Neil Mann interprets:
Since it affects the poetry more obviously and more directly than almost any other part of the System, the view of history proposed in A Vision has received more critical attention than any other area, not all of it entirely accurate. The basic principles are, however, relatively easy to grasp, and Yeats himself noted that the section treating history, ‘Dove or Swan’ (AV A Book III and AV B Book V), was among the more accessible parts of A Vision.
The title ‘Dove or Swan’ alludes to a particularly potent yoking of ideas through symbol. The Archangel Gabriel’s annunciation to the Virgin Mary is often accompanied in art by a descending dove to symbolise the angel’s message that she would conceive a child: ‘The Holy Ghost shall come upon thee, and the power of the Highest shall overshadow thee: therefore also that holy thing which shall be born of thee shall be called the Son of God’ (Luke 1:35). The tradition of representing the Holy Ghost by a dove derives from the Gospel account of Jesus’ baptism: ‘And Jesus, when he was baptized, went up straightway out of the water: and, lo, the heavens were opened unto him, and he saw the Spirit of God descending like a dove, and lighting upon him: And lo a voice from heaven, saying, This is my beloved Son, in whom I am well pleased’ (Matthew 3:16-17). Yeats imaginatively contrasts the Annunciation to Mary and the divine conception, symbolised by the hovering dove, with an alternative annunciation: Leda’s rape by the god Zeus in the form of a swan, which led to the conception of Castor and Pollux, Helen of Troy and Clytemnestra. Yeats sets these two annunciations up against each other: in each one the bird symbolises the irrational and supernatural irruption of the divine into the human order, but one is a violent act which produces war and heroism, while the other is a gentle presence which harbingers peace and sacrifice.
The Christian annunciation inaugurates a ‘primary dispensation looking beyond itself towards a transcendent power’, which ‘is dogmatic, levelling, unifying, feminine, humane, peace its means and end’; the preceding classical annunciation inaugurates ‘an antithetical dispensation’, which ‘obeys imminent [for immanent?] power, is expressive, hierarchical, multiple, masculine, harsh, surgical’ (AV B 263). The cyclical nature of Yeats’s conception means that there will be another antithetical annunciation in the near future, the second coming not of Christ but of His antithetical opposite, the focus of one of Yeats’s most celebrated poems ‘The Second Coming’ (see the Future).
. . . now I know
That twenty centuries of stony sleep
Were vexed to nightmare by a rocking cradle,
And what rough beast, its hour come round at last,
Slouches towards Bethlehem to be born?
Elsewhere, Yeats portrays the antithetical Messiah as Oedipus, ‘an image from Homer’s age’ (AV B 28), who lay down upon the earth and ‘sank down soul and body into the earth. I would have him balance Christ who, crucified standing up, went into the abstract sky soul and body’ (AV B 27):
What if Christ and Oedipus or, to shift the names, Saint Catherine of Genoa and Michael Angelo, are the two scales of a balance, the two butt-ends of a seesaw? What if every two thousand and odd years something happens in the world to make one sacred, the other secular; one wise, the other foolish; one fair, the other foul; one divine, the other devilish? What if there is an arithmetic or geometry that can exactly measure the slope of the balance, the dip of the scale, and so date the coming of that something? Michelangelo Buonarroti
(AV B 28-29) Saint Catherine of Genoa
This cycle, which he suggests here so speculatively, is of course the basis of his view of history. It is not, however, the only cycle involved, and its workings are slightly more involved than this outline indicates.
The paradigm of the gyres and the cycles that they represent applies to every process, including the wider sweep of history. Like the harmonics of a plucked string, many different lengths of cycle co-exist within the overall cycle, each with its distinctive periodicity, so that at any one time each will be at its own stage of progress. Of particular importance within his treatment of the historical process are the cycles of roughly four thousand years, two thousand years and one thousand. An eight-thousand-year cycle exists but stretches too far back into pre-history to be useful, and the cycles of five hundred years and less begin to become too detailed for Yeats’s broad and impressionistic treatment.
Yeats is not alone in discerning a cyclical pattern history, and such cycles are present in several ancient traditions, most notably Hinduism. In modern European tradition, Agrippa’s friend, the Abbot Trithemius, citing ancient precedent, expounded a cyclical series of epochs, governed by the seven planetary archangels, in ‘Concerning the Seven Secondary Intelligences’ (1508; another web-site gives the text), a scheme which was adopted in the twentieth century by Rudolf Steiner. A particularly influential scheme was proposed by Giambattista Vico in The New Science (1725; 3rd ed., 1744; another site’s English comment and Italian text (at present only partial) here), which starts from a scheme of development based on three ages attributed to ancient Egyptian doctrine. A more philosophical and abstract theory appears in G. W. F. Hegel’s Lectures on the Philosophy of World History (1822-1831) and The Philosophy of History (1837; another site’s text), and in the twentieth century the most widely known scheme is probably Oswald Spengler’s in Decline of the West (1918-1922; translated 1926-29; another site’s selections). Though Yeats did not know Spengler’s work when he published the first version of A Vision, he may have had an acquaintance with Vico’s and possibly with Hegel’s, and he studied them all in more depth as he prepared for the second edition, along with Flinders Petrie’s The Revolutions of Civilisation (1911), Hermann Schneider’s The History of World Civilization (translated 1931) and Henry Adams’ The Degradation of the Democratic Dogma (1919) (see AV B 261). More important and significant for him, however, was the astrological tradition of the ‘The Great Year of the Ancients’ (viz AV B Book IV, 243ff.), related to the phenomenon of the precession of the equinoxes, and it is this major cycle that determines the actual lengths of the periods involved.
Read more here.