This paper identifies and analyzes systematic category mistakes that pervade classical and contemporary philosophical debates from antiquity to the present, structuring discussions in ontology, epistemology, philosophy of mind, and ethics. Six fundamental types of category errors are distinguished: ambiguity of central concepts; conflation of descriptive levels; substantive reification of processes; confusion of syntax with semantics; ungrounded metaphysical assumptions; and ontologization of normative values. Through classical and modern examples, it shows how unmarked shifts between logical levels generate theoretical confusion, misleading metaphysical claims, and conceptual puzzles. The diagnosis reveals that many current scientific and philosophical theories revive old category errors in new forms under the guise of exact sciences, particularly in cognitive science, artificial intelligence, and neuroscience. The paper argues for establishing "category hygiene" as a methodological principle that clarifies conceptual distinctions, avoids illegitimate ontological claims, and grounds philosophy more firmly in critical reflection and empirical engagement. This approach aims to revitalize philosophy's critical role by dispelling persistent confusions rather than generating novel metaphysical systems.