How? We can just as readily imagine a scenario where no vat-concept corresponds in any way with a trans-concept. — hypericin

True. In that case 'I might be a brain in a vat' does not refer to a brain or a vat as we understand them, which is Putnam's argument.

On Paris, yes, true. If the concepts correspond then there is a corresponding ambiguity. Vat-Texas is Trans-Vat-Texas.

You're equivocating. You know that right? — TheMadFool

I don't think so. In any ordinary sense, doubt is uncertainty; it involves calling something into question ("doubting" it); hesitating. Descartes was never uncertain about the existence of the desk he wrote on, or that of the pot he pissed in, or that of the other items he used every moment of his life. He didn't really ask himself "Art thou real, oh pot in which I'm pissing?" He engaged in an exercise, employing a faux doubt. He no more believed in a demon intent on deceiving him than you would believe that an enormous rodent dressed in a tuxedo typed the words you read.

It's not a thesis about what we are, but about what it is to know something. — Constance

Dewey as I understand him thought of knowledge as the result of inquiry. He thought it was an error to characterize each of our encounters with the rest of the world as a "knowledge" relationship or event, or as the result of a process by which we "know" something. When we see something we've seen thousands of times before we don't engage in reasoning in order to say we've seen it, or to see it. We recognize it. When we believe we undergo or engage in a process to "know" each time we perceive something, we misunderstand what we are and what the rest of the world is, and how we interact with it.

It's clear to me that Dewey thought ignoring context was a fundamental problem of philosophy. Reasoning, experimenting, is something we do to know something we don't already know--that's how we learn things about the world around us. But we don't do that all the time, because we don't have to. And the fact we do so or don't do so has nothing to do with the existence of the rest of the world.

As for Rorty, I think he departed from Pragmatism because he never accepted the respect both Peirce and Dewey had in method, specifically the scientific method and intelligent inquiry, as a means to resolve problems and questions, to understand and act. That's something I believe is essential to Pragmatism. No absolute truth, but "warranted assertibility" based on the best evidence available. This is what I think "saves" pragmatism from claims of relativism. Also, while Rorty thought Dewey was right to criticize metaphysics and metaphysicians, he also thought his effort at metaphysics was misguided.

What sets philosophy apart from other disciplines is its desire to know the truth at the level of basic questions, which is why all categories of thought are inherently philosophical regardless of way they differ in content. Going through your mail and doing quantum mechanics share that same foundation of structured thought and experience taking up the world. What does it mean at all to think, to solve problems, to experience pain and pleasure or art and music. Not this art or that love affair, but At ALL, how does one analytically approach those truly basic questions that are presupposed by all the things we say and do? — Constance

If philosophy is nothing more than our everyday experience and actions, then it is really nothing at all. At least nothing worth mentioning. You talk about philosophy consisting of analytic approaches to truly basic questions. Much, most, almost all of our daily experience is non-analytical, and good thing. It seems to me, without being able to point to specific evidence, that the only presuppositions to most of our daily experiences are more related to the structure of the mind than to analytic propositions.

Metaphysics? There is bad and good metaphysics. The former asks about, say, God's angels, actions, responses to sin, his kingdom, accessibility through prayer, God's omniscience, omnipotence, and so on, and so on. — Constance

I don't share your... prejudice against religion, but it has always bothered me that the existence of God is considered a metaphysical question. That's because the existence of a monotheistic God present as a conscious entity is a matter of fact, true or false. That takes it out of the realm of metaphysics to me. I think other aspects of Gods and religions are appropriate subjects for metaphysical discussion.

Empirical science? This is the naturalistic attitude. Philosophy is about what is presupposed by this, what assumptions are in place for this that make it possible to think and experience at all. Otherwise, you just doing scientific speculation, not philosophy. — Constance

Agreed, except I think that science has presuppositions beyond those for other modes of thinking and experience. If not, you've diluted the idea of metaphysics, including epistemology, to insignificance.

an object is a synthesis of overt, observable, features, and the contributions of the observer, and ponders the question as to whether there is any epistemic connection at all between out there and in here. — Constance

This is a metaphysical position. I think very few scientists have this kind of abstract understanding of what they do. Maybe I'm wrong.

