David Hume (1824). “The Philosophical Works of David Hume ... Containing Dialogues Concerning Natural Religion, Essays on the Immortality of the Soul, Suicide ... &c. A New Edition”, p.6
William Butler Yeats, Richard J. Finneran, George Bornstein (2007). “The Collected Works of W.B. Yeats Volume IV: Early Essays”, p.88, Simon and Schuster