against the knowledge argument
Consider a color scientist named Mary who has never seen red. She lived in a black and white environment with special contact lenses all her life, so she'd never seen most colors. Then she went on to learn the neuroscience of color perception. She now knows everything there is to know from science about color perception. She knows what color words apply to which wavelengths of light. She knows what goes on in the brain when people see various colors. But she's never seen red. Then she takes off the contact lenses, and someone gives her a tomato. She now sees red for the first time. Does she learn something?
- Mary knows every physical fact about color perception.
- There's a fact about color perception that Mary learns when she sees red - namely, what it is like to experience seeing that color.
- Therefore, there are more than just physical facts (so materialism is false).
Because everyone has these limitations it is hard to imagine mary not having these limitations. But the existance of such limits dont threaten physicalism.
Or more simply we seem very far from being able to imagine "all the physical facts about colour perception". Because we are so far from doing this it seems unclear why we should expect our intuition (sense of implausibility) to be accurate regarding what isn't part of that set.