What they usually do is take the naturalistic world, assume there is a connection, and simply move forward with that, putting aside any presuppositional objections. — Constance

This probably answers my question, although I thought the two statements were contradictory. I think I misunderstood.

Doing philosophy is not doing science, or, when a scientist does science, if she starts wondering about underlying philosophical issues, to that extent, she breaks away from her discipline. — Constance

I agree that doing philosophy is not doing science, but I don't agree that scientists don't need to understand underlying philosophical issues. Unless, I guess, you want to significantly limit the scope of science.

I've enjoyed this discussion. I am skeptical of the role you give phenomenology in your philosophy, but my understanding is based on reading summaries rather than primary sources.

There is my cat, and I know it, but how does, and this is the question of all questions, this opaque brain thing internalize epistemically that over there that is not a brain thing or any of its interior manifestations? — Constance

I strongly suspect this is not an epistemic act at all, but rather a distinction brains are hardwired to make. Witness organic brain disorders like schizophrenia where this distinction breaks down.

Instead of discarding as "bad metaphysics" what is called naïve realism here, why not instead bracket it with the disclaimer that this is not absolutely certain, but rather our best guess at the state of affairs. And describe why this qualifies as the best available guess (i.e. why brain in a vat can be cut away with Occam's Razor).

After all, whether or not we are envatted (love this coinage) is an empirical fact of the world, and empirical facts cannot, in principle, be proven with absolute certainty. All we can ever do is construct models which explain what we experience at the phenomenological level.

Absolute certainty is one of the great chimeras of philosophy.

Yes but there is a distinction between the world they present and the real world. This distinction is what the word "reality" delineates, without it the word has no meaning. — hypericin

I don't see how it applies to the BIV. 'Reality' is just a word which in the computer game case we're using to distinguish between the game world and the outside world. The word is embedded in a language, and act of social communication between two people, with a context and with intent. The word is being used to do something (in this case draw a distinction). It's not necessary to apply the exact same distinction to every single time the word is used, in every context. Language isn't like that.

So the language we use when describing a computer game doesn't tell us something about what is the case, it's not a window into the mind of God, it just a tool that gets a job done.

So the point with your BIV is that the situation would simply not be described by anyone in it as anything other than 'reality'. They wouldn't need another word because there's nothing to distinguish. There's no metaphysical truth being revealed here.

Insofar as an outside observer is concerned (maybe the only person in the world who isn't a BIV) their represented world would probably be called 'reality' and the simulation a 'simulation', but that would depend entirely on how useful whoever he was communicating with found the distinction to be and what language developed around that utility.

From our perspective imagining we're the non BIVs talking about the BIVs and wondering what word to use, I'd say 'reality' and 'simulation' would be a good choice.

From our perspective imagining we are the BIVs, 'simulation' would be a silly choice of word, it doesn't distinguish anything useful yet.

All we have from that perspective is that some of our representations come to us via an electrical signal from an electrode, others from an electromagnetic signal from a light wave. Why would we label one 'real' and the other a 'simulation' at that stage?

Are simulations observer dependent? That is to say, is it possible for a simulation to exist in a universe with no minds? — RogueAI

Again, dependent on language. 'Simulation' is a construct, amodel we make in our minds of some hidden states. Those hidden states, I believe, would continue to exist without minds, but there'd be no cause to distinguish them with the label 'simulation', because such a distinction can only be relevant to the models that minds make. I doubt an ant would have any use for such a distinction either, for example.

I agree with your analysis of language in general.

From our perspective imagining we are the BIVs, 'simulation' would be a silly choice of word, it doesn't distinguish anything useful yet. — Isaac

If we are participating in the thought experiment and imagining we are BIVs, then we must be imagining the world outside the vats. So then 'simulation' distinguishes our imagined vat world from the imagined world outside the imagined vats.

If we are participating in the thought experiment and imagining we are BIVs, then we must be imagining the world outside the vats. — hypericin

Tricky. None of us know the state of the world outside our Markov blanket, so we infer it. If we're BIVs (prior to any thought that we might be), then we infer the perception of a 'tree' in front of me is caused by some external state exciting sensory neurons. Aren't we in no different position once we become aware of the possibility of being a BIV? The assumption that the perception of a 'tree' in front of me is caused by some external state exciting sensory neurons, still holds. The 'external state' is just now an electrode (with perhaps a mad scientists at the controls), but the theory that some external state has excited some sensory neurons in such a way as to represent 'tree's remains unaltered.

