument, and due to its brevity, it leaves a memorable impact on the reader.
Step-by-step explanation:
The couplet at the end of an English sonnet, often a Shakespearian sonnet, serves a significant purpose. This pair of rhyming lines typically provide a conclusion, summation, or a twist to the sonnet's theme. Within the structure of the sonnet, which includes an octave (eight lines) followed by a sestet (six lines), the couplet comes after the sestet and is marked by its distinctive rhyme scheme, usually GG. For example, in Shakespeare's Sonnet 18, the couplet provides a resolution to the poem's meditation on beauty and immortality.
Moreover, the use of the couplet can underscore a shift in tone or argument in the poem, often referred to as the volta. The volta is a rhetorical turn that shifts from the exposition of the poem to the resolution or conclusion. The couplet's concise form helps to leave a memorable impact and encapsulates the essence of the entire sonnet.