What Mises says in Human Action is that in our current state of knowledge we must accept methodological dualism. The deterministic cause-and-effect in the material world and the scientific method of discovering the quantitative magnitudes of cause and effect relationships in the material world have not been successfully applied to the realm of human action. There is no theory describing the quantitatively precise relationship between material factors in the world and ideas in the mind that has been established, or not falsified at least, by the scientific method. We must, therefore, conceive of the cause and effect relationships between ideas in the mind and things in the world in a different way and discover cause and effect relationships between the mind and the material world with a method other than the scientific method. Mises calls this method, praxeology.