Philosophical zombies by definition (See Chalmers: https://consc.net/zombies-on-the-web/) lack qualia, while being normal human beings in every other way. Like normal humans, zombies make utterances that appear to claim that they (zombies) have qualia.

If the inverted spectrum thought experiment makes sense for normal humans, does it still make sense when one replaces the normal humans with zombies? I don't mean inverted qualia, because, as Conifold has pointed out in a comment, a zombie has no qualia by definition, and therefore the answer would be of course, trivially, "no". But, according to Keith Frankish (https://twitter.com/keithfrankish/status/1659626995972489238?s=20 and https://twitter.com/keithfrankish/status/1659945605781700608?s=20 ) they might be visually inverted in other, functional ways, with one possibility being an inversion of affective responses to colors (see Dennett's fictional Mr. Clapgras in "Sweet Dreams" (here's a free pdf of the book, seemingly legal and free and safe, having been uploaded by Dennett himself: https://www.researchgate.net/profile/Daniel-Dennett/publication/329650273_Sweet_Dreams_Philosophical_Obstacles_to_a_Science_of_Consciousness/links/5d7a62ad299bf1ec8bd3573b/Sweet-Dreams-Philosophical-Obstacles-to-a-Science-of-Consciousness.pdf). Of course, such an inversion of emotional responses to colors would be experimentally detectable.

It is usual in discussions of zombies to ignore the possibility that normal humans lack qualia, since so few philosophers acknowledge that this is a real possibility with an appreciable chance of being the case. I am following this convention in this question but feel free to claim (as Dan Dennett does, for example in his book "Consciousness Explained" a free "precis", which is, in my humble opinion, actually more of a brief description of the book than a true precis of it, but is nevertheless worth reading, of which by Dennett can be read for free (at https://www.researchgate.net/publication/270356775_Consciousness_Explained/link/5f3d392d92851cd30203cdc1/download) and as Keith Frankish does in this video: "Lecture 1: The Illusionist Option" https://www.youtube.com/watch?v=Y2n-s6C1iYQ&list=PLhgvALi0LQGXIA7cKNmGNTiQ7dpS-7dLw) that we do lack qualia in your answer.

  • 1
    If the question is whether the inverted spectrum makes sense for zombies then the answer is trivially no. The inversion applies to qualia, which zombies lack. Is there any other question here?
    – Conifold
    Commented May 19, 2023 at 16:47
  • @Conifold Good points. Question edited just now. Commented May 20, 2023 at 16:41
  • Cogito a good understanding of basic logic should light yer way, but do note logic's not foolproof. Sad, nevertheless true.
    – Hudjefa
    Commented May 21, 2023 at 1:47
  • @AgentSmith How is logic not foolproof? Commented May 21, 2023 at 2:06
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    @MatthewChristopherBartsh Classical logic suffers from contradictions in some applications to infinitesimals and infinities, as the Greeks noted. Also none of our knowledge satisfies LEM due to uncertainty. More recently Gödel showed indeterminacy is irresolvable. And language as an only approximate translator of meaning applies to both natural and logic languages (section 9 of Two Dogmas). Science and reasoning use four state logic, all of which violate LEM. The efforts to find a completely applicable and valid logic have led to the realization of an infinity of different logics.
    – Dcleve
    Commented May 21, 2023 at 14:31

3 Answers 3


The p-zombie thought experiment explores the empiricist claim that consciousness is nothing more than its empirical footprint. To appear conscious is to be conscious. This idea was explored by the original "Turing test" thought experiment.

The inverted spectrum thought experiment explores the claim that there can be meaningful internal experiences with no external empirical footprint. The idea is that one cannot tell from the outside whether a person is experiencing an inverted spectrum.

Since the p-zombie has no internal experiences, and the inverted spectrum is purely internal, the p-zombie cannot have an inverted spectrum by definition. The two experiments are designed in such a way that there can be no overlap.


In the article to which you turn for a definition of philosophical zombies (https://consc.net/zombies-on-the-web/), Chalmers writes "their defining features is that they lack conscious experience, but are behaviorally (and often physically) identical to normal humans... The sort I'm most concerned with are zombies that are physically and behaviorally identical to a conscious human, but lack any conscious experience." [my emphasis.]

As Frankish says, however, your zombies would be experimentally detectable. By so being, they would not be the sort of zombie Chalmers needs for his (in)famous argument against physicalism, which claims to establish the metaphysical possibility of mental or psychological differences between individuals in the absence of any physical difference.

One is free to assert the conceivability of these zombies independently of any consideration of whether zombies of the sort you are proposing are either conceivable, metaphysically possible or possible in the actual world, so it seems unlikely that the latter can be used in either supporting or refuting Chalmers' argument.


Your question misapprehends qualia. Qualia are not the units of sensory data but the units of consciousness. It is not just colors which are quales, but also emotions, and the ideas and intuitions by which we reason. A zombie, lacking consciousness, will not have an emotional response. So no, a zombie cannot have an inverted emotional response to colors either.

Further critique, we conscious humans have different emotional responses to colors. You are presuming that all humans will have the same emotional responses to the same color quale, and different responses imply that conscious humans have perhaps scrambled spectra relative to each other. This is an unsupported assumption, and is implausible given our knowledge of psychology (experiences dramatically change one’s emotional response to stimuli), and evolutionary variance.

For a critique of Blackmore’s (and therefore of Dennett’s delusionism see my review here: https://www.amazon.com/Consciousness-Short-Introduction-Susan-Blackmore/dp/0192805851

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