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In his book Consciousness Explained Dennett writes "Anyone or anything that has such a virtual machine as its control system is conscious in the fullest sense" [p281] referring to a Joycean machine which (if I understood correctly) may be implemented/simulated by a Turing machine.

Suppose I define Qualia as that thing which will always be left out by any implementation/simulation of consciousness by a Turing machine.

So it seems Dennett believes that Qualia defined in that sense does not exist.

The surprising thing to me is that most of my friends insist that no such Qualia exists, and they are all intelligent, and often software developers, who I expect, are supposed to know something about the nature of computation, even if only intuitively.

So far I failed to make even one of them realise that there is something in their inner experience that cannot conceivably be reproduced/simulated by a Turing machine.

They are in good company, BTW; here is an amazing "Closer to Truth" interview with Marvin Minsky where he explains away qualia:

Note I am NOT interested in any arguments for or against physicalism, idealism or dualism.

I am curious as to why so often non-philosophers, but nevertheless intelligent people who are supposed to know something about the nature of computation, insist there is nothing in their inner experience which cannot be reproduced/simulated by a Turing machine.

And my request is for references to discussions of this curiosity by philosophers, if such discussions exist.

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I'd be more interested in why you believe that there is. – Roger Aug 25 '14 at 15:52
Because they're wrong. – user4894 Aug 25 '14 at 16:07
Excellent question and very well put. I agree with you and it will be interesting to read the answers here. Perhaps it comes down to whether you believe that qualia are a necessary part of consciousness. – Nick R Aug 25 '14 at 18:06
@user4894 If there exists a set Q defined as "things that a Turing complete implementation cannot simulate", then the onus is on those who believe it to be non-empty to demonstrate that this is the case. The alternative is proving a negative. So my question to the OP is, if the greater number of opinions gathered by people who are, by your own admission, intelligent and competent, disagree with you, should you not try to consider the possibility that it is you, not them, who are wrong? What makes you so certain that you are right, in the absence of any qualitative proof of that? – Roger Aug 25 '14 at 18:56
@Roger A TM is an abstract mathematical construction. A TM can no more be conscious than the set of even integers or the category of topological spaces can. Now perhaps the question means, can an implementation of a TM be conscious; the implication being that humans are implementations of TMs. Which is false, since we are finite. But the claims that we are memory- and time-limited TMs is totally unproven. Our brains don't work like TMs do, with a read/write head making and reading marks on a tape. The more you think about this question the more outlandish it gets. – user4894 Aug 25 '14 at 19:32

In answer to your question, I think Scott Aaronson, a computer scientist at MIT, expresses the strong AI position very eloquently on his blog and in the notes for some of his courses. For instance,

Here's an excerpt in which he mentions qualia:

So, I asked you to read Turing's second famous paper, Computing Machinery and Intelligence. Reactions?

What's the main idea of this paper? As I read it, it's a plea against meat chauvinism. Sure, Turing makes some scientific arguments, some mathematical arguments, some epistemological arguments. But beneath everything else is a moral argument. Namely: if a computer interacted with us in a way that was indistinguishable from a human, then of course we could say the computer wasn't "really" thinking, that it was just a simulation. But on the same grounds, we could also say that other people aren't really thinking, that they merely act as if they're thinking. So what is it that entitles us to go through such intellectual acrobatics in the one case but not the other?

If you'll allow me to editorialize (as if I ever do otherwise...), this moral question, this question of double standards, is really where Searle, Penrose, and every other "strong AI skeptic" comes up empty for me. One can indeed give weighty and compelling arguments against the possibility of thinking machines. The only problem with these arguments is that they're also arguments against the possibility of thinking brains!

So for example: one popular argument is that, if a computer appears to be intelligent, that's merely a reflection of the intelligence of the humans who programmed it. But what if humans' intelligence is just a reflection of the billion-year evolutionary process that gave rise to it? What frustrates me every time I read the AI skeptics is their failure to consider these parallels honestly. The "qualia" and "aboutness" of other people is simply taken for granted. It's only the qualia of machines that's ever in question.

But perhaps a skeptic could retort: I believe other people think because I know I think, and other people look sort of similar to me -- they've also got five fingers, hair in their armpits, etc. But a robot looks different -- it's made of metal, it's got an antenna, it lumbers across the room, etc. So even if the robot acts like it's thinking, who knows? But if I accept this argument, why not go further? Why can't I say, I accept that white people think, but those blacks and Asians, who knows about them? They look too dissimilar from me.

