This is about a "thought experiment" called Mary's Room. It's discussed in this Wikipedia article. Here is a short description: Mary is a brilliant scientist who has studied color. She supposedly knows everything there is to know about color. But she has never seen the color red because she has spent her whole life in a black and white room. Nothing in this room has ever had any color. One day Mary leaves her room and actually does see red. The question is, does she learn anything new?
Of course she does. There's nothing mind-blowing about that. Every boy or girl in a sex-ed class highly suspects descriptions of sex are not the same as the real thing.
But philosophers got carried away with their conclusions about this experiment. It was designed by Frank Jackson to show there is more to reality than the physical. If Mary knows all the physical properties of light, including red, and knows how the human eye detects red, she still knows nothing about experiencing red. Therefore the brain must have some aspect that depends on a non-physical 'substance' that allows for this experience. Philosophers call this 'qualia.'
I'll ignore the fact that Mary herself would know she has never experienced red. I don't even need to argue this to demonstrate the experiment cannot detect there is a non-physical aspect to reality.
Suppose we were going to test if a match requires oxygen to light. We construct an experiment similar to Mary's Room. Inside the room we remove all oxygen gas. We strike a match. It doesn't light. We go outside into the oxygen rich atmosphere and strike a match. It lights. It's reasonable to conclude oxygen is required to light the match. We have tested two cases where (probably) only one relevant variable has changed -- oxygen content.
But in Jackson's thought experiment no such control over the (non-physical) variable in question is exercised. I'll assume the dualist position is correct. The only way to test for this non-physical 'substance' is to create an environment in which the substance does not exist. In this case Mary would have to be drained of her extra non-physical substance while inside her room. She is not drained of that substance. We know this because she still experiences black and white which is exactly what that mysterious qualia depends on. When she exits the room the extra, non-physical substance is exactly the same. Only the physical environment has changed. So the variable we want to test (a non-physical substance, or 'oxygen') is not a variable in this test. Jackson has created a bogus test. He does not test for the substance in question. He merely begs the question.
The fact that so-called philosophers think Mary's Room is evidence for dualism simply shows the poor state of modern philosophy. They seem to have lost the ability to think clearly.
-- Don Jindra
