So long as men can breathe or eyes can see,

So long lives this, and this gives life to thee.

—“Sonnet 18,”
William Shakespeare

In one to two sentences, explain the central idea of the final couplet of the poem.

The final couplet of the poem suggests that as long as there are people who can breathe and see, this poem and the love it portrays will continue to exist and give life to the beloved.

The central idea of the final couplet of Shakespeare's "Sonnet 18" is that as long as people can breathe and see, the poem's subject will live on through the words of the poem, giving the subject eternal life.

The final couplet of "Sonnet 18" emphasizes the timeless nature of the poem's subject's beauty and its ability to grant eternal life through its immortality in the words of the poet.