You don't even need to bring science in to the equation. You can just note the interdependence of everything in the world from a phenomenal point of view. — Marchesk

But you’re still speaking from a realist perspective - whether scientific or not.

The whole point of so-called ‘idealist’ arguments is to turn the attention back on the very act by which we know, see, and perceive. From a realist perspective, what happens when we see the proverbial tree or chair or whatever object? You know the story - light is detected by the retina, the brain synthesises that information then interprets it, names it, and so on - ‘it’s a chair’.

The idealist will ask, well what is ‘the object’ apart from that interpretive act? How do you get ‘outside’ the sensory and intellectual system to see what the object ‘really is’? Because what you’re actually reporting on, is an impression, idea, or perception - that is how knowledge is constituted.

The clearest statement of this argument are the opening paragraphs of Schopenhauer’s WWR. But I think it’s a mistake to imagine that Schopenhauer is saying that ‘the world disappears when I’m not looking at it.’ This, again, presupposes a point of view, a perspective from which that non-existence would be seen.

But that is not what ‘the idealist argument’ is really saying at all. It is really an argument about the nature of knowledge, experience and consciousness - how we know what we know. Our knowledge and experience is actually constituted, made up of different facets, all of which come into play when we see ‘the object’. And they are therefore constitutive of whatever we know of reality. That’s the sense in which reality is ‘dependent on perception’. Not that all the planets around unknown suns don’t exist until they’re literally being perceived. What’s important about the argument is that it reminds us that we really are part of the picture - you can’t imagine anything from absolutely no perspective. Whereas science assumes that the universe that it sees and measures exists entirely independently of the scientist. But it doesn’t! (This is what came out of the ‘observer problem’; read this.)

I know how hard this is to get - it’s a basically a gestalt shift. Like, someone once showed me one of those ‘magic eye’ books, where there are two apparently random patterns, and if you hold them a certain distance from your face, you will suddenly see a three-dimensional image. It never worked for me.

If the train wheels ceased to exist once nobody was looking at them, the passengers would hear and feel an almighty jolt... — andrewk

That example is verging on facetious, insofar as what it really does is shows that Moore doesn’t understand idealist arguments, or rather that they don’t mean what he takes them to mean.

(This is what came out of the ‘observer problem’; read this.) — Wayfarer

Read it just now.

The most interesting, informative article I have read in a while.

But you’re still speaking from a realist perspective - whether scientific or not. — Wayfarer

Well, Berkley had the same sort of perspective in that he didn't saysay the light bouncing off a flower into your eye is an interpretive act. Rather, the omni-observer, God, is around to keep the rest of the world there as we would have perceived it.

By idealism you mean the Kantian variety where what is perceived might be entirely different than what caused the perception.

ur knowledge and experience is actually constituted, made up of different facets, all of which come into play when we see ‘the object’. And they are therefore constitutive of whatever we know of reality. That’s the sense in which reality is ‘dependent on perception’. — Wayfarer

But if you don't want to this to collapse into skepticism, you have to allow that our perceptual facilities do provide some accurate information about how things really are.

Why would we have eyes to see if what is seen isn't what's really there? That doesn't mean our senses gives us a completely accurate view of the world. They don't (and sometimes they mislead us). But you don't have to go all the way to the other extreme and say we can't know anything about the external world, trapping us inside the veil of perception (and interpretation).

Either science can be done on the world despite our perceptual limitations, or the ancients skeptics were right. I think given the huge success of science that the skeptics were premature in doubting so thoroughly.

But if you don't want to this to collapse into skepticism, you have to allow that our perceptual facilities do provide some accurate information about how things really are. — Marchesk

It’s worth recalling that Kant was a polymath who lectured in science as well as many other subjects, and whose theory of nebular formation is still current science. That was the point I was making about him being an ‘empirical realist’, something which he himself says.

Why would we have eyes to see if what is seen isn't what's really there? — Marchesk

What the eyes see is only part of the story. That is the point. Obviously science works - we wouldn’t even have this platform to exchange ideas on, if it didn’t. But it too is only part of the story. And you can be sceptical about science without reverting to the Stone Age. The whole problem of ‘scientism’ is that it says that science knows everything that can be known, in principle. That is the point of this debate as far as I’m concerned. (If you have a moment, do have a look at this excellent article on the continuing relevance of Kant. Says in a couple of pages what might take years to study.)

