In the friendly contention between philosophers and scientists as to who can best do philosophy of science, Arturo Rosenblueth sides with his own colleagues the scientists, who have a surer grasp of the concepts and methods used in science. He makes a persuasive case, less by exhortation than by example, in this important book. The author is both a scientific generalist and a specialist, and the two aspects together serve to guide his philosophic approach. As a generalist, he organized a seminar on scientific method in the 1930s, as a student and later a collaborator of Walter B. Cannon at the Harvard Medical School, to discuss these questions with exponents of many disciplines and to see them whole. Norbert Wiener, a member of the group, has written about the influence of Dr. Rosenblueth on his formulation of cybernetics, a notable scientific synthesis embracing animal and machine. In his book, Rosenblueth continues his search for scientific universals. As a specialist, the author is a neurophysiologist. He is thereby an experimental philosopher, for this is the field most likely to provide hard answers to the central questions of perception, sensation, volition, and the nature of human knowledge. A nonneurological epistemology can be only impressionistic, and in order to allow the lay reader to follow the later discussions, the book reviews the present state of the neurological sciences, including the speculations on intrinsic uncertainties and indeterminacies, and neural events at the quantum level. Proceeding from a nonbehavioral approach, Rosenblueth regards mental experiences as central and probes into their relationship with physical events in the brain and their link with external reality. He concludes that all that can be directly apprehended about the material universe is what can be coded into afferent nerve impulses and that these can be coded only to transmit information on the structureof spatiotemporal events. Other properties that we ascribe to the material universe are mental in character. This raises the ancient question of the intersection of the material and mental realms, or the duality of brain and mind. After reviewing the writings of Russell, Eddington, and Fiegl on this problem, Rosenblueth proposes a modified dualism in which mental events and the material universe (including the brain) coexist with a measure of independence. Although sensations are the end result of a causal chain that begins with material events, conscious sensations and volitions are not themselves links in a causal chain that in turn influences or changes the material universe. Nevertheless, each mental event can be paired with a neurophysiological correlatethat, being physical, can interact causally with other parts of the material universe. Brain and mind function in parallel—on separate levels of reality that are in constant relation to each other but that do not intersect.