Oh, this is also an entertaining discussion

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Thanks for the references, I'll try to read both the lecture and Turing's paper. However, it seems to me from this excerpt that Aaronson confuses thinking with qualia. I do not think that proponents of qualia, such as Chalmers for example, argue against thinking machines. – nir Aug 27 '14 at 22:23
@nir I think when he says "AI skeptics" he means, in particular, strong AI skeptics, not just skeptics of thinking machines generally, if that clarifies anything. – Tim kinsella Aug 28 '14 at 2:29
I would like to emphasize the notion of meat chauvinism. – Calvin Aug 28 '14 at 20:22
@Timkinsella, the conversation between Yudkowsky and Pigliucci is great! – nir Aug 28 '14 at 21:45

People believe that we have qualia because it seems that e.g. red is like something not reducible to declarative knowledge. (I've never heard a satisfactory account of why procedural knowledge isn't as vexing as qualia. But that's an aside.)

People believe that we are Turing-computable because all the physical processes that seem to be in play in biological systems can be described very well with mathematics that is Turing-computable. Empirically, we can't distinguish our universe from a Turing-computable one (at least at the scale of our consciousness). We can see that those things that we describe well with mathematics have a profound impact on consciousness (e.g. neuron reversal potential).

Because we believe we have qualia because we seem to, and because we believe the universe is Turing computable because we have a staggering quantity of empirical evidence consistent with that hypothesis, and we have no proof (aside from what boils down to argument from increduility, which is notoriously weak--see how well vitalists fared!) that qualia is Turing-incomputible (e.g. qualia cannot solve the halting problem), we conclude that qualia are computable.

Tossing aside computability because of a vague hunch that it feels wrong for qualia is just as foolish as tossing aside qualia because they seem awkward to compute.

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It could be an explanation for why some people believe they are Turing computable, but since most people are not physicist, nor philosophers of mind, and have not bothered very deeply with such questions as whether a galaxy or the universe itself are Turing computable; for such reasons I find it surprising that so many people I talk with (including people answering and commenting here) insist on having nothing in their inner experience which cannot be simulated by a computer; and this is why I am interested in discussions of this phenomena by philosophers. – nir Aug 27 '14 at 20:55
@nir - You can be aware of results from physicists without being a physicist. Why do people believe that stars are far away? They're not astronomers who have calculated parallax or used standard candles or red-shifts etc. – Rex Kerr Aug 27 '14 at 20:58
other notes: a) Chalmers discusses why vitalism is not a good analogy to Qualia in his Facing Up paper. b) (a naive question) why don't we consider the randomness and the absurd aspects of elementary particles the characteristics of an underlying non-computable phenomena? c) doesn't the claim that a Turing machine may be conscious in the fullest sense mean that a string of bits may be conscious in the fullest sense? – nir Aug 27 '14 at 21:17
also, regarding the intuition of people, while some theoretical physicist and philosophers may theorize that the universe is information, or that there is no distinction between a phenomena and its simulation, I would expect ordinary people to distinguish by intuition between a phenomena and its simulation or representation, just as you distinguish between a person and a photograph of that person. – nir Aug 27 '14 at 21:22
@nir - That's pretty hard to answer without knowing what "manifested" actually means, and what the emergent property actually is, if there is one, isn't it? "If you don't have a fully-worked-out answer already, there isn't one" is just an argument from ignorance. When dealing with stupendously complex objects with many amazing and baffling properties, you have to fall back on what general principles you understand. If there is a reason why consciousness is not subject to the sorites paradox, then we can get somewhere. Otherwise it's just hunches flying in the face of empirical evidence. – Rex Kerr Aug 27 '14 at 22:45

As a former professional computer software engineer, physicist, and "thinker" - but perhaps not philosopher - I feel well placed to answer the core of your question:

"...insist there is nothing in their inner experience which cannot be simulated by a Turing machine."

And the answer is simple. These are educated and often pragmatic people who will heuristically and intuitively expect justification for an argument that doesn't match their experience and the progress in science, mathematics, and computation over the last few decades. We have not found any system that cannot at least to a good approximation be simulated using Turing machines, so why should there be any exception? If consciousness etc are emergent properties of complex dynamic systems then if you simulate those complex dynamic systems those same characteristics will emerge based on the evidence of other such simulations - e.g. weather forecasting.

I suppose this is also an intuitive appeal to Occam's Razor's_razor This will be natural to software engineers as it's highly applicable to good software design.

