The Category Error in Psychiatry identifies a foundational conceptual mistake at the heart of modern psychiatric theory: the treatment of symptom clusters as if they were the underlying structure of mental suffering. This paper argues that symptom‑based categories are late‑stage projections of deeper relational distortions, not generative mechanisms. By introducing three structural invariants—orientation, boundary coherence, and information flow—the paper reframes psychiatric phenomena in terms of the relational conditions that make coherent mental life possible. Structural distortions in these invariants produce the recurring patterns that psychiatry interprets as discrete disorders and comorbidities.The result is a discipline‑neutral, non‑clinical framework that explains why symptom clusters repeat across individuals, why comorbidity is pervasive, and why existing diagnostic categories fail to converge. Rather than proposing treatments or diagnostic alternatives, the paper offers a conceptual foundation that may help unify research across psychiatry, psychology, cognitive science, and developmental theory. It is written from the perspective of a student developing a structural ontology of mental life, with the aim of clarifying the generative mechanisms behind recognizable patterns of suffering.