It's only from the outsiders perspective 'seeing' the electrodes and the scientists, that these objects (electrode, scientist) are usefully distinguished from the objects they're causing to be represented in the BIV. From the BIV's perspective, they're the hidden external states they always assumed were there all along.

The 'external state' is just now an electrode — Isaac

Here I think 'external state' means light waves in BIS, electrode in BIV. But our analysis usually extends further than the immediate carrier of sensory information.

In BIS our mental model might be:
Tree -> reflected light -> eye -> brain signal -> perception of tree

But then supposed we imagine, or are convinced by, BIV. Then the analysis of looking at a tree might be:
Computer -> simulation software -> software state of tree -> electrode -> brain signal -> perception of
tree

But this is analogous to our model of say playing a video game with a tree in it:
Computer -> simulation software -> software state of tree -> screen emission -> eye -> brain signal -> perception of tree

In both the latter two cases our model of the object of our perception is that of a software construct, which is an aspect of software hosted on a physical computer. So in both cases it is linguistically meaningful and useful to designate the objects of perception as "simulations", as opposed to the rest of the physical world which hosts these simulations.

In both the latter two cases our model of the object of our perception is that of a software construct, which is an aspect of software hosted on a physical computer. So in both cases it is linguistically meaningful and useful to designate the objects of perception as "simulations", as opposed to the rest of the physical world which hosts these simulations. — hypericin

OK, I see where you're coming from. When I model, both the front ends are just 'Hidden State', so they're equal, to me.

One last fling...

Even in the last two, does it not really go;

Tree-> reflected light -> eye -> brain signal -> perception of tree (in the mind of the coder/programmer) ->computer -> simulation software -> software state of tree -> electrode -> brain signal -> perception of
tree (in the mind of the BIV).

Still coming from a tree, but going a long way round?

I strongly suspect this is not an epistemic act at all, but rather a distinction brains are hardwired to make. — hypericin

It makes sense to me that there are aspects of what we know that are not learned, but hardwired. On the other hand, the distinction between inside; what Constance calls "a brain thing or any of its interior manifestations;" and outside seems like something that would have to be learned.

He said without knowing what he was talking about. I really should do some more reading. Recommendations - science, not philosophy.

Even in the last two, does it not really go; — Isaac

Well you can analyze any number of ways. But these are models of a single perceptual event of a single object. Yours seems to mix this with a history of that object. Once the software is programmed and installed on the computer, the system is an independent object like any other.

But these are models of a single perceptual event of a single object. — hypericin

I think that BIVs are more significant for you, perhaps, for this reason.

I don't believe the object is out there in the 'real world' in the first place. I believe we construct the objects of our perception, so for me, the means by which the data we use for this construction arrives is of fairly minor importance.

But then what is your model of where these perceptions come from? Do you simply not have one?

But then what is your model of where these perceptions come from? Do you simply not have one? — hypericin

I believe the source of the data for each of my inferences is external to the model doing that inferring. I also believe that the source of the sensory data I model is external to me (everything I detect by interoception). That's about as far as it goes.

Dewey as I understand him thought of knowledge as the result of inquiry. He thought it was an error to characterize each of our encounters with the rest of the world as a "knowledge" relationship or event, or as the result of a process by which we "know" something. When we see something we've seen thousands of times before we don't engage in reasoning in order to say we've seen it, or to see it. We recognize it. When we believe we undergo or engage in a process to "know" each time we perceive something, we misunderstand what we are and what the rest of the world is, and how we interact with it.

It's clear to me that Dewey thought ignoring context was a fundamental problem of philosophy. Reasoning, experimenting, is something we do to know something we don't already know--that's how we learn things about the world around us. But we don't do that all the time, because we don't have to. And the fact we do so or don't do so has nothing to do with the existence of the rest of the world.

