The phrase "Even though Mary knows all the physical facts" is precisely the fallacy of begging the question that Prof. Churchland is alluding to. When Mary leaves the room, regardless of whether she has "normal" color vision or not, a new part of her brain gets stimulated, enabling her to create new representations and memories of color in terms of brain states. Since representations and memories are grounded in physical properties, it follows that Mary did not, in fact, know all the physical facts about color. The knowledge argument implicitly assumes that whatever Mary learns cannot be represented in terms of physical properties, meaning that its conclusion is contained within its premise. Hence the fallacy of begging the question.

@@shreyas5886 I understand whaat you are saying, and if all Jackson was claiming was that "Mary knows all the physical facts", without giving a reason to support that, it would be question-begging. That's why I wrote those two final sentences. The underlying premise is that any physical fact must be knowable regardless of whether it has been consciouly experienced. What it is like to experience red is not such a fact.

@@Brian.001 I understand your argument as well. But my point is that the claim that "any physical fact must be knowable regardless of whether it has been consciously experienced" implicitly assumes a dualism between conscious experience and physical facts. If one already accepts such a dualism, then physicalism cannot be true. The question for physicalism is, how can physical facts explain conscious experience? No one has offered a satisfactory answer to that question yet. But I believe it is doable, and I am currently working on a paper on the subject. But regardless of whether physicalism is true or not, I believe the knowledge argument is flawed, because the formulation of the argument itself assumes certain limits on physicalist theories that are widely believed to be true, but are not entailed by the ontology of physicalism. Indeed, the belief that all physical facts are knowable regardless of experience is so commonplace even among physicalists, that it leads illusionists like Dan Dennett to give rather dubious responses to the knowledge argument.

@@shreyas5886 "... implicitly assumes a dualism between conscious experience and physical facts." Again, there is an implicit premise to that effect, but I wouldn't say it is unsupported. We have to ask ourselves what we even mean by 'the physical'. If we just accept that it means 'occuring within the dimensions of time and space', it is but a short hop to the next inference; that physical states and events are those that can be observed and described in 3rd-person terms. Anyone who makes the right observations can obtain the same results. This doesn't apply to my experience of redness, though. Only the person having it can ascertain its quality. If we adopt this conceptual framework, it is clear that the character of conscious experiences falls outside our concept of 'the physical'. You might not be compelled to accept this, but what I am claiming is that the fundamental starting point for the argument is more a conceptual than an empirical one, and as such does not beg the question at the level you suggest.

@@Brian.001 thanks for a really well articulated response. While I accept the premise that "Anyone who makes the right observations can obtain the same results", my claim is that in the context of consciousness, the "right observations" are impossible to make. According to my physicalist viewpoint, consciousness occurs due to a feedback between distinct information processing modules that are emergent from neural activity at a coarser grain. So the way I would describe your experience of redness consists of two processes: 1) There is one information processing module that integrates information from sensory inputs as well as memory. 2) There is a second information processing module that analyzes the integrated information produced by the first one. My claim is that you experience redness when both modules are present and interact within your brain. Now even if I can measure your neural activity with infinite resolution and precision, and I know exactly how to coarse-grain over that activity to describe the two modules, it would be impossible for me to recreate your experience of redness, because any information about your neural activity patterns have to enter through a completely different path into my brain, and therefore form a completely different representation when viewed by my brain's information processing modules. Even if I were somehow able to surgically modify my brain to have the same emergent modules that you have in yours, my memory would be integrated with my sensory inputs in a different way than yours, and we are continually subjected to distinct stimuli from within our own bodies, which would also interfere with our conscious experiences. In short, the interpretation of integrated information within your brain as performed by your brain versus by any external system would necessarily be different, which is what leads to the privatization of yours, and indeed everyone's experiences. And all of this follows from purely physical processes. Hence my rejection of the popular assumption about physicalism that you have nicely laid out. But anyway, these discussions are very fascinating and can go on indefinitely, so best to call it a day here. I believe that we are on the same page about what the argument implies, even if our view differ somewhat on what physicalism is and entails. Thank you very much for your time and for a very illuminating exchange.