Lees, Francis Noel (1967) "The Keys Are at the Palace: A Note on Criticism and Biography" pp. 135-149 In Damon, Philip (editor) (1967) Literary Criticism and Historical Understanding: Selected Papers from the English Institute Columbia University Press, New York, OCLC390148
Discussed extensively in Frye, Herman Northrop (1947) Fearful Symmetry: A Study of William Blake Princeton University Press, Princeton, New Jersey, page 326 and following, OCLC560970612