Yeats uses figurative language as an evocation of the mythology that often serves as the source of his themes or as support for the themes that concern him. In "The Circus Animals' Desertion," his own works are likened to circus animals being trained to do tricks and to convey something to the public, and in that work he talks explicitly about his use of myth and metaphor. The metaphors may derive from Christian symbolism as in "The Second Coming" or "The Magi," or it may derive from the mythic world of Cuchulain and other Irish heroes. In "September 1913," Yeats uses an action on that date when Sir Hugh Lane offered a collection of valuable paintings to Dublin if the city would build a gallery for them, a gift that was rejected, as a metaphor for the loss of Ireland's heroic past.
The use of such extended metaphors serves several purposes. It holds a poem together around a central image, for one thing, and the power of the poem will depend on the cogency of the image and the way the poet relates all that he discusses to that central image. The image helps the reader follow the argument, providing a central concept that can help explain what the poet means and that helps unify the theme. The central metaphor also serves as a gateway to myth, itself based on primal imagery and archetypes. The metaphor contributes to the use of figurative language and so to the ability of the poet to compress complex ideas into fewer words.
Yeats uses a different sort of mythology and symbolism in his poem "The Second Coming," in this case Christian mythology. In the opening stanza, the poet set up an image and carries it through to lead to another. This poem is one in which one extended metaphor dissolves into a second. The first is an image taken from falconry, and the second is an image which uses the idea of falconry, with the controller as a god at the center trying to give commands to the falcon, as a reflection of the Chris