William Butler Yeats, Richard J. Finneran, George Bornstein (2007). “The Collected Works of W.B. Yeats Volume IV: Early Essays”, p.8, Simon and Schuster
"Conrad Aiken, The Art of Poetry No. 9". Interview with Robert Hunter Wilbur in September 1963, "The Paris Review", www.theparisreview.org. Winter - Spring 1968.