There is a category of literature, not yet officially recognised, consisting of mad books. I have been interested in this genre for some time and am in the process of compiling a canon of such things. Mad books are by no means bad books; some, such as William Hazlitt’s Liber Amoris – a feverish account of his sexual obsession with Sarah Walker, the landlord’s daughter, narrated through recollected conversations between a romantic hero identified as ‘H’ and a rejecting woman referred to as ‘S’ – are better than many sane books. Nor are mad books necessarily about madness or written in that state: many a writer of sound mind has produced a mad book. In fact, the existence of the rogue mad book in an author’s otherwise stable oeuvre can seal his or her greatness.