[1] Advocated mainly by Unionists and loyalists (but also notably supported by one Communist party), who used it as a basis for opposing Home Rule and, later, to justify the partition of Ireland, it has been strongly criticised by Irish nationalists such as John Redmond (who stated that "'the two nation theory' is to us an abomination and a blasphemy"),[2] Éamon de Valera,[3] Seán Lemass[4] and Douglas Gageby.
It was also advocated by the Tory writer W. F. Moneypenny in The Two Irish Nations: An Essay on Home Rule (1913), and was later taken up by the British Conservative politician Bonar Law.
[6] It was advanced in 1907 by the future Supreme Court judge and Sinn Féin Republican TD Arthur Clery in his book The Idea of a Nation.
[10] This led to their formation of the Workers' Association for the Democratic Settlement of the National Conflict in Ireland, in an attempt to draw the left to a non-nationalist position.
[15] In a 1971 speech, Tomás Mac Giolla of Official Sinn Féin condemned O'Brien, Fennell and B&ICO's "two nations theories" as a capitulation to "British imperialism".