Time
Keats frequently alludes to the passing of time through the characters and images that appear in the poem. The abundant landscape is juxtaposed by imagery that symbolizes exhaustion: vines and tree branches are heavy with summer's harvest, but the speaker forsees the cider press squeezing 'the last oozings' of the season's fruits. In the final stanza, Keats uses language directly associated with death.
Nature
Throughout the poem, Keats utilizes figures from the natural world to ground the tensions between life and death. Summer's hard work is evident in the abundant landscape, but the speaker foresees the moment at which all of Nature's labor will be used up and lost. While the buzzing bees and blooming flowers of the first stanza symbolize the endurance of life, the 'barred clouds' and "wailful choir" of gnats refer to the beginning of the end.
Music
Keats uses the metaphor of music to distinguish between the character of the seasons. Autumn's music, he realizes, may not have the same tune as spring's, but it is lovely nonetheless. Their songs are too different for a proper comparison. Instead, he recognizes that he must take each on their own terms and accept this difference with grace, if not joy.
