The general relationship of A Vision to "The Second Coming" has been accepted by most critics, yet the elusive nature of Yeats's imagery has prompted varying interpretations of the poem. Many scholars have focused on its political character and especially on the sphinx-like beast of the poem's second half, seeing it as representative of the general forces of violence and anarchy, or more specifically of the Russian Revolution, World War I, the Irish Civil War of 1916, Fascism, or communism. Such views typically emphasize the horrific and ominous nature of the beast, and associate its appearance with the decline of western civilization. Critics who have used A Vision extensively in their interpretations of the poem, however, have occasionally noted that the sphinx is not necessarily intended as a negative image—and that Yeats himself was not displeased to witness what he viewed as the close of the Christian era. Commentators have also seen "The Second Coming" in the context of other poems by Yeats that elicit similar or parallel themes, such as "Leda and the Swan" and "A Prayer for My Daughter." Additional areas of critical interest concerning the work include study of the symbolic nature of the falcon, exploration of the lengthy process of revision undertaken by Yeats, and consideration of the poet's ironic use of religious allusion in the poem. Others critics have also observed significant influences on the work, which contains echoes of Percy Shelley's Prometheus Unbound, and have examined its philosophical underpinnings, particularly in relation to the conception of alternating cycles of human history proposed by Friedrich Nietzsche. Overall, "The Second Coming" has been well-received as one of the most evocative visionary lyric poems of the twentieth-century and widely praised for its technical excellence and extensive symbolic resonance.