As for Rorty, I think he departed from Pragmatism because he never accepted the respect both Peirce and Dewey had in method, specifically the scientific method and intelligent inquiry, as a means to resolve problems and questions, to understand and act. That's something I believe is essential to Pragmatism. No absolute truth, but "warranted assertibility" based on the best evidence available. This is what I think "saves" pragmatism from claims of relativism. Also, while Rorty thought Dewey was right to criticize metaphysics and metaphysicians, he also thought his effort at metaphysics was misguided. — Ciceronianus the White

Rorty is a post modern philosopher, which sets him apart from the old school of pragmatism, and this means he is looking at language and vocabularies as the foundational discussion about the world. Dewey and the rest did not think in terms like this, but what I think is the essence of pragmatism is what connects them, and this is in the scientific method, which is the foundation: the hypothetical deductive method, making the basic structure for thought and Being the conditional proposition, If...then....What is the concept and the proposition reducible to? What works. Look at what Rorty says about contingency:

For Kant and Hegel went only halfway in their repudiation of
the idea that truth is "out there." They were willing to view the wodd of
empirical science as a made wodd - to see matter as constructed by
mind, or as consisting in mind insufficiently conscious of its own mental
character. But they persisted in seeing mind, spirit, the depths of the
human self, as having an intrinsic nature - one which could be known by
a kind of nonempirical super sciencecatled philosophy. This meant that
only half of truth - the bottom, scientific half - was made. Higher truth,
the truth about mind, the province of philosophy, was still a matter of
discovery rather than creation.

He goes on to emphasize that any such "discovery" notion is shear metaphysical nonsense. Consider how this goes: If you think there is something "out there" that our knowledge is telling us about, that this aboutness that we have as our knowledge condition includes actual features of that object of knowledge, then you haven't understood pragmatism's unavoidable "truth" structure, viz, that all the understanding every has, is the pragmatics. On the ontological end, it is just familiarity, reified familiarity, so in the end, the present moment , that very powerful sense of reality and presence one has about the cat being on the couch, the couch being blue in color, and so on, is a synthesis of the pragmatic conditions that give knowledge that famous forward-looking anticipation about what a thing does, the If.....Then.... conditional structure, and the simple "presence" that is familiar (habitual beliefs, says Dewey) since childhood.
The difference between Rorty and the traditional construal is focus on language, which makes him a post modern pragmatist. And what is language? Language is a pragmatic construction that is foundational for our "being in the world" and it is not as if Dewey actually talked like this, I don't think he did (reading through Nature and Wxperience. I have read others, like Art As Experience, some works on education, others? Don't recall), it's just that post modern thinking puts the burden of the real to language's language's interpretative nature, but giving full due to the things Dewey thought essential to a comprehensive accounting of the world, the non cognitive dimensions of affect, desire, motivation, fantasy and imagination and so on. Note that that Rorty's pragmatism, following Heidegger (if you like pragmatism, Heidegger's Being and Time is the perfect existential counterpart), makes the everydayness of the world and all of its affairs equal in their descriptive relevance, but when it comes to talking about what all this is, philosophy, then all eyes are on language and its meanings, as so an analysis of language is paramount.

I guess you're right, and Rorty does not follow Dewey and Peirce, but he does follow through on them in post modern themes. And there is no room at all for any positing an exteriority apart from experience, apart from t he language and logic that construct thought. The thoroughgoing pragmatic position cannot support any notion what ever of an "out there" to things discovered in experience.

I don't believe the object is out there in the 'real world' in the first place. I believe we construct the objects of our perception, so for me, the means by which the data we use for this construction arrives is of fairly minor importance. — Isaac

Wouldn't it be important for figuring out the truth of your model of perception? If you're a BIV, then you're not perceiving anything. It's all a generated hallucination based on whatever the programmer wants you to believe you perceive. You don't have any sensory organs, so it can't be a perception.

If you're Kantian, then your model of perception is entirely empirical. Who knows what the act of perceiving in-itself actually is.

If you're a BIV, then you're not perceiving anything. It's all a generated hallucination — Marchesk

That's what perception is. https://link.springer.com/chapter/10.1007/978-3-030-42986-7_5

So perception isn't veridical, rather its a hallucination controlled by the world based on the brain estimating what's out there, which is updated from the stream of sensory information?

So perception isn't veridical, rather its a hallucination controlled by the world based on the brain estimating what's out there, which is updated from the stream of sensory information? — Marchesk

Yeah. But we want to minimise surprise, so a good match between the probability function of the model and the distribution of the hidden state is something we evolve toward, purely by energy efficiency.