The whole problem of ‘scientism’ is that it says that science knows everything that can be known, in principle. — Wayfarer

Who says this? Every scientist I've ever spoken to in my career has been of the opinion that science produces those ideas which represent testable theories which require the least new phenomena and clash least with existing theories. I've never heard anyone claiming it 'knows' all there is to except, wishy-washy theists who want to make a straw man out of it.

What positivists, and those following on from some of their approach, are saying is that metaphysical discussions, where they take place, are for determining that which can be established by empirical verifiable testing, and that which cannot. That which cannot then is meaningless in epistemological terms. It might be meaningful aesthetically, or psychologically, but it has no meaning as far as knowledge is concerned. It is absolutely not saying that we can dispense with all the things that fall into this category, nor is it saying that everything that does not can be proved to be unquestionably right. Just that it is not meaningful to talk about those things that do not in epistemological terms.

As far as this topic is concerned, if we restrict ourselves to empirically verifiable evidence, then we can verify the existence of the paper by the means Marchesk has already outlined. We can then discuss the extent to which those means cover all that is possible. Beyond that, there is only an aesthetic purpose to any further speculation because nothing can ever be known with any public utility beyond that.

Because it's there when you reenter the room and open the desk. — Marchesk

It does not follow from the fact that the paper is there every time I look, that it is there when I am not looking.

you can set a camera to record a video or snapshots of the paper while you're away. — Marchesk

This demonstrates the existence of the paper when recorded - recording really just being a sort of extension of our perceptual abilities. What about when the paper isn't being recorded? I surely believe that it exists whilst being unrecorded and unperceived. But how can I know it? Hence, the camera suggestion does not really help (I failed to realize this in a previous thread, and the discussion became confused as a result).

If you look up at the sky, is the ground still holding you up? — Marchesk

I can feel the ground under my feet so there is no problem here.

How far do you want to take the skepticism? Because it can go all the way to the current perception for me right now, and leave everything else as unknowable. — Marchesk

I want to take the scepticism this far and no further: any belief of mine for which there is no reliable method of establishing it, is one I shall doubt. I stress, as I did in the OP, that I am not demanding certainty or that all beliefs be capable of proof to any reasonable person. I am merely requiring that there me some method which is such that, when used correctly, produces beliefs which are more likely than not true. I don't think this is taking scepticism too far at all. To expect anything less is to believe things which are not even probable - guess work.

Let's say that when nobody is observing the rest of the universe, all that matter is destroyed. So you get in a car while nobody is doing astronomy, and the driver steps on the brakes. What happens? Do you feel the rest of the universe opposing your change in motion, or just the Earth and Sun and maybe Venus if it's up? — Marchesk

I see what you are saying, but I think there are problems. When the driver steps on the breaks, what I observe is the car slowly coming to a stop. I do not feel 'the rest of the universe opposing my change in motion'. Maybe there is no 'rest of the universe' at that moment. I realize that a scientific account of what happens when the driver presses his breaks obviously requires the existence of a significant part of the universe, but does that account prove that things exist unperceived or does it merely assume it? The account would need to be fleshed out further before I could say.

Here's another related way to go about this. Has anyone died from something unperceived? Yes, quite often. One example would be going on a hike and being killed by a falling rock. The hiker may not have seen or heard the rock. — Marchesk

The example isn't fleshed out in enough detail for a fair assessment. The hiker didn't see the rock, but did any body else see it? If so, then the example is compatible with things only existing when perceived. If nobody saw the rock hit the hiker, not even the hiker (perhaps he was asleep), then how can anybody say with any degree of reliability that the rock actually did hit him? This hasn't been explained.

