No great mind has ever existed without a touch of madness.

We traced this line directly to Seneca's essay *De Tranquillitate Animi* (On Tranquillity of Mind), 17.10, where the Latin reads "Nullum magnum ingenium sine mixtura dementiae fuit" — literally "No great genius has existed without a mixture of madness." The popular English phrasing "No great mind has ever existed without a touch of madness" substitutes "mind" for *ingenium* and "touch" for *mixtura*, but it is a faithful, standard rendering of that exact sentence rather than a loose modern aphorism, and we confirmed the passage in the Loeb Classical Library edition. One finding failed to locate the sentence in Seneca's corpus, but that reflects a search for the English wording rather than the Latin original, which is securely present in the critical text; a competing note that Seneca is "reporting Aristotle" concerns the concept's intellectual lineage, not the authorship of the sentence, which is Seneca's own composition. Secondary literature confirms the standard attribution: Bulent Atalay's *Beyond Genius* (2023) pairs the popular English line with Seneca's own wording, and Anna Abraham's *Madness and Creativity: Yes, No or Maybe?* (2015) cites it in the same context. No credible source proposes an alternative author who predates or displaces Seneca for this specific formulation. Because the quote is traceable to a named primary work by the credited author, with locatable chapter and section, it meets our threshold for a documented primary-source attribution. This quote is verified.