GoalsBy extending the analysis of a case identified by Ludwig Binswanger, the Jürg Zünd case, using a philosophical reading inspired by phenomenology, we strive to show that the patient – this is what gives meaning to his disorder – attempts to display the relevance (failure of reason) as well as the limits (reason remains operative) of a doctrine that was made familiar to him by his psychiatrist: existential analysis, notably its representation of space and language. This aims to illustrate the dangers posed by too insistent a dialogue between patient and caregiver when this patient is associated with diagnosis and therapy. Finally, it is a question of better marking the remaining gap between the practical field and the experiential field. The patient has renounced the rationality of her actions but continues to subscribe to that of her experience, the only means of “proof” remaining to her. MethodExtend the psychiatrist's analysis by establishing a correspondence between the symptoms of the illness and the validations/refutations of this same analysis. The main danger of the analysis carried out here is a hyper-rationalization of mental disorder, but if, in the mental disorder, no element of reason remains, no psychiatry can see the light of day either. It is, however, clear that the simple failure of reason cannot be enough to put the scientific exploitation of mental disorder into perspective. We can therefore only follow the author in his frequent references to the fundamental texts of phenomenology. We could say that our analysis is experimental in nature. ResultsAn in-depth analysis of the case shows that there is indeed a link between the patient's system of attitude and behavior and a desire to test the relevance of the phenomenological analysis applied by the caregiver to the patient. DiscussionIn the third Critique, known as the Faculty of Judgment, Kant strives to restore to a reason invalidated in its pure use a path, a field of sensitive expression that, spanning understanding and language, allows this reason to “say itself”, but this behavior is in turn struck by impotence, due to its antinomic structure. Only the body, left out of Kantian analysis, allows reason to find its balance because it is already in itself penetrated, corseted, steeped in reason, but also, by the same token, crushed by this reason, a reason which, by overwhelming the only means of expression that remains to it, overinvests this body and makes itself inaudible again. It will therefore be necessary to return the body to itself, free it from the influence of reason, reify it and, at the same time, allow to reappear what, perhaps, remains in the man of reason: madness, weak reason inhabiting a weakened body. To contradict reason is to speak it out loud, in the experience of its almost although never quite definitive loss, suspended as it is on its own memory. From being the object of clinical inquiry, madness thus becomes its criterion. It establishes its own regime of proof, proof, which, of course, cannot be administered by means of language that is now disqualified. ConclusionMadness has its say in the failure of reason, a failure already thwarted by the disabling examination to which it has been subjected by the Kantian-inspired critical doctrine, which strives to “reason” a reason that exceeds its rights.