Also we're a social species, we invest quite a lot in making sure your model matches my model to a good degree of similarity.

Also we're a social species, we invest quite a lot in making sure your model matches my model to a good degree of similarity. — Isaac

The trouble is that under the view that, "all perception is generated hallucination", other people, your own body, and the wider world around you is itself included in this generated hallucination. Essentially your perceptual 'world', which includes your own body, and other people, functions as a sort of internally generated self/world model, which is theorized to be caused by the brain/nervous system of something unknowable ("hidden state"). Its a kind of solipsism.

But we want to minimise surprise, so a good match between the probability function of the model and the distribution of the hidden state is something we evolve toward, purely by energy efficiency. — Isaac

I would imagine a "good match" (I don't even know how a good match would even be possible between hallucination and the unknowable..) is irrelevant in terms of our evolution, and the content of our 'hallucinations' would evolve towards what is useful in an evolutionary context (survival, gene replication, etc).

Essentially your perceptual 'world', which includes your own body, and other people, functions as a sort of internally generated self/world model, which is theorized to be caused by the brain/nervous system of something unknowable ("hidden state"). Its a kind of solipsism. — Inyenzi

I'm not seeing the 'trouble' you started out claiming was there.

I would imagine a "good match" (I don't even know how a good match would even be possible between hallucination and the unknowable..) is irrelevant in terms of our evolution, and the content of our 'hallucinations' would evolve towards what is useful in an evolutionary context (survival, gene replication, etc). — Inyenzi

You may well imagine that, yes.

If one’s identity is expanded to include the entire body, beyond the surface of the brain and nervous system to the surface of one’s skin, observation of the external world is direct. There is no longer some medium or veil between perceiver and perceived.

If philosophy is nothing more than our everyday experience and actions, then it is really nothing at all. At least nothing worth mentioning. You talk about philosophy consisting of analytic approaches to truly basic questions. Much, most, almost all of our daily experience is non-analytical, and good thing. It seems to me, without being able to point to specific evidence, that the only presuppositions to most of our daily experiences are more related to the structure of the mind than to analytic propositions. — T Clark

Look at it like this: Philosophy asks the most basic questions. About what? Everything. Then what are basic questions? Questions that underlie everything. They sit quiet as assumptions in a place that gives all knowledge claims there foundation. The technical side of philosophy lies in the disciplined body of theory and inquiry regarding all things at this foundation. E.g., the way analytic philosophy goes after the givenness of the world lies with Dennett's "pumps" that examine qualia to see if the term makes any sense. Where do we get this qualia idea? From ordinary experience. Continental philosophy handles it much differently, but the source is always everydayness, Heidegger's "always, already there" that is the starting point of any inquiry: our everydayness is the beginning of any philosophical question.
Of course, there is that nagging history of metaphysics that plagues inquiry, but everybody wants to be rid of this. Nietzsche blames it on Christianity, Kierkegaard on Christendom, Heidegger on the Greeks, Dewey on rationalism, and so on.

I don't share your... prejudice against religion, but it has always bothered me that the existence of God is considered a metaphysical question. That's because the existence of a monotheistic God present as a conscious entity is a matter of fact, true or false. That takes it out of the realm of metaphysics to me. I think other aspects of Gods and religions are appropriate subjects for metaphysical discussion. — T Clark

It depends on what you mean by religion. If you are talking about the an anthropomorphism that has a will, a wrath, who is king of all and bows to no one, who insists on obedience, who does this and that like people do, then religion is just interpretatively superfluous, to put it nicely. You know, a lot of narrative accounts that fill an empty space that needs filling. But if you mean the jumping off place where the "totality" of our understanding leaves off and all that is meaningful and important is left hanging for want of a foundation, then I can think of nothing more important than religion. Metaphysics is now real, I claim. But where does it make its appearance? In experience. For example, in the question, Why are we born to suffer and die? Such things are handily dismissed in philosophy given that no empirical answer shows up and Wittgenstein made it clear language cannot talk about value. But then (See Critchley's very interesting account in his Very Little....Almost Nothing) there is something powerful and profound about the question, for once the context is taken out of familiar contingencies, you know, explanations that rest with science, with evolution (suffering is conducive to survival), with biology, with historical narratives, and so on, all of which fail entirely because they beg the ultimate question where Why?, then one is without context, and dreadful suffering simply sits there, and expression of Being, a reality not generated by language and culture, but by the "world" itself, THEN religion becomes a very different affair. This I call good metaphysics, this standing at the threshold (See Levinas' Totality and Infinity: the idea that is exceeded by the ideatum; the desire exceeded by the desideratum) is, well, beyond merely humanizing. There is deep philosophical discussion that brings this to light. John Caputo's Weakness of God and his Prayers and Tears of Derrida; and there is the recent French theological turn with Michel Henry, Jean luc Marion and others. These play off Kierkegaard's Concept of Anxiety, as does all existential philosophy.

Agreed, except I think that science has presuppositions beyond those for other modes of thinking and experience. If not, you've diluted the idea of metaphysics, including epistemology, to insignificance. — T Clark

Not sure what other modes of thinking would be. As I see it, science is in all we do and think, for it is at the basis for understanding. I am referring to the scientific method, the conditional proposition, if....then that is the structure of thought itself. This may sound odd, but one has to consider that the world is Time, it is Heraclitus' world, so a thought is a temporal event, and so its analysis looks at a beginning, a middle and an end. Dewey called this the consummation. All knowledge is consummatory. Ciceronianus the White, above, thinks like this.

This is a metaphysical position. I think very few scientists have this kind of abstract understanding of what they do. Maybe I'm wrong. — T Clark

I think they don't care, and the matter is alien to their concerns. If pressed, they would have to concede, would then dismiss it. Most analytic philosophers hold with Wittgenstein: philosophy simply has nothing to say about it. The world doesn't rest on metaphysics, for metaphysics is just nonsense talk. I haven't read anything lately from this side of things, but I suspect nothing has changed. Obviously, they are mistaken.

To me it is not abstract at all. Two people face to face in conversation. "Between" them is palpable mystery. Metaphysics has to be seen this way, and the way for this is in the concept of "presence" or "givenness". The infamous phenomenological reduction of Husserl. See is his Ideas I, his Cartesian Meditations. Then Eugene Fink's Sixth Cartesian Meditation. Extraordinary, these are.

I've enjoyed this discussion. I am skeptical of the role you give phenomenology in your philosophy, but my understanding is based on reading summaries rather than primary sources. — T Clark

I apologize for all the philosophers I threw out at you. But they are what I think. These guys are simply too interesting not to mention. Phenomenology is, as I see it, the only wheel that rolls in philosophy.

I strongly suspect this is not an epistemic act at all, but rather a distinction brains are hardwired to make. Witness organic brain disorders like schizophrenia where this distinction breaks down.

Instead of discarding as "bad metaphysics" what is called naïve realism here, why not instead bracket it with the disclaimer that this is not absolutely certain, but rather our best guess at the state of affairs. And describe why this qualifies as the best available guess (i.e. why brain in a vat can be cut away with Occam's Razor).

After all, whether or not we are envatted (love this coinage) is an empirical fact of the world, and empirical facts cannot, in principle, be proven with absolute certainty. All we can ever do is construct models which explain what we experience at the phenomenological level.

Absolute certainty is one of the great chimeras of philosophy. — hypericin

Best guess is the way of philosophers like Searle, and, as far as I've read of analytic philosophy, it is dismissive merely. It is hard to put this into a paragraph, but analytic philosophy, grounded in the assumption that meaningful language ends where clarity ends (a positivist leaning) altogether misses the point of philosophy. There is no Wittgensteinian hard line between facts and nonsense. Rather, the world is fluid, thought and its experiences bleed, if you will, together in the known and the unknown, and this can lead to bad metaphysics, which is all too clear to require explaining, but Good metaphysics is a different matter. It is what emerges out of the attempt to move beyond a long history careless thinking, and to discover what is there, in the world, presupposed by all of this and is the foundation of it. Wittgenstein loved Kierkegaard! And Kierkegaard is the father some very penetrating metaphysics.

