Three main strategies for the study of behavior and mentation are examined: behaviorism, mentalism, and psychobiology. Behaviorism is found wanting for eschewing most of the problems that traditional psychology posed but left unsolved. Two kinds of mentalism are distinguished: traditional and cognitivist (or information-theoretic). Both are found wanting for ignoring the nervous system and begging the question, since they postulate the mind instead of explaining it. Only the psychobiological (or neuropsychological) approach, which regards the mind as a collection of brain functions, is found promising for studying that which guides behavior and does the mentation, namely, the brain. It is also shown to have the advantage of promoting the union of psychology with biology and of bridging psychiatry to neurology, neurophysiology, and neurochemistry. It is argued that this approach is the only fully scientific one of the three approaches discussed in the paper.