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Regarding intuitions on the nature of simulation and weather forecasting, this reminds me of Searle who said "no one supposes that a computer simulation of a storm will leave us all wet" – nir Aug 28 '14 at 17:12
What is your opinion btw? Will a Turing machine running the perfect simulation of a human brain be conscious in the fullest sense as Dennett put it? – nir Aug 28 '14 at 17:18
I've not read Dennett however my belief is that it is an emergent property so yes I believe if you simulate the underlying systems the rest will follow. And a virtual storm could leave a virtual intelligence wet ;) – Andy Boura Aug 28 '14 at 17:23
It seems that if you accept that it is possible in principle to simulate the brain with a Turing machine, and that such a TM would be conscious in the fullest sense (as we are), you may end up concluding that we are just as conscious as a (giant) piece of paper with a string of symbols written on it (see my exchange of comments with Rex Kerr). Today I talked with two people who admitted that such a piece of paper would be as conscious as they are, and if I correctly understood Rex and Calvin (in the comments to their answers), they believe that too. Can you see a problem there? – nir Aug 28 '14 at 20:47
@nir An interesting exchange above. I didn't follow some of the references in that discussion but I believe I generally agree with Rex. A couple of key points though...the paper is like a "paused brain" is someone brain dead conscious? All their neurons etc are still there. It is the act of execution that causes the emergent consciousness to occur. Also the paper must be capable of storing and amending state if it is not to be permanently locked in an instant. – Andy Boura Aug 28 '14 at 21:20

Any physical system can be simulated by a universal computer. For some purposes the computer in question would have to be a quantum computer. However, the human brain is a wet, warm system in contact with the environment and on the timescale on which though takes place it won't exhibit any distinctively quantum mechanical effects like interference or entanglement. So the human brain can be simulated by a classical computer and the Turing machine can simulate any classical computer. The sense in which the Turing machine can simulate a system not not just that the initial and final states of the computation are the same. The computer can be set up in such a way that there is a mapping between the states of the computer and the way information flows within the system while it is computing the result. For any pattern of information flow in the brain while it is instantiating consciousness, that pattern could be instantiated in some function of the Turing machine's tape. For reasons that I think Dennett explains it might not be a good idea to simulate the brain in that way. The brain's architecture looks nothing like a Turing machine and there is no particular reason to translate what it is doing so that it can be run by the Turing machine if some other architecture would work faster and use less memory, e.g. - a network of computational gates.

You say

So far I failed to make even one of them realise that there is something in their inner experience that cannot conceivably be simulated by a Turing machine.

I'm not entirely clear on why anyone would say that something that has not been explained (consciousness) cannot be simulated by a computer. I am not aware of any clear statement of what problem is solved by postulating qualia in the sense you gave above. If you haven't explained consciousness and don't have a clear statement of the problem, then you can't have an argument for saying that consciousness can't be simulated. You might want to read "Godel, Escher, Bach: an Eternal Golden Braid" by Douglas Hofstadter if you haven't already.

It is true that no explanation of how consciousness is instantiated in the brain has been given. It is also true that no explanation of what sort of program could simulate consciousness has been given. I think it is also true that both Dennett and his critics have some bad philosophical misconceptions that may obstruct their efforts. For an article that describes some of the problems, see

Dennett and other people working on this areas also have problematic moral ideas that might pose a problem, see "The Meaning of Mind: Language, Morality and Neuroscience" by Thomas Szasz.

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a) there is evidence of quantum effects in (warm and wet) plants, and this possibly means that what you say about the brain is wrong. – nir Sep 1 '14 at 18:30
b) while it is indeed my position, I did not write that consciousness cannot be simulated; what I wrote is that I find it very surprising that most people I talk with, do not find anything in their inner experience which may not be simulated by a Turing machine; Calvin, Rex and Andy write in the comments to their answers here that a string of symbols may be conscious in the fullest sense. I am surprised that not only this position is so common, but that people refuse to see any difficulty in it. – nir Sep 1 '14 at 19:00
About (a), that describes events in single molecules, not spread over a region of many cubic centimetres taking place over something like 0.1 seconds. A single molecule can't be wet since that is a description of a bulk property of many molecules. I'm not convinced you can assign a single molecule a temperature either although if you have an explanation of thermal equilibration that implies that a single molecule can have a temperature that would be interesting. – alanf Sep 2 '14 at 8:51
Since a Turing machine can (albeit often inefficiently) simulate anything that can be simulated, your position implies that consciousness can't be simulated. Also, what's happening in your brain is basically that there are loads of chemical and electrical switches whose state could be interpreted as similar to the symbols that can be written on a paper tape. Those symbols are being changed according to the relevant laws of physics, all of which instantiate the same set of computable functions as the Turing machine, – alanf Sep 2 '14 at 9:01

I am curious as to why so often non-philosophers, but nevertheless intelligent people who are supposed to know something about the nature of computation, insist there is nothing in their inner experience which cannot be simulated by a Turing machine.