Another would be dying from some disease, particularly in the past or places without access to medical equipment. You get sick and die from something nobody perceives. How does that work if the microbes, cancer, etc. doesn't exist? — Marchesk

What killed me are the microbes, and ex hypothesi, nobody perceived the microbes while they were killing me. Again then, how can anybody say with any degree of reliability that the microbes did kill me? It seems to me that typically this would be explained by a classic kind of causal inference. We perceive the person suffering various symptoms. We perceive the existence of microbes which we did not perceive before they got sick. We also perceive that as the symptoms worsen the number of microbes (for example) increases and their spread throughout the bodies crucial organs grows wider. We might infer that the best explanation is that the microbes do something to cause the symptoms and the eventual death. This can be further supported by other observations of the microbes behaviour on isolated tissue, and so on. In short, the microbes are observed to exist at certain times in conjunction with certain symptoms and in a certain patterns. When the symptoms are perceived on a different occasion, it is inferred that the microbes are again there.

But now return to the paper in my desk. How could this argument be run for that paper? I am hopeful, but not sure. Your further questions about digestion and intestines are the same. Does digestion happen when no one is perceiving it? Perhaps an argument like that I gave for microbes could be given. Although I'm not sure exactly how it would go. I made the thread hoping someone would explain how the argument would go, not simply restate my question with different examples!

By observing their actions such as dogs reacting to higher frequency whistles or homing pigeons. — Rich

That is, obviously, when you are observing them, not when you are not observing them.

However, if they stoped existing, everything would necessarily change since you are literally taking something out of existence. — Daniel

I don't understand why this has to be the case. Isn't it conceivable that you exist just as you now do exist without the existence of a collection of atoms completely distinct from you? It might be true that scientifically speaking, to remove certain atoms from the world all together would cause a change in everything else (though I am not sure about this), but that presupposes the whole atomic theory and causation, and both of these presuppose that things exist when unperceived.

You probably won't know, because of the crudity of human sensory organs, but in theory you could, in the same way as we know about a black hole: by its interaction with other things. A paper sheet in another room interacts with the desk drawer containing it, which interacts with the desk, which interacts with the floor and air, which interact with the walls of the closed room, which interact with the air outside the room, which interacts with you,

There would be tiny differences in the patterns of air movement around you if that piece of paper were not in that closed desk in the closed room. Your naked senses may not be enough to measure that but, at least in theory, if you had sensitive enough measuring equipment, you could detect the difference.

This is writ large in Wayfarer's / Russell's / GE Moore's example here (↪Wayfarer). If the train wheels ceased to exist once nobody was looking at them, the passengers would hear and feel an almighty jolt as the carriages they were in suddenly dropped onto their axles.

This response may not work for astronomical objects outside the observable universe, because of the expansion of the universe. But that's a somewhat different discussion. — andrewk

Thanks for the interesting answer.

Let us use the train example because having it writ large is a little easier. You say that if the wheels ceased to exist when unperceived, the carriages would drop onto the axles and the passengers would feel this. But this answer assumes that gravity continues to operate while unperceived does it not? W.T Stace first pointed this out in connection with a fire. Does a fire continue to burn even when no one is looking? A critic of Stace had said that it must do so, because when you return to the fire after ten minutes, the wood has turned to ash, which is just what happens if you stay and watch the fire burn out. Stace pointed out that this argument assumes that the law of causation operates continuously through time, whether observed or unobserved, and this is obviously part of what needs to be proven. The same can be said, seemingly, of the train example. That the carriages would fall onto their axles if the wheels didn't exist while unobserved assumes that the law of gravity continues to operate when unobserved, and this is part of what has to be proven.

This said, I suspect that there is a mistake in Stace's reasoning here - and so also with my reuse of it, but I don't know what it is.

Thanks to everyone for thorough replies

I'd also like to thank specifically, because I didn't address any of his/her points directly. This isn't because I don't appreciate the posts. Quite the opposite, I find them very insightful and the links provided equally informative. I do disagree with you Wayfarer, if you think, as it seems you do, that the view that the train wheels stop existing when no one is observing them is a silly view which only someone who misunderstands the issue - like you say Moore does - would discuss. I think this matter is not as clear as that, as I have tried to explain. I recommend W.T Stace's Refutation of Realism. Stace defends the view that 'nothing exists except minds and their perceptions', where this is taken quite literally and has the consequence that the train wheels do not exist when unperceived.

