According to intellectual historian Jan E. Goldstein, the initial introduction of idée fixe as a medical term occurred around 1812 in connection with monomania.
[1] The French psychiatrist Jean-Étienne Dominique Esquirol considered an idée fixe – in other words an unhealthy fixation on a single object – to be the principal symptom of monomania.
[2] The term idée fixe had already seeped from psychiatric discourse into literary language before Hector Berlioz employed it in a musical context[3] in his programmatic Symphonie fantastique (subtitled Episode in the Life of an Artist...) of 1830 to denote a recurring melodic theme that references the composer's own romantic obsession (or erotomania) with the actress Harriet Smithson.
[2] Especially around the 1820s and 1830s, the concepts of idée fixe and monomania became firmly associated with the Romantic movement in literature, and fixated protagonists feature in a variety of contemporary novels and plays, ranging from the serious to the almost humorous.
[2] As originally employed in the nineteenth and early twentieth centuries,[4][5] idée fixe described a more specific condition with respect to monomania (a term denoting a wider range of pathologies that did not stem only from a single fixation).
[8] According to Goldstein, the original medical diagnosis of monomania "denoted an idée fixe, a single pathological preoccupation in an otherwise sound mind.
[4] The further historical evolution of idée fixe was much entangled with the introduction of psychologists into legal matters such as the insanity defense, and is found in a number of texts.