 Clery advocated partition on the basis of a two nation theory, first advanced in 1904–05 (possibly in response to William O'Brien's advocacy of securing Home Rule through compromise with moderate Unionists).Several of his articles on the subject were reprinted in his 1907 essay collection, "The Idea of a Nation".Clery derived this unusual view for a nationalist from several motives, including a belief that arguments for Irish nationalists' right to self-determination could be used to justify Ulster Unionists' right to secede from Ireland, fear that it might be impossible to obtain Home Rule unless Ulster were excluded, and distaste for both Ulster Protestants and Ulster Catholics, whom he saw as deplorably anglicised.