I think that one can find many examples of Yeats employing symbolism throughout his work. Since the question is asking for how it is used, I would focus on the symbols present in my favorite Yeats poem, "The Second Coming." The use of symbolism is profound in trying to evoke a particular mood of the poem. Yeats wishes to bring out the moral, political, ethical, and social confusion of the world that faced consciousness in the wake of World War I and the uncertainty that abounds as a result. When we survey the landscape of this setting, Yeats compels us to do so by rendering symbolic images of a world fraught with fragmentation and doomed by dissolution. The symbolic meaning of "the falcon cannot hear the falconer" or "the centre cannot hold" help to bring out this idea. Yeats' uses symbols to help represent what is happening in Europe and the world of the time. This heightens the impact of the poem for it allows the reader to make connections on both social and personally introspective levels for the symbols apply to both.