As to your suggestion that Kantian Idealism is about 'how we know what we know', the question depends on the word 'know' which is intolerably vague, and so it is hard to assess how Kantian Idealism is an answer to that question without an explication of 'know'.

Best,
PA

That is, obviously, when you are observing them, not when you are not observing them. — PossibleAaran

The question I thought was how do we know that there are things out there that we are not overseeing directly. My answer is by observing indirectly - that is overview the actions of other life forms.

Subjective idealists rightly insist that our definitions of physical objects must in some way semantically reduce to our observations and interrogative practices, such that "to be is to be perceived" is a logical truth.

Realists are right to point out that subjective idealists are naive if they think that the semantics of physical objects reduce to atomic acts of perception.

Once realists and idealists recognise the semantic holism in our translation of observations into causes and vice versa, they ought to realise they are speaking past one another and making complementary arguments.

, when looking at your piece of paper, put your hands in front of your eyes so you no longer see it.
Now move your hands away again.
1) Did the paper disappear? 2) Did a goat appear where it was? 3) Do you see the paper again?
(The former two may be evidence of David Copperfield playing tricks.)
Wouldn't it be neat, if, say, a piano was falling down towards you, and you could look away, et voilà, the piano would no longer exist? :)
Bit like that old story of ostriches sticking their heads in the sand when they see something scary.
The most parsimonious line of thinking seems to degenerate into solipsism (or similar idealism), something like that. (N)

Do we know that anything exists when unperceived? — PossibleAaran

The issue might be best understood from a temporal perspective. Consider that the human being is endowed with a very particular temporal perspective. Average reflex time is about a quarter of a second, so let's say that our perspective of what is "present", or "now", is about a quarter of a second. However, we can imagine time periods as short as a Planck time, and as long as billions of years.

Because everything in the world is moving, how things appear to our senses, is determined by our temporal perspective. Things moving very fast like photons only appear as a bright blur, because in that quarter second of perspective time, they cover a great distance of space, and must appear to be in all of those places at the same time (that quarter second which is "now"). Things moving much slower can appear to have a fixed position in that quarter second temporal perspective.

Now imagine different temporal perspectives. Suppose "the now" was a year instead of a quarter second. The earth covers the entire area of one orbit and so it now appears like a ring around the sun from this perspective. If we extend the perspective of "the now" to a longer and longer time period, like billions of years, the moving bodies in the universe occupy the entire space of the universe, and the universe appears like one solid entity, one thing.

So the existence of "things" is really dependent on a subject, an observer who has a particular temporal perspective. Our inclination is to ask, what would the universe look like from the temporal perspective of the subject, if we remove the subject, the observer. Will things still be the same? But this question really doesn't make any sense, because the temporal perspective is the property of the observer, and to remove the observer is to remove that temporal perspective. So to ask what would the universe look like from the temporal perspective of the observer, without the observer, is still to reference the observer. Without referring to the temporal perspective of the subject, we'd have no principle to choose a temporal perspective. Any choice of temporal perspective would be arbitrary, and the way that things appear, since they are all moving is dependent on the temporal perspective.

If we completely remove the observer, then we have no particular temporal reference, only the entire universe for all of time. There is no basis for singling out this particular time or that particular time. We'd be inclined to say that there would still be "the universe", without any subject or observer. But we really do not know what it means to be a universe, so this statement doesn't really make sense either. In the end, we have to face the fact that this question, "does anything exist if unperceived", really doesn't make any sense at all, because "to exist" refers to how we perceive things.

does anything exist if unperceived", really doesn't make any sense at all, because "to exist" refers to how we perceive things. — Metaphysician Undercover

However, careful examination of our existence provides clues.

When we are unconscious, we are not observing. And then we awaken!

How do we know that we were unconscious or asleep? Because there had been some disruption in our memory pattern. Something is different than it normally would be. We surmise that we had been unconscious.

Some memory has changed (or been disrupted). Other patterns remain. This is evidence of a changing universe with patterns.

How would the universe be without an observer? It would be as if we are unconscious. Are there persistent patterns embedded in the universe? Appears so, as they persist through an unconscious state. A holographic model of the universal memory supports these experiences as we perceive them. Memory is in the fabric of the universe. That is what we (our minds) are observing.

