Use of symbolism in W.B.Yeat's "The Wild Swans at Coole"
First, the question is ambiguous, since the whole collection of poems was called “The Wild Swans at Coole.” Secondly, the question answers itself: the symbolism is used as a symbol. But assuming you mean something like “How do the symbolic elements work toward the poem’s power?” I would venture that two major symbols are at work here: the swans in pairs, and the migratory habits of the flock. “Nine-and-fifty” says that one of the swans has lost its mate since last migration; a reader of Yeats is never far off when remembering Yeats’ love (and loss) of Maude Gonne, and the poem, set in Autumn and written in the Autumn of the poet’s life (he was 54), and speaking of life-long habits (counting the swans, and “all’s changed”), one begins to see the symbolic parallels. If we go further into Yeats’ predilections for bird symbolism (the falcons in their “widening gyre,” for example) and for nostalgic remembrance (“When you are old and gray” is an example ready to hand), we see how the poem works.