Despite efforts to nail down its true being, to define its causes, its significance and its parameters, ‘idiocy’ has remained elusive. John Charles Bucknill admitted in 1873 that, notwithstanding his confidence that he did ‘know what an idiot is’, a definition might be difficult to render all the same. Forty years later, with the Mental Deficiency Act 1913, idiocy was subordinated under the newer banner of ‘mental deficiency’, and while the concepts designated by this new term may have seen their formal legal and medical status solidified thanks to both the Act itself and the enthusiasm of its supporters, in reality these notions remained as slippery, as contentious and as challenging to define as the ‘idiocy’ described by Bucknill. Consequently, these newer notions of mental deficiency did not pass unchallenged. ‘A man is not an imbecile if only a Eugenist thinks so’, G. K. Chesterton argued in his 1922 critique Eugenics and Other Evils: