Simple: Find something that the brain does that could not, in principle, be emulated by a Turing machine or equivalent. So far we don't know of any such thing (since quantum mechanics is computable and everything including the brain is ultimately quantum mechanics).
Restricting brain activity to computation it becomes more difficult to find exceptions to the argument. I think this is because computation is fundamentally quite alien to human minds, insofar as it is not an elementary, inescapable mental state. Many philosophers of mind (though not all, particularly not those who adhere to reductive physicalism and eliminative materialism) would characterise phenomenal consciousness and intentionality as these unavoidable mental properties.
It is worth mentioning that there are at least good reasons to reject nearly all of these theories (including physicalist and material thesis). Many aspects of each theories turn out to imply highly unintuitive effects. But I would recommend you read for yourself, since the mind-body problem is immense and very interesting at every step. The SEP articles on both of these[1][2] are quite good.
Elsewhere in this thread some have pointed out that the ontological assumptions of philosophers fade away as we approach the mind in our inquiry. This is at least partly because the mind stretches our understanding of knowledge and matter themselves, and to an even greater degree, our intuitions thereof.
True random number generation can't be done by a deterministic computer, and it appears that human brains can, although not conclusive yet, and the precise mechanism is unclear:
I thought humans were pretty widely considered to be terrible random number generators. We tend to produce sequences that are too uniform, not streaky enough, and contain patterns.
The first related article linked from your link was "Humans cannot consciously generate random numbers sequences: Polemic study." (https://www.ncbi.nlm.nih.gov/pubmed/17888582)
Turing machines, without qualifiers, usually means deterministic ones. Extending it for probabilistic is quite ok, but non deterministic ones are a completely different beast.
"True random number" is a set of statistical tests, which means they can be deterministically fooled. Humans have a lot more inputs than your typical computer, so it's not surprising that their outputs can seem random.
It's worth noting that the theory that a falsifiable hypothesis constitutes scientific investigation (as proposed by Popper) isn't really the gold standard of the philosophy of science any more - especially since Popper's formulation is known to be pretty shoddy.
Not at all, just that the pure theory of falsificationism as specified by Popper both excludes valid science, and includes pseudoscience (for instance, astrology is falsifiable). Thus, falsifiablity is not both necessary and sufficient[0].
The core tenet of science is testing of hypotheses. Any hypothesis that's not falsifiable is by definition not scientifically testable.
Astrology itself is not scientific but, if you use a version of it that's falsifiable, you absolutely can do a valid scientific study on it by making astrological predictions and then testing to see whether they come true. I think it's pretty widely agreed that we've already done this and the (valid scientific) result was negative.
>Any hypothesis that's not falsifiable is by definition not scientifically testable.
This is beside the point. The point of contention is whether or not falsifiability is what makes science what it is, or should be. Genuine science (such as exploratory papers) very often does not start by specifying a falsifiable hypothesis. Bad science, such as astrology, does often propose falsifiable hypotheses. Therefore, astrology can be falsifiable. Therefore, according to Popperian demarcation, astrology counts as science, or it's scientific (useful to remember that Popper counted Darwinian evolution as non-science).
Falsifiability isn't enough for something to be science; it's not necessary and sufficient - because otherwise astrology is science, and exploratory research, popular in many scientific fields, isn't science. The fact that astrology's claims have been falsified does not discount it as science, since a great number of genuine scientific papers also successfully falsify their hypotheses - finding a null result is an example of falsifying a hypothesis.
> Genuine science (such as exploratory papers) very often does not start by specifying a falsifiable hypothesis.
There is plenty of useful work which doesn't specify a falsifiable hypothesis, but it's not science until it does so.
> Therefore, astrology can be falsifiable. Therefore, according to Popperian demarcation, astrology counts as science, or it's scientific
No. Again, being falsifiable means that astrology can be a subject of scientific study. It doesn't make it science in and of itself.
Science is work that follows the scientific process: Choose a question to answer, formulate a hypothesis, make testable predictions based on the hypothesis, test the predictions, analyze and report the results. We can come with a new term (maybe 'pondering'?) for trying to answer questions without testing hypotheses, but by definition it won't be science.
>There is plenty of useful work which doesn't specify a falsifiable hypothesis, but it's not science until it does so.
That's quite a bold statement which is not supported by current work in the philosophy of science. Would you be willing to claim that most papers submitted to Nature don't count as science?
>No. Again, being falsifiable means that astrology can be a subject of scientific study. It doesn't make it science in and of itself.
The claim was that falsifiability is necessary and sufficient to count as science - so really we're in agreement. Making falsifiable claims is not necessary and sufficient demarcation of science and pseudo-science. You need something more than falsifiability to distinguish science from pseudo-science. The question is: what is that thing?
>but by definition it won't be science.
By whose definition? You're sending mixed messages - why is physics a science, rather than merely capable of being a subject of scientific study? We can make claims in physics that are just as falsifiable as the ones in astrology.
It's also unwise to paint an idealistic vision of science (falsificationism) in contrast to how it's actually practiced; from SEP:
>Popper’s focus on falsifications of theories led to a concentration on the rather rare instances when a whole theory is at stake. According to Kuhn, the way in which science works on such occasions cannot be used to characterize the entire scientific enterprise. Instead it is in “normal science”, the science that takes place between the unusual moments of scientific revolutions, that we find the characteristics by which science can be distinguished from other activities.
I don't know about this specific case; I was only taking issue with the idea of pure falsificationism to distinguish science from pseudo-science. There are other demarcations (listed in the SEP article linked a few comments ago) which may also list the computational theory of mind as pseudo-scientific, but not just because it's unfalsifiable (if it really is).
That's not entirely correct. We don't know that a Turing machine can have conscious experience. There's no substantiated "in principle" explanation for that.
The definition of "a conscious experience" is so vague and circular that I'm not sure the question of "whether an X can have conscious experience" (where X is computer, dog, fish, human infant...) is even all that meaningful.
Either way we certainly don't have any indication that it is impossible in principle for a Turing machine to perform the same kind of calculation that gives rise to conscious experience in humans, or that this calculation would for some (supernatural?) reason not have the same outcome if performed by something other than a human brain.
> I'm not sure the question of "whether an X can have conscious experience" (where X is computer, dog, fish, human infant...) is even all that meaningful.
I do know that I have a conscious experience, so that's quite meaningful - to me. I cannot check that any other being has similar feelings, so the doubtful question would be whether "an X other than me can have conscious experience"; but people with good manners make the polite assumption that it's also true for other similar beings.
You may have the illusion of a "conscious experience" that is in fact a story told to yourself about how a thing you call "you" is in charge of your thoughts.
That doesn't really work. What is "yourself" in that statement, other than a conscious entity?
How would you write a computer program that "tells that story to itself," such that it actually has an experience of the world, as opposed to just being a machine executing a program without any conscious awareness?
Edit: also, whether we're in charge of our thoughts is a separate question from whether we possess consciousness. Even if we're not in charge of our thoughts, we still have a conscious experience of them.
I've never heard a complete and convincing explanation for what "yourself" could be, but meditating on the extreme unintuitiveness of self-reference and recursion (a la Douglas Hofstadter's I am a Strange Loop) increases my expectation that a computational explanation is coming, eventually.
I think that's pretty wishful thinking. It's not like we don't have a lot of experience with self-reference and recursion in computational systems. In fact this site is named after that. I don't think the Y combinator is conscious.
The conscious experience might be there but at the same time it could be an entirely deterministic thing. Maybe you and I having this exchange was determined in the instant of the big bang.
Being deterministic doesn't make it any less conscious. We're talking perception here, not free will.
In fact, there's pretty good evidence that what we call consciousness is a post-facto rationalization of the subconscious brain processes that determine an automatic answer of your brain to stimulus (not that it makes them deterministic, but certainly they're not "rational" in the classic sense).
"Your perception of conscious subjectivity" implies consciousness.
Put another way, how would you program a computer to have a perception of conscious subjectivity, as opposed to just blindly and unconsciously executing its instructions?
> "Your perception of conscious subjectivity" implies consciousness.
No it doesn't! Assuming by "consciousness", you mean a phenomenon that's not reducible to unconscious particle interactions, which is typically what is meant in philosophical discussions of this topic.
We have some mechanistic theories for consciousness [1]. It basically amounts to the same sort of illusion that your single core CPU uses to achieve the illusion of parallelism, ie. context switching between internal and external mental models produces the illusion of consciousness.
> Assuming by "consciousness", you mean a phenomenon that's not reducible to unconscious particle interactions
I'd say that's an unfounded assumption, which doesn't come up in the argument you're responding to - even if it's somewhat 'popular' elsewhere.
The argument made is that consciousness is (or includes) a form of perception; not that this perception is independent of mechanistic components. With this definition, you assertion that 'conscious subjectivity is an illusion' is inconsistent, as an illusion is a complex form of perception that requires a consciousness to perceive it.
Following your CPU example, there is parallelism from the point of view of the program being executed, even if it's simulated from a single-core mechanical basis (threads and context-switching).
> I'd say that's an unfounded assumption, which doesn't come up in the argument you're responding to - even if it's somewhat 'popular' elsewhere.
It's not really. Consciousness quite literally does not exist in mechanistic/eliminativist conceptions of consciousness like the link I provided, just like cars don't really exist because they aren't in the ontology of physics. My clarification of "assumption" is simply because many people don't know this.
> Following your CPU example, there is parallelism from the point of view of the program being executed, even if it's simulated from a single-core mechanical basis (threads and context-switching).
> just like cars don't really exist because they aren't in the ontology of physics
If I understand you correctly, that's a pretty harsh criterion for existence, isn't it? Even though a car is just a composite of metal atoms under a precise configuration and not a metaphysical entity on itself, you can still use it to drive you home. I suppose that makes me an utilitarian.
> No, there is concurrency but not parallelism.
You're right, my bad. I've forgotten my precision from my college days. Still, that's good enough for the program, just like my consciousness is good enough for me, even if it's entirely mechanistic and doesn't exist in the same way that cars don't exist.
Yes, but we don't know how to check that an entity has a conscious experience, so we can not falsify that a Turing machine has one, either. That's the whole reason for the Turing Test, btw.
Yes, we can't falsify that a Turing machine has conscious experience, but we have no reason or explanation to suggest that it does have one.
To come back to the original claim:
> Simple: Find something that the brain does that could not, in principle, be emulated by a Turing machine or equivalent. So far we don't know of any such thing
We may not "know" of such a thing with certainty, but we have a strong candidate in consciousness.
There are two possibilities here:
One is that Turing machines are conscious (and we're monsters for what we do with them), in which case we still have an unexplained panpsychic phenomenon which we would need new science to understand.
The other is that Turing machines are not conscious, in which case there's an unexplained phenomenon in how an object like the brain can give rise to consciousness. In that case, the question of whether a Turing machine could in principle emulate consciousness depends on what the cause of consciousness is. It's certainly possible, and doesn't even seem particularly unlikely, that we find that Turing machines cannot do this, and that something other than "computation" is needed.
> Yes, we can't falsify that a Turing machine has conscious experience, but we have no reason or explanation to suggest that it does have one.
I don't have no reason or explanation that suggests that you have a consciousness either. You could be a very elaborate chatbot that posts coherent replies at online forums. Also, I do know whether I'm a chatbot myself or not, but you can't tell about me just from the replies written here.
> We may not "know" of such a thing with certainty, but we have a strong candidate in consciousness.
The problem with that is, you don't have a test for consciousness. There's a strong candidate in MRI brain scans (at least for humans), but you can't really be sure.
