[Cross-posted.]
1. Defining the problem: The inverted spectrum
Philosophy has been called a preoccupation with the questions entertained by adolescents, and one adolescent favorite concerns our knowledge of other persons’ “private experience” (raw experience or qualia). A philosophers’ version is the “inverted spectrum”: how do I know you see “red” rather than “blue” when you see this red print? How could we tell when we each link the same terms to the same outward descriptions? We each will say “red” when we see the print, even if you really see “blue.”
The intuition that allows us to be different this way is the intuition of raw experience (or of qualia). Philosophers of mind have devoted considerable attention to reconciling the intuition that raw experience exists with the intuition that inverted-spectrum indeterminacy has unacceptable dualist implications making the mental realm publicly unobservable, but it’s time for nihilism about qualia, whose claim to exist rests solely on the strength of a prejudice.
A. Attempted solutions to the inverted spectrum.
One account would have us examine which parts of the brain are activated by each perception, but then we rely on an unverifiable correlation between brain structures and “private experience.” With only a single example of private experience—our own—we have no basis for knowing what makes private experience the same or different between persons.
A subtler response to the inverted spectrum is that red and blue as experiences are distinct because red looks “red” due to its being constituted by certain responses, such as affect. Red makes you alert and tense; blue, tranquil or maybe sad. What we call the experience of red, on this account, just is the sense of alertness, and other manifestations. The hope is that identical observable responses to appropriate wavelengths might explain qualitative redness. Then, we could discover we experience blue when others experience red by finding that we idiosyncratically become tranquil instead of alert when exposed to the long wavelengths constituting physical red. This complication doesn’t remove the radical uncertainty about experiential descriptions. Emotion only seems more capable than cognition of explaining raw experience because emotional events are memorable. The affect theory doesn't answer how an emotional reaction can constitute a raw subjective experience.
B. The “substitution bias” of solving the “easy problem of consciousness” instead of the “hard problem.”
As in those examples, attempts at analyzing raw experience commonly appeal to the substitution process that psychologist Daniel Kahneman discovered in many cognitive fallacies. Substitution is the unthoughtful replacement of an easy for a related hard question. In the philosophy of mind, the distinct questions are actually termed the “easy problem of consciousness” and the “hard problem of consciousness,” and errors regarding consciousness typically are due to substituting the “easy problem” for the “hard,” where the easy problem is to explain some function that typically accompanies “awareness.” The philosopher might substitute knowledge of one’s own brain processes for raw experience; or, as in the previous example, experience’s neural accompaniments or its affective accompaniments. Avoiding the “substitution bias” is particularly hard when dealing with raw awareness, an unarticulated intuition; articulating it is a present purpose.
2. The false intuition of direct awareness
A. Our sense that the existence of raw experience is self-evident doesn’t show that it is true.
The theory that direct awareness reveals raw experience has long been almost sacrosanct in philosophy. According to the British Empiricists, direct experience consists of sense data and forms the indubitable basis of all synthetic knowledge. For Continental Rationalist Descartes, too, my direct experience—“I think”—indubitably proves my existence.
We do have a strong intuition that we have raw experience, the substance of direct awareness, but we have other strong intuitions, some turn out true and others false. We have an intuition that space is necessarily flat, an intuition proven false only with non-Euclidean geometries in the 19th century. We have an intuition that every event has a cause, which determinists believe but indeterminists deny. Sequestered intuitions aren’t knowledge.
B. Experience can’t reveal the error in the intuition that raw experience exists.
To correct wayward intuitions, we ordinarily test them against each other. A simple perceptual illusion illustrates: the popular Muller-Lyer illusion, where arrowheads on a line make it appear shorter than an identical line with the arrowheads reversed. Invoking the more credible intuition that measuring the lines finds their real length convinces us of the intuitive error that the lines are unequal. In contrast, we have no means to check the truth of the belief in raw experience; it simply seems self-evident, but it might seem equally self-evident if it were false.
C. We can’t capture the ineffable core of raw experience with language because there’s really nothing there.
One task in philosophy is articulating the intuitions implicit in our thinking, and sometimes rejecting the intuition should result from concluding it employs concepts illogically. What shows the intuition of raw experience is incoherent (self-contradictory or vacuous) is that the terms we use to describe raw experience are limited to the terms for its referents; we have no terms to describe the experience as such, but rather, we describe qualia by applying terms denoting the ordinary cause of the supposed raw experience. The simplest explanation for the absence of a vocabulary to describe the qualitative properties of raw experience is that they don’t exist: a process without properties is conceptually vacuous.
D. We believe raw experience exists without detecting it.
One error in thinking about the existence of raw experience comes from confusing perception with belief, which is conceptually distinct. When people universally report that qualia “seem” to exist, they are only reporting their beliefs—despite their sense of certainty. Where “perception” is defined as a nervous system’s extraction of a sensory-array’s features, people can’t report their perceptions except through beliefs the perceptions sometimes engender: I can’t tell you my perceptions except by relating my beliefs about them. This conceptual truth is illustrated by the phenomenon of blindsight, a condition in patients report complete blindness yet, by discriminating external objects, demonstrate that they can perceive them. Blindsighted patients can report only according to their beliefs, and they perceive more than they believe and report that they perceive. Qualia nihilism analyzes the intuition of raw experience as perceiving less than you believe and report you perceive, the reverse of blindsight.
