Poets use symbols because they have realized that our common language is inaccurate in describing the inner reality.
In A Vision, Yeats presents an elaborate symbolic pattern which he applies not only to history, but also to individual lives. One of his basic symbols is a pair of interpenetrating whirling cones or "gyres" signifying the world of change that move within a sphere emblematic eternity. The gyres, with their points at the bases of each other, represent the oppositions and reciprocity of human existence; one expands as the other diminishes. The two gyres stand for two contrasting forces―the primary or objective and the antithetical or subjective. There is a state of perpetual conflict between the gyres The “sphere” is the symbol of perfection, "Unity of Being". These symbols of sphere and gyres are equivalent to another set of symbols, in which a circle or "The Great Wheel" is marked off into "phase" that correspond to the waxing and waning of the moon. There are twenty eight such phases, with varying degrees of moonlight and darkness. They can be applied to human personality and to the incarnations of the soul. Each quarter of "The Great
Wheel" represents a completely different character. The first quarter is identified with the body, the second with the heart, the third with the mind, and the fourth with the soul. The result of the mixture of these principles at any one phase must be measured in terms of "Four Faculties," which usually are at odds with one another. As "Four Faculties" with living here, "Four Principles" apply to the life after death. The Principles find their Unity in the Celestial Body, man's archetype in Heaven.