"P-zombie" is not a coherent leftover possibility once you fix the full physical structure. If a system has the full self-model (temporal-spatial sense) / world-model / memory binding / counterfactual evaluator / control loop, then that structure is what having experience amounts to (no extra ingredient need be added or subtracted).
I hope I don't later get accused of plagiarizing myself, but let's embark on a thought experiment. Imagine a bitter, toxic alkaloid that does not taste bitter. Suppose ingestion produces no distinctive local sensation at all – no taste, no burn, no nausea. The only "response" is some silent parameter in the nervous system adjusting itself, without crossing the threshold of conscious salience. There are such cases: Damaged nociception, anosmia, people congenitally insensitive to pain. In every such case, genetic fitness is slashed. The organism does not reliably avoid harm.
Now imagine a different design. You are a posthuman entity whose organic surface has been gradually replaced. Instead of a tongue, you carry an in‑line sensor which performs a spectral analysis of whatever you take in. When something toxic is detected, a red symbol flashes in your field of vision: “TOXIC -- DO NOT INGEST.” That visual event is a quale. It has a minimally structured phenomenal character -- colored, localized, bound to alarm -- and it stands in for what once was bitterness.
We can push this further. Instead of a visual alert, perhaps your motor system simply locks your arm; perhaps your global workspace is flooded with a gray, oppressive feeling; perhaps a sharp auditory tone sounds in your private inner ear. Each variant is still a mode of felt response to sensory information. Here's what I'm getting at with this: There is no way for a conscious creature to register and use risky input without some structure of "what it is like" coming along for the ride.
1. Qualia exist as something separate from functional structure (so p-zombies are conceivable)
2. Qualia don't exist at all (Dennett-style eliminativism)
But I say that there is a third position: Qualia exist, but they are the internal presentation of a sufficiently complex self-model/world-model structure. They're not an additional ingredient that could be present or absent while the functional organization stays fixed.
To return to the posthuman thought experiment, I'm not saying the posthuman has no qualia, I'm saying the red "TOXIC" warning is qualia. It has phenomenal character. The point is that any system that satisfies certain criteria and registers information must do so as some phenomenal presentation or other. The structure doesn't generate qualia as a separate byproduct; the structure operating is the experience.
A p-zombie is only conceivable if qualia are ontologically detachable, but they're not. You can't have a physicalism which stands on its own two feet and have p-zombies at the same time.
Also, it's a fundamentally silly and childish notion. "What if everything behaves exactly as if conscious -- and is functionally analogous to a conscious agent -- but secretly isn't?" is hardly different from "couldn't something be H2O without being water?," "what if the universe was created last Thursday with false memories?," or "what if only I'm real?" These are dead-end questions. Like 14-year-old-stoner philosophy: "what if your red is ackshuallly my blue?!" The so-called "hard problem" either evaporates in the light of a rigorous structural physicalism, or it's just another silly dead-end.
> "couldn't something be H2O without being water?," "what if the universe was created last Thursday with false memories?," or "what if only I'm real?" These are dead-end questions. Like 14-year-old-stoner philosophy: "what if your red is ackshuallly my blue?!"
These are all legitimate philosophical problems, Kripke definitively solved the first one in the 1970s in Naming and Necessity. You should try to be more humble about subjects which you clearly haven't read enough about. Read the Mary's room argument.