I've heard this argument before, and still don't get it. It borders on the mystical.
Yes, it does. It turns out that carefully developing and applying a physicalist model to subjective experience leads to some very similar conclusions to those of many (especially Eastern) mystics. I can't help that. I didn't set out with any such objective in mind.
If we say our subjective self and pain and all is an "illusion", we are going full tilt Buddhist. Our sense of self is the only "real" thing we can be aware of. All the consequently illusory sensory inputs of data and evidence would fall under the same illusory umbrella, no?
That's why I brought up the term "illusion" in order to object to it. It means too many entirely different things:
- Something we perceive via our senses about the material world that is not actually true of the material world. "The sun circles the earth." "The magician made the lady disappear."
- Something we conclude at one level of cognitive processing of an abstraction, that's not true at a different (more basic) level of cognitive processing of the abstraction: "Square B is lighter than square A."
(Thanks to leumas for the example. Note that if the picture were an accurate photograph of a real collection of objects colored and arranged in a straightforward way, square B would have been colored a lighter shade than square A in those real objects. Our perception would be giving us correct information about the real world, while being inaccurate in its interpretation of the characteristics of the pixels of the photograph. Since the picture is not actually a photograph, it becomes a discrepancy between different levels of interpretation of abstractions instead.)
- Conflating or contrasting our mental categories and other narratives with the physical reality they're modeling. This leads to absurdities if done too little or too much. At one extreme, you get, "you don't really see a tree, you only see your indoctrinated cultural expectations of what a tree is." At the other extreme, you get philosophers arguing for millennia about whether chairs exist or the Ship of Theseus, as if how we describe things is somehow a fundamental intrinsic property of those things. With everyone crying "illusion!" at every step.
Subjective experiences are real. (You're welcome, Descartes.)
The physical world is also real. (Sorry, Descartes.)
But they're real in different ways, subject to different rules.
We can, and should, talk of where subjective experiences more or less accurately correspond to qualities of the physical world, and where they don't. When they don't, we can call it illusion, but there's a big caveat.
If we say "pain is an illusion" we're implying that there's a discrepancy between the subjective experience and the physical world. But if someone experiences pain, what is it that exists in the physical world that's actually not experiencing pain? If there's no such thing, then there's no discrepancy. So there can be convincing near-universal near-unavoidable subjective experiences that don't exist in the physical world, but don't contradict it either. The term "illusion" doesn't apply so well in those cases.
"Free will" is almost but not quite the same. For most of history, if you said free will is an illusion, there's nothing known in the physical world for there to be a discrepancy with. But then the functioning of the brain was discovered, and the question arose whether the brain possesses free will in some physical way (e.g. one of Penrose's theories) or does not, and if it does not, is free will not an illusion? It's an illusion (that is, an erroneous conclusion about the real world) only if we assume that the brain must possess free will in order to have the subjective experience of free will. If instead we accept that free will is a feature of the subjective narrative generated by the brain, then there's nothing else to be the contradicting reality behind the illusion. It only matters whether or not the brain can generate that narrative, not whether or not the brain operates deterministically+possibly randomly when it does so. That's why I think "free will is an illusion" is misleading.
