Yeats's poetry deepened as he grew older. In the verse of his middle and late years he renounced his early transcendentalism; his poetry became stronger, more physical and realistic. A recurring theme is the polarity between extremes such as the physical and the spiritual, the real and the imagined. Memorable poems from this period include "The Second Coming,""The Tower," and "Sailing to Byzantium." Yeats initiated his second period in such volumes as In the Seven Woods (1903) and The Green Helmet and Other Poems (1910). In 1917 he married Bertha Georgiana Hyde-Lees (known as Georgie or George), and his occultism was encouraged by his wife's automatic writing. His prose work A Vision (1937; privately printed 1926) is the basis of much of his poetry in The Wild Swans at Coole (1917) and Four Plays for Dancers (1921).
Yeats ultimately became a respected public figure, a member (1922–28) of the Irish senate, and winner of the 1923 Nobel Prize in Literature. Some of his best work was his last, The Tower (1928) and Last Poems (1940). All of Yeats's work shows interesting and important revisions from earlier to later versions (see The Variorum Edition of his poems, ed. by Peter Allt and Russell R. Alspach, 1957).