The whole problem of ‘scientism’ is that it says that science knows everything that can be known, in principle.
— Wayfarer

Who says this? — Pseudonym

Sounds rather like this, doesn’t it?

Our experience is what it is, it's just that we don't know 'what it is' yet. If 'what it is' is nothing more than the firing of neurons, then scientific investigation reveals the whole of it, there is nothing more to investigate. — Pseudonym

In the end, we have to face the fact that this question, "does anything exist if unperceived", really doesn't make any sense at all, because "to exist" refers to how we perceive things. — Metaphysician Undercover

I think this fundamentally confuses how we come to know about the world with the way the world is itself. Just because we can't get outside ourselves to imagine exactly how the world is without us observing it does not entail that the world cannot exist without us perceiving it.

It can simply be a limitation on human imagination. But even then, we do possess powerful abstraction capabilities so that we can model the universe mathematically without any observer. We do have a theory of general relativity that deals with that.

Wouldn't it be neat, if, say, a piano was falling down towards you, and you could look away, et voilà, the piano would no longer exist? — jorndoe

Exactly. If you look away from a falling rock, does it cease to exist until it crushes you, and then goes back to not existing once you die? What if you don't have time to experience the crushing? Does the non-existent heavy object not cause you to cease to exist?

But this answer assumes that gravity continues to operate while unperceived does it not? — PossibleAaran

This is a subject dear to my heart, because of my perplexity over whether I will ever do a bungee jump (and whether I 'should'). (I suspect I won't, my excuse being the risk of detaching a retina).

You know that terrible feeling you get in your stomach when you jump off the diving board? I find it terrifying, yet I seek it out, jumping off (low) bridges into water, doing vertiginous waterslides, roller coasters etc.

That feeling is exactly what 'not perceiving gravity' is. It feels like there's a force, but actually it's an absence of force. So astronauts in the International Space Station feel like that all the time. I suppose they must get used to it, so that it no longer feels terrifying.

Forgive the long diversion. There is a relevance to the topic, which is that a sudden disappearance of gravity would be obvious and traumatic, filling people with terror. So it would not be a good topic for contemplation of the unperceived.

I'm trying to think of an example. Perhaps this. Imagine the train is travelling across a bridge. All the windows are tightly shuttered so the occupants cannot see outside. The bridge is supported only at either end by bolts that can be simultaneously withdrawn at the press of a button. When the train is in the middle of the bridge, Lex Luthor presses the button and, without a sound (initially. After about a second the wind noise will become significant), the train, track and bridge goes into free fall, Under Einstein's principle of equivalence (crudely: acceleration is equivalent to gravity) gravity disappears for the occupants of the train.

Although there are no immediate visual or audible cues as to gravity's disappearance, the occupants will nevertheless be instantly filled with alarm, as they are suddenly struck by that stomach-in-throat, I just jumped off the diving platform, feeling. They will perceive the disappearance viscerally.

Fortunately, Superman turns up just in time and, supporting it from underneath, brings the bridge, track and train to a gradual, safe halt before transferring it to a nice stretch of flat land to let out the terrified passengers.

No humans were harmed in the conduction of this thought experiment.

I suggest you go and look up the meaning of the word 'if'.

The hiker didn't see the rock, but did any body else see it? If so, then the example is compatible with things only existing when perceived. If nobody saw the rock hit the hiker, not even the hiker (perhaps he was asleep), then how can anybody say with any degree of reliability that the rock actually did hit him? This hasn't been explained. — PossibleAaran

If you found a flattened hiker who had camped out next to rock face, then it's possible they didn't see or hear the falling rock. If it crushed them quickly enough, they may not have felt it either.

In that case, how could a non-existent rock do that? Or to put it into idealist terms:

How do we connect a rock we perceive to have crushed a human being with the cause of that human's death?

We can do it with realist language quite easily. But the idealist can't reference unperceived objects. We can't even reference the sleeping human here, because they might be unconsious, and without another perceiver, non-existent.

So you end up with the silliness that a non-existent rock crushed a non-existent human resulting in a perceived corpse and rock. That is, if things go out of existence when not perceived, and pop back into existence when perceived.

