How is mind related to matter? This ancient question in philosophy is rapidly becoming a core problem in science, perhaps the most important of all because it probes the essential nature of man himself. The origin of the problem is a conflict between the mechanical conception of human beings that arises from the precepts of classical physical theory and the very different idea that arises from our intuition: the former reduces each of us to an automaton, while the latter allows our thoughts to guide our actions. The dominant contemporary approaches to the problem attempt to resolve this conflict by clinging to the classical concepts, and trying to explain away our misleading intuition. But a detailed argument given here shows why, in a scientific approach to this problem, it is necessary to use the more basic principles of quantum physics, which bring the observer into the dynamics, rather than to accept classical precepts that are profoundly incorrect precisely at the crucial point of the role of human consciousness in the dynamics of human brains.