In recent linguistic theory and the Minimalist Program in particular, the interface between linguistic and non-linguistic cognition has come to be of critical importance in the study of the nature of the faculty of language. In this regard, Un-Cartesian linguistics has radicalized old ideas about the nature of this interface, according to which the intrusion of language into the brain has reformatted primate cognition, creating a novel neural infrastructure in which human-specific thought can arise and without which it is unavailable. If so, there is no interface between two independent systems of language and thought in humans, and generativity in language and human-specific thought are the same. New evidence for this hypothesis comes from thought disturbances (psychopathologies). Un-Cartesian linguistics predicts that such disturbances must involve language disturbances. I will review recent evidence from my lab testing this prediction in three clinical populations: children and adolescents with autism who do not develop language in any modality, whether in production or in comprehension; patients with formal thought disorder, a symptom of schizophrenia; and patients with Huntington’s disease, an early dementia. It turns out that in all three cases, there is strong evidence that thought disintegration is mirrored in language disintegration, in a way that appears to be independent of non-linguistic neuro-psychological deficits. It is thus potentially key to better understanding these disorders and the connection between language and thought at large.