And what is there at the "phenomenological level" you mention? This is the question. What is there in the everydayness of our world, analytically inaccessible because foreign to familiarity? Husserl's epoche, in a letter he wrote, is said to have inspired students to join the church. He was no metaphysician (putting aside complaints later on), but simply wanted philosophy to to return to the "things themselves" and it was Husserl who brought matters to the phenomenological level. What can be religiously inspiring about this very rigorous (see Husserl's Ideas I and II. His Logical Investigations I haven't read much of. But The Idea of Phenomenology opens his later thought) and "scientific" (not empirical) turn? The answer is that it brings attention to the world apart from the empirical explanatory models as a qualitative move, that is, a very different content. This suspends all knowledge claims that would otherwise take hold, which he labels the "naturalistic attitude". What rises out of this is existentialism, aka, phenomenology.
As far as absolute certainty goes, then concept itself is chimera, and while logical necessity (certainty) certainly is there, clearly a structure of meaningful utterances (all logic is tautology, say Witt) one has to see that this and actuality run on a collision course (Kierkegaard). Logic words like certainty do not possess the world, but are an essential part of institutions that pragmatically take up the world. The world, its loves, hates, passions, motivations, compulsions, miseries, joys, and so on, are NOT tautological constructions. They are actual, not eidetic, merely, and this actual world is our metaphysics (of course, the same holds for logic itself: unknowable in its generative source, for, as Witt tells us, it would take logic to conceive of this source, which begs the question).

If one’s identity is expanded to include the entire body, beyond the surface of the brain and nervous system to the surface of one’s skin, observation of the external world is direct. There is no longer some medium or veil between perceiver and perceived. — NOS4A2

This, of course, moves along with the assumption of physical science. So, there is this cat thing over there, and my brain thing here, and my awareness extends all the way to the outer edge of my skin. Pls proceed to explain how it is that my cat gets "in" the brain thing. Note that the moment you begin explaining how the electromagnetic spectrum is of different wavelengths, some are reflected, others absorbed in a given material, in this case, the fur of my cat, I have to stop you: How did you brain thing come to understand those electromagnetic spectrum wavelength things, and how did THEY get in the brain thing?
All references to out there, are really references to events "in here". It is not that there is no out there; the question is, how is it possible to make this claim?

Pls proceed to explain how it is that my cat gets "in" the brain thing. — Constance

Viewing humans as living organisms in an environment (which is what we are, I believe), I can't help but think this is tantamount to asking someone to explain how our food gets into our stomachs.

The assumption is that something exists between perceiver and perceived, that some kind of medium makes what appears to be direct observation of the world, indirect observation. So what is it exactly that prohibits you from directly observing the world? What is it, exactly, that exists between you and what you perceive?

Viewing humans as living organisms in an environment (which is what we are, I believe), I can't help but think this is tantamount to asking someone to explain how our food gets into our stomachs. — Ciceronianus the White

I see, but don't you see the difference? It would be as if explaining how food get in the stomach included an explanatory dead zone, and so there would be nothing to say. Explaining how the cat gets into a brain, BEGINS with a brain phenomenon, not with some affirmation of something that is not a phenomenon. The cat out there the knowledge of which you are trying to explain is not a phenomenon, but is supposed to have an existence beyond phenomena, something there that is discoverable to which you knowledge has found access. But how can this discoverable thing every make its way into that which makes it into a phenomenon, when to affirm this would require you to affirm what-is-not-a-phenomenon? How can a phenomenal system affirm what is not a phenomenon? Or even make sense out of such a thing? All thinking, causality, anything posited at all, is a brain event, so even when you start talking about electromagnetic waves being absorbed or reflected by the cats fur, you are stopped right there: How does light and its properties ever make it into the explanatory matrix of a brain? to be used to explain how the cat gets "in there"?
There is simply no non question begging way to affirm this.

The sticking point of the BiV thought experiment is that we can stimulate specific combination of neurons in ways that mimic to a T actual experiences. For instance, I could apply an electrical current to the pressure & temperature sensors in your hand and give you the feeling that you're holding a hot cup of tea. There is no hot cuppa! A little extrapolation and you can now think yourself as a nothing more than a brain in vat whose entire reality is simply a supercomputer causing specific combinations of neurons to fire. Like the cuppa isn't real, neither is the world the brain perceives.

I recall pointing out once in another thread roughly half a year ago that there's only one thing we can be absolutely certain about - mental experience. The so-called physical world could be an illusion/ a simulation. Compare that to how there's no plausible way we could cast doubt of a similar nature regarding the mind. To doubt the mind is to admit there's mind; how else can you doubt it?