Scholars and critics of English literature have regarded Coleridge as a major figure. In his 1927 book "The Road to Xanadu", John Livingston Lowes used Coleridge's poetry, especially "Kubla Khan", to study the working of the human imagination. Critics have argued about the role that opium addiction played in the poet's life and work. In his 1971 book "Coleridge, the Damaged Archangel", Norman Furman showed that Coleridge was guilty of plagiarism in many of his later works. His opium addiction may have left Coleridge unable to tell when he was repeating the work of other writers that he had read.