Interest in _dream_ and _madness_, conceived as the loss of a world shared with others, and the individual’s entry into a private world governed by a personal logic unrelated to the waking state and to common feeling, recurs in at least three of Kant’s works: _Essay on the Diseases of the Head,_ (1764), _Dreams of a Spirit-Seer_ (1766), and _Anthropology from a Pragmatic Point of View_ (1798). Hegel too, from an early age, showed a strong fascination and a precocious interest (...) in psychopathological matters (states of altered consciousness, prophetic dreams, somnambulism, catalepsy, witchcraft etc.) to which he devoted intriguing reflections in various works from different periods: from the Berne Ms _Philosophy of Subjective Spirit_ (1794/95) to the _Phenomenology _(1807), from the _Philosophical __Propaedeutics_ (1808ff.) to the _Encyclopedia of the Philosophical Sciences_ (1830 3 ). Starting from the remarks of the two philosophers, this paper aims to underline the conceptual links between their thought and that of some renowned psychologists and psychiatrists of the 1800s-1900s (Pinel, Janet, Adler, James, Binswanger, Freud et al.). On the other hand, the paper also seeks to show – within the framework of an idea of _reason_ dating back to Heraclitus (about 544/483 B.C.) – some murky motifs, not always adequately emphasized in the past, found in the figurative and literary works of the late 1700s (e.g. Fuseli’s_ The Nightmare_, Coleridge’s _The Rhyme of the Ancient Mariner_, and, in particular, plate Nr. 43 of the _Caprichos _by Goya, _El sueño de la razón produce monstruos_), where there emerges a «dark side» of psychic activity emblematically described as the cryptic relationship between _dream_ and_ madness._. (shrink)