The waxing and waning fortnights are not a major part of the symbolism of Yeats’s System, which is dominated rather by the fortnights of greater light and of lesser light. He notes that the movement from ‘Phase 1 to Phase 15 is towards Nature’, while that from ‘Phase 15 to Phase 1 is towards God’ (AV B 104), but otherwise concentrates more on the Quarters and the Tinctures.
He does, however, find some correspondences in Indian thought. In his introduction to The Holy Mountain (1934), he examines the two forms of samadhi or release: Turiya, the samadhi of wakefulness is aware of all levels of being, while Sushupti is the release of unknowing, abstraction into dreamless sleep. He looks to certain passages in the Upanishads, where ‘mention is made of the moon’s bright fortnight, the nights from the new to the full moon, and of the dark fortnight of the moon’s decline’. These suggest that those who are under the waxing half are individual in their devotions and ‘may, if wise, go to the Gods (expressed or symbolised in the senses) and share their long lives’ or even pass out of life, while for the more focused ascetic the ‘bright fortnight’s escape is Turiya’; in contrast, the pious of the waning half follow the crowd and ‘can go to the blessed Ghosts, to the Heaven of their fathers, find what peace can be found between death and birth’ but are denied any escape, though the ascetic may ‘find Sushupti an absorption in God’ (E&I 469-470). Yeats’s imagination makes two groups of associations, ‘in one line Turiya—full moon, mirror-like bright water, Mount Meru; and in the other Sushupti, moonless night, “dazzling darkness”—Mount Girnar’ (E&I 472). The people of the waxing fortnight are clearly associated with the antithetical in Yeats’s reading, though the first half of this is primary in his own System, while the people of the waning fortnight are associated with his primary Tincture, even though the first half of this is antithetical in his System, and his own Phase falls in this fortnight. The shift is crucial in terms of detail, but less important in general principle, and when he considers the astronomical conflict symbolised in Sun and Moon, Yeats wonders whether he is ‘justified in discovering there the conflict between subjectivity and objectivity, between Self and Not-Self, between waking life and dreamless sleep’ (E&I 470).