The poem's tone shifts in the ninth line, where the speaker begins with "Yet." This word indicates a contrast or a concession to the previous eight lines, where the speaker laments his absence from his beloved and compares it to a bleak winter. The ninth line marks the beginning of the third quatrain, where the speaker reveals that his time away was summer's time, full of abundance and fertility. However, he still feels unhappy and hopeless, as if he had lost his spouse or children. He explains that his joy depends on his beloved's presence, and everything seems dull and lifeless without him. The tone in this quatrain is less sorrowful than the first two but still melancholic and longing. The tone shifts again in the final couplet, where the speaker uses a conditional clause, "if they sing," to imagine a scenario where the birds are not mute. He concludes that even if they sing, their cheer is so dull that the leaves look pale, fearing the winter's near. The tone in this couplet is more pessimistic and resigned than the previous quatrain, as the speaker suggests that there is no hope or happiness in his absence. The poem is a Shakespearean sonnet, usually with a volta or a turn before the final couplet. However, this poem has two voltas, one in the ninth line and one in the thirteenth line, creating a more complex and nuanced expression of the speaker's emotions.