I'm no expert at all and do believe in qualia anyway, but suggest it's because of fear of difficult problems. life is easier to model if life doesn't have qualia. in a similar way that psychologists often act with physics envy and are dazzled by models that are highly mathematical and so do away with more troubling facets of psychology.

And so greedy reductionism (though of course, Dennett wouldn't use the term here)

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As philosophers, we strive to explain complex ideas with rational argument. The mind computes; TMs explain compution. There is no fear, only synthesis. – Calvin Aug 25 '14 at 19:59
shoddy synthesis [which you admit is possible] is a sign of if not fear motivation then still an over quickness IMO – MATHEMETICIAN Aug 25 '14 at 20:03
@user3293056, thanks for the reference; I can see how greedy reductionism may explain positions taken by philosophers; however, with "laypersons" like me and people I talk with, it seems more as if they really don't see the problem. – nir Aug 25 '14 at 20:11
Naturally imperfect synthesis is possible. But I don't think a completely undefined Qualia is evidence to overturn the Turing Hypothesis. – Calvin Aug 25 '14 at 22:13
@user3293056 I'm not really trying to be confrontational here, but consider this. Science seeks to explain natural events with natural causes. The Turing hypothesis does this. Beyond the bounds of science, there is no objective argument for anything really, just philosophical ones. To take nothing away from philosophical arguments, they fundamentally rely on unprovable premises (thanks Godel! - who also produced a TM equivalent by the way) that are necessarily taken on faith. Believing in Qualia or not believing in it are basically religions. – Calvin Aug 27 '14 at 14:49

Well, as a computer scientist, to me, your mind is a series of one bit processors (neurons) wired together on a direct weight graph (nerves). I understand that this model is based on physicalism, but it may also be completely formulated mathematically and I find it to predict my actions accurately. I would argue that there is considerable evidence that our understanding of mathematics is philosophically credible.

I'm entirely uncertain what about that I can't simulate on a Turing Machine, or what esle, if this is incomplete explanation, couldn't be simulated.

In that sense, I believe the onus is on you to provide any reason at all whatsoever that there would be any part of consciousness that isn't Turing complete. I'd say that this requires an explicit definition of consciousness.

That is, I'm struggling to see any reasonable question here without a hard definition on Qualia. Because any Qualia that I can think of, as my mind is Turing complete, would necessarily also be Turing complete.

I hope that makes sense.

Thank you.


Edit: I thought I should produce a Turing machine.

Let us take as given that you have a finite lifespan.

Let us also take as given you can think a finite number of thoughts at any given point in time.

Let us also take as given that thoughts take non-zero time, so that time may be discretized.

Suppose then that Goddess monitors your every thought and constructs a Turing machine that procedurally outputs your exact thoughts under your same circumstances. Note that this machine would have a finite number of states.

I'd consider that an existence proof of you as Turing complete.

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Life was not listed as a pre-requisite for consciousness. – Calvin Aug 25 '14 at 18:32
that's interesting! but then again, why care about consciousness then? – MATHEMETICIAN Aug 25 '14 at 18:36
"your mind is a series of one bit processors (neurons) wired together on a direct weight graph" -- This is totally not how neurons and brains work. You should read up on the subject. – user4894 Aug 25 '14 at 19:34
The mind trivially isn't a TM. It does, however, reduce. Everything computable in nature is computable on a TM by Turing Hypothesis. I feel fairly confident resting my lemma on that hypothesis given its strength. One bit processors on a directed graph is a very near approximation of the mind, likewise its inputs and outputs all function on integers. Any remaining complications are biological rather than philosophical discussion, and certainly bring nothing to bare against the Turing Hypothesis. – Calvin Aug 25 '14 at 19:56
@nir If you can encode a galaxy in a string, you can encode me in a string. I certainly seem to fully conscious up to a reasonable degree of certainty. Then, to me, it makes no difference what method I'm encoded in. Perhaps we're all just simulated TMs running on a universal TM anyway and I am just a string. That would model our existence just as well as any other unification theory. – Calvin Aug 27 '14 at 14:57

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