Psychological and psychiatric conceptions of thinking are pre-scientific to a considerable extent. Descartes' separation of 'body' and 'mental phenomena' as independent aspects of reality as a metaphysical construction, is incompatible with modern neurophysiology and neuropsychology. The 'fallacy of misplaced concreteness' (Whitehead), i.e. the mistake of considering ferms for relations and abstractions (thought, volition, ego, consciousness, etc.) as concrete realities is general in psychology and psychiatry. Psychological and philosophical sensualism is incompatible with modern neurophysiology. Locke's 'reflection', compared by this philosopher with a sense organ directed to inner experience is a primitive connotation. Ego is a psychological construct. James, Wundt a.o. regarded consciousness as the last vestige of the mysterious psyche, or soul, which have been rejected by philosophy and scientific psychology. The term consciousness is used for a variety of phenomena. In the field of psychology three main connotations must be distinguished. (I) Vigilance (Head, Russell, Brain) is the degree of intensity of reagibility, from coma to optima[ 'consciousness'. The term confronts us with many theoretical and practical problems. A relation between vigilance and the reticular formation exists. Vigilance is a biological concept. (2) Umweltreactions, such as those of lower animals, show a variety of seemingly intelligent possibilities. They have, however, their ecological-biological basis, and do not allow for a wide scala of adaptations but only for some conditioned reflexes. They do not require a complicated cortex, and may depend on the hippocampus system. The Umweltreactions are quite different from vigilance. (3) Consciousness as awareness of facts and the content of mental phenomena is a different concept again. It is to be regarded, to a considerable degree, as a pre-scientific philosophical construct. Men as self-domesticated homo faber and homo loquens choosing in the fields of 'men tal' images, tools and language, is a choosing animal. Vigilance, Umwelt reactions and choice reactions applying tools and language are entirely different neuropsychological phenomena; to apply the term 'consciousness' indiscriminately to all of them gives rise to misunderstandings. Neurology and neuropsychology help us to conquer this naive philosophy and classical psychology. They enable us to reject Cartesian and Lockian conceptions and metaphysics. Terms like the 'conscious' — not to mention the 'unconscious' — are verbal constructions devoid of any psychological content.