To go full subjective idealist mode, you just have a crushed corpse for no reason at all, where friends and family who identify the corpse with someone previously known will no longer experience interacting with that person as a living human. You get to avoid the stuff going in and out of existence, but then experience has these gaps to it and experiences happen without cause.

IOW, you ditch inference, and with it, explanations of any sort that aren't strictly deductive. You just have one experience following another for no rhyme or reason.

Does a fire continue to burn even when no one is looking? A critic of Stace had said that it must do so, because when you return to the fire after ten minutes, the wood has turned to ash, which is just what happens if you stay and watch the fire burn out. Stace pointed out that this argument assumes that the law of causation operates continuously through time, whether observed or unobserved, and this is obviously part of what needs to be proven. — PossibleAaran

Let's say you're shut in a vacuum sealed room with a fire. Both you and the fire are consuming the limited oxygen in the room.

Then a partition is put between you and the fire that blocks your from seeing, hearing or smelling the fire. It ceases to exist as a perception. Furthermore, there is a timer that will let you out before your run out of air, but only if the fire on the other side of the partition is no longer consuming air.

What happens? Do you survive or does your air run out? How would Stace answer that?

And there's many alternatives to this like introducing a poisonous gas you can't perceive or emptying the oxygen from the room, all setup to be automated with nobody else around.

And really, why would the question of needing air come up at all? Why would you die of needing something (oxygen) you can't perceive?

"I don't understand why this has to be the case. Isn't it conceivable that you exist just as you now do exist without the existence of a collection of atoms completely distinct from you? It might be true that scientifically speaking, to remove certain atoms from the world all together would cause a change in everything else (though I am not sure about this), but that presupposes the whole atomic theory and causation, and both of these presuppose that things exist when unperceived."

I like to picture reality as a slideshow. Each moment that passes then, I consider it to be one slide in an infinite amount of different ones. If you take one of these slides and examine it, you will be able to notice that it depicts every single thing that exists at a particular point in time. If you examine each one of the objects on this slide, you will also notice that each of them is defined by a particular limit that defines its shape. Now, let's say that among these objects there is a paper sheet. If you were to erase what is outside the limit that defines the paper sheet and left nothing but blackness around it, this blackness would still have a limit, for the existence of the limit that defines the paper sheet would necessarily define the boundaries of the blackness around it. Now then, if instead of erasing what is outside the limit that defines the paper sheet you erased what is actually inside it, you would notice that that which was not the paper sheet is still bounded by the limits of that which was the paper sheet. What I want you to notice is that even though you erased the paper sheet, you did not take it out of existence, for its limit seems to be, in reality, defined not by the paper sheet itself but by that which co-exists with it, and the same can be applied to every object on that or any other slide. Now, coming back to the paper sheet on the slide, I believe (all I have been saying is just a product of educated guesses, just to be clear) that in order to delete the limit that defines the paper sheet (that is, take it out of existence) you would necessarily have to alter the limit of the things that surround the paper sheet, for if you did not, the things that are not the paper sheet would still define the limit of the paper sheet itself.

I think a whole generation of philosophers, and an increasing number of those considering themselves scientists, would question in what way verifiable testing produces truths that are categorically more rigorous from truths detemined through other discourses, such as philosophical.

