The eliminative materialism does not approve the explanation of behavior based on mental states. It insists that human behavior should be explained solely based on neuronal phenomena. With the purpose of rejecting the belief in mental states, the supporters of this view call belief in mental states a conventional view which stands against neuroscience. Analyzing the basic principles of eliminative materialism, the present article demonstrates that this view is a kind of ontological monopoly that is incapable of explaining the nature of mind. It is also argued that with the denial of the existence of mental states, there will neither be space for psychology as a scientific applied field of knowledge nor for the key concepts of social sciences. Scientific psychology moves forward with assumption that humans are social beings and this basic assumption which shapes psychology as a scientific field of study cannot be interpreted in physical terms. The affirmative claim of this article is the fact that human nature can only be understood through the interaction of psychology and neuroscience. Belief in immaterial mental states is not against neuroscience or other life sciences and a definition of human being based on immaterial soul provides an unrivaled coherent ontological basis for defending scientific psychology.