why should we accept the idea of a non-physical property in this case?
neither the qualitative content (how they feel) or their aboutness (intentionality) of mental states are knowable from a third person point-of-view. so, we have this bizarre predicament that we can know all the physical and functional properties of a mental state (as we've seen with the neuro siences and AI) without knowing "what's like to have it" or "what it is about."
the conclusion that the property is non-physical seems unavoidable.
here is one example, from erwin schrödinger (1887-1961), the famous physicist:
The sensation of color cannot be accounted for by the physicist's objective picture of light-waves. Could the physiologist account for it, if he had fuller knowledge than he has of the processes in the retina and the nervous processes set up by them in the optical nerve bundles and in the brain? I do not think so.not satisfied yet? i understand. these hypothesis are complicated. contrasting them can take the course of a semester (as when you sign for a "philosophy of mind" course). the purpose of this course is to introduce these ideas.