The development of the concept of a “Great Year” in W. B. Yeats's thought culminated in his most macrocosmic application of the symbolism in A Vision. While the concept has its roots technically in the development of the “World Diagram” in the Automatic Script and the consideration of the Wheel as twelve cycles (YVP1460–61; May 26, 1918), the “Great Year” evolved into a major idea through voluminous reading of various sources, ancient and modern, Asian and European, “respectable” and frankly nonsensical. While Yeats may have begun by regarding the concept as being of Near Eastern origin, he later understood its preferred form—measured by the “precession of the equinoxes” rather than by “alignment of the planets”—as entirely Greek in origin. That said, his later reading of sources also induced him to interpret Hindu thought as incorporating earlier Greek models of the Great Year, as found in Plato's Republicand the pre–Socratic philosophers, with multiple reincarnations through the duration of this period being an element of both Neoplatonic tradition and Hindu theology. Ultimately, he came to understand the role of his discarnate Daimons, as emissaries of the Thirteenth Cone— his closest approximation to an absolute deity—to involve the creation of new illuminations and changes within history, and this understanding was itself a result of the most important and comprehensive of his secondary sources, Pierre Duhem's Systemè du monde: théories cosmologiques de Platon à Copernic(1913–17). Therefore, we will see how Yeats was able to integrate the cycle of the individual soul into the changes and fluctuations of a world soul informing history itself.

Various scholars have discussed the cycles of history in Yeats's work, including Daniel Albright and Brian Arkins, who have posited different illuminations to the religious era preceding the birth of Christ, while Elizabeth Cullingford has examined the relation of Yeats's cycles to his interest in Vico and Hegel. More recently, Colin McDowell has considered the role of astrological conjunctions in governing the same illuminations, while Neil Mann has discussed the role of the Principlesin creating “influxes” at the same points of illumination throughout the months of the Great Year.