3. The conceptual economy of qualia nihilism pays off in philosophical progress
Eliminating raw experience from ontology produces conceptual economy. A summary of its conceptual advantages:
A. Qualia nihilism resolves an intractable problem for materialism: physical concepts are dispositional, whereas raw experiences concern properties that seem, instead, to pertain to noncausal essences. If raw experience was coherent, we could hope for a scientific insight, although no one has been able to define the general character of such an explanation. Removing a fundamental scientific mystery is a conceptual gain.
B. Qualia nihilism resolves the private-language problem. There seems to be no possible language that uses nonpublic concepts. Eliminating raw experience allows explaining the absence of a private language by the nonexistence of any private referents.
C. Qualia nihilism offers a compelling diagnosis of where important skeptical arguments regarding the possibility of knowledge go wrong. The arguments—George Berkeley’s are their prototype—reason that sense data, being indubitable intuitions of direct experience, are the source of our knowledge, which must, in consequence, be about raw experience rather than the “external world.” If you accept the existence of raw experience, the argument is notoriously difficult to undermine logically because concepts of “raw experience” truly can’t be analogized to any concepts applying to the external world. Eliminating raw experience provides an effective demolition; rather than the other way around, our belief in raw experience depends on our knowledge of the external world, which is the source of the concepts we apply to fabricate qualia.
4. Relying on the brute force of an intuition is rationally specious.
Against these considerations, the only argument for retaining raw experience in our ontology is the sheer strength of everyone’s belief in its existence. How much weight should we attach to a strong belief whose validity we can't check? None. Beliefs ordinarily earn a presumption of truth from the absence of empirical challenge, but when empirical challenge is impossible in principle, the belief deserves no confidence.
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If Q genuinely has infinite cardinality, then its members cannot all be equal to one another. If you take, at random, any two purportedly distinct members of Q u and w, then it has to be the case that u is not equal to w. If the members were all equal to each other, then Q would have cardinality 1. So the members of Q have to be distinguishable in at least this sense -- there needs to be enough distinguishability so that the set genuinely has cardinality infinity. If you can actually build an infinite set of quarks or Platonic points, it cannot be the case that any arbitrary quark (or point) is identical to any other. If one accepts the principle of identity of indistinguishable, then it follows that quarks or points must be distinguishable (since they can be non-identical). But you need not accept this principle; you just need to agree with me that the members of the set Q cannot all be identical to one another.
Now, the criterion for identity of two sets A and B is that any z is a member of A if and only if it is a member of B. In other words, take any member of A, say z. If A = B you have to be able to find some member of B that is identical to z. But this is not true of the sets Q and Q\Bob. There is at least one member of Q which is not identical to any member of Q\Bob -- the member that was removed when constructing Q\Bob (which, remember, is not identical to any other member of Q). So Q is not identical to Q\Bob. There is no separate criterion for the identity of sets which leads to the conclusion that Q is identical to Q\Bob, so we do not have a contradiction.
Believe me, if there was an obvious contradiction in Zermelo-Fraenkel set theory (which includes an axiom of infinity), mathematicians would have noticed it by now.
I accept the principle, but I think it isn't relevant to this part of the problem. I can best elaborate by first dealing with another point.
True, but my claim is that there is a separate criterion for identity for actually realized sets. It arises exactly from the principle of the identity of indistinguishables. Q and Q/Bob are indistinguishable when the elements are indistinguishable; they should be distinguishable despite the elements being indistinguishable.
What justifies "suspending" the identity of indistinguishables when you talk about elements is that it's legitimate to talk about a set of things you consider metaphysically impossible. It's legitimate to talk about a set of Platonic points, none distinguishable from another except in being different from one another. We can easily conceive (but not picture) a set of 10 Platonic points, where selecting Bob doesn't differ from selecting Sam, but taking Bob and Sam differs from taking just Bob or just Sam. So, the identity of indistinguishables shouldn't apply to the elements of a set, where we must represent various metaphysical views. But if you accept the identity of indistinguishables, an infinite set containing Bob where Bob isn't distinguishable from Sam or Bill is identical to an infinite set without Bob.
I'll take your word on that, but I don't think it's relevant here. I think this is an argument in metaphysics rather than in mathematics. It deals in the implications of "actual realization." (Metaphysical issues, I think, are about coherence, just not mathematical coherence; the contradictions are conceptual rather than mathematical.) I don't think "actual realization" is a mathematical concept; otherwise--to return full circle--mathematics could decide whether Tegmark's right.
Among metaphysicians, infinity has gotten a free ride, the reason seeming to be that once you accept there's a consistent mathematical concept of infinity, the question of whether there are any actually realized infinities seems empirical.