However it appears to be in vain: approaching hoof beats of his ghostly father returning to the bridal bed signal that no spirits have left the place, and the grim cycle begins again... Yeats had been strongly influenced by Japanese Noh theatre in the later years of his life (via Ezra Pound), and Yeats' use of the spirits of the Old Man's parents as a metaphor for the family's decline and of death and rebirth is Noh's clearest influence on the drama.
As he wrote Purgatory he admitted in a letter that the scenario troubled him: I have a one-act play in my head, a scene of tragic intensity...
Several critics[2] noted the discomforting implications of reading, as Yeats himself suggested, the Old Man's murder of the Boy as an exercise in eugenics and as such perceive the conclusion as somewhat tendentious.
T. S. Eliot took a similar line, attacking the play's title from a Christian perspective, arguing that murder does not sit with any notion of purgation.
[3][4] Ed Di Lello composed, orchestrated, conducted and staged Purgatory as an opera on a double bill with Yeats' The Cat and the Moon produced by Philip Meister and Maurice Edwards at The Cubiculo in New York City in March 1974.