Ralph Waldo Emerson, Robert Ernest Spiller, Alfred Riggs Ferguson, Joseph Slater, Jean Ferguson Carr (1971). “The Collected Works of Ralph Waldo Emerson: Nature, addresses, and lectures”, p.58, Harvard University Press
T. S. Eliot (1986). “The Use of Poetry and the Use of Criticism: Studies in the Relation of Criticism to Poetry in England”, p.111, Harvard University Press
John Milton (1824). “The Poetical Works of John Milton: With Notes of Various Authors, Principally from the Editions of Thomas Newton, Charles Dunster and Thomas Warton ; to which is Prefixed Newton's Life of Milton”, p.40