Final answer:
In Sonnet 18 by William Shakespeare, Time serves to illustrate the temporary nature of beauty, contrasting it with the everlasting nature of the beloved's beauty as immortalized in the speaker's poetry.
Step-by-step explanation:
In William Shakespeare's Sonnet 18, the function of “Time” is best described as conveying the impermanence of physical beauty compared to the enduring nature of the beloved's loveliness as immortalized through poetry. Option (a) “The speaker declares that his beloved’s loveliness will live on forever through his poetry, unlike the short-lived summer season” is the one that most accurately captures this sentiment. In particular, the poem contrasts the temporary and fluctuating nature of a summer's day with the perpetual beauty of the speaker's beloved, which is eternalized in verse. Shakespeare creates a dichotomy between the transient aspects of nature and the lasting impact of literary expression.
Thus, through poetic form, the speaker ensures that while physical beauty is subject to the whims of time and nature, the beauty of the beloved will endure “so long as men can breathe or eyes can see.” This theme of the enduring power of art to capture and preserve beauty is a common one in literature and is vividly portrayed in this sonnet. The poet asserts that as long as the poem is read, the beloved's beauty and memory will persist, transcending the limits of Time.