The author sketches a literary history of writers affected by mental disturbance, examining how hallucination, monomania, and ecstatic conviction can overlap with creativity and religious enthusiasm. He surveys the difficulty of distinguishing madness from intense genius, proposes a fourfold division into theological, literary, philosophical, and political categories, and offers biographical sketches and etiological reflections. The work highlights that many disorders produce focused delusions alongside otherwise intact reasoning, comments on the rarity and bibliographical interest of such writings, and emphasizes the challenges of defining and delimiting this field of study.