I think you should drop the dualistic logic and adopt some recent thinking from
perceptual psychology. The interesting question would be not whether some thing exists outside of a perception of it but what does it means in a pragmatic sense to be an object of a perception for a given person at a given time. . Let's take that piece of paper in front of you for instance. Let's see the myriad troubles we can get into by trying to maintain the assumption that the very idea of a piece of paper as a self-persisting 'thing' is coherent in the first place.
So we're talking perception here, and the implied modality is visual. I could of course be blind and then would have to determine the existence of the paper via another sense.
So I see the paper, right? But it's not that simple. What if I glance in the direction of the paper but don't process it as a piece of paper. We do that all the time. Our minds are preoccupied with other thoughts and we look right through something, not identifying it conceptually as 'this object'. And the act of identifying the paper as a thing is a protracted process. At first our visual system will process edges and then move on to a more encompassing recognition of the object. And our intentions and presuppositions enter into the perception in complex ways. Is why we're looking at the paper, in what context, really irrelevant to the meaning for us of what exactly the paper is?
Classical logic would say these are peripheral and irrelevant issues to defining the paper as physical entity, but classical logic is content tomsubstitute an impoverished abstraction for the more fundamental interactively determined meanings of how we interact with a world.
What is actually 'out there' and what our memory adds to what is out there interact inseparably. Now, if instead of a human perceiving thepaper, we take a snake, the perceptual mapping of the works will look quite different, since perception is about interacting with an environment adaptively in relation to one's needs, rather than representing, mirroring or copying something. The idea of object would be, to say the least , wry different for a snake, if in fact a sense of persisting thing was necessary at all for it.
We could demonstrate how different the perceptual mapping of a world would be if we used a human infant, also, one who had not yet established object permanency, and for whom a piece of paper would likely not exist as a coherent object yet.
So the upshot here is that, based on the current research understanding of perception as a a construction and an indissociable interaction between subject and object, what exactly would be appearing and disappearing in our world as our attentive processing shifted from moment to moment would not only be relative person to person, or creature to creature, or developmental stage to developmental stage, but also moment to moment.
It would seem that , in a real sense, the world of 'objects'as old fashioned metaphysical dualists define them in logical terms, never existed in the first place, and in fact the world of perceptually processed experience really does consists of particular meanings(objects of sense) that disappear as what they were the instant out attention wanders from them, and then have to be constantly reconstructed in relation to our purposes and intentional ends.

So, all the 'machinery' that we believe gives rise to perception, and that is never itself perceived during acts of perception, does not exist?

As to your suggestion that Kantian Idealism is about 'how we know what we know', the question depends on the word 'know' which is intolerably vague, and so it is hard to assess how Kantian Idealism is an answer to that question without an explication of 'know'. — PossibleAaran

I would think that Kant’s Critique of Pure Reason would be still considered amongst the most significant philosophical texts on that question. Not that Kant is the be-all and end-all but it does still provide an indispensable framework for discussion of this question in my opinion.

So, all the 'machinery' that we believe gives rise to perception, and that is never itself perceived during acts of perception, does not exist? — Janus

Apparently your eyes and brain don't exist when nobody's perceiving them, but you can still have a visual perception.

LOL, what absurdities some metaphysical standpoints commit adherents to! :s

LOL, what absurdities some metaphysical standpoints commit adherents to! :s — Janus

Indeed. There were huge disputes over some of these absurd commitments back on the old site.

Something just occurred to me. Can you classify a visual experience as a perception if your perceptual system doesn't exist since nobody's perceiving it?

I believe that there are items which exist when neither I nor anyone else is perceiving them. Examples of such items are pieces of paper, seas, mountains and apartment blocks. I believe it, but how could I possibly know it? — PossibleAaran

Well, mostly we take it on trust, on the word of others - friends, family, journalists - or of experts. That's a loose, everyday sense of knowing. Mostly we are confident about this mass of information, but we still retain some caution at the back of our minds, because doubt is always possible, and if we do doubt we can move on to the next stage.

If we're more curious, we'll look into the reasoning and arguments provided by our informants, and such demonstrations will ultimately boil down to there being some causal chain connecting present experience to the unperceived object, such that if the object didn't exist, our present experience wouldn't be the way it is. Or: the hypothesis that the unperceived object exists, is a reasonable explanation for present experience's being the way it is. (This would be so even if you're using your informants' experience as an intermediary step.) That would be your second type of knowledge - reliable inference. Doubt is still possible, but we have an overall picture that we can reasonably be confident in.

As to the general question, "How could we possibly know that things in general exist unperceived?" - that is self-evident if one is seriously using the term "we." (IOW, you're already admitting there's a "we" so you're already admitting that there are at least some objects outside of your present perception.) That's the first type of knowing, although here the demonstration is only possible by virtue of the logical implications of the terms used - or rather, by virtue of what's necessarily implicitly affirmed if the terms are being used seriously, non-frivolously. (There is no option for the question to be "free floating," spoken by no-one to nobody nowhere at no time - gradually take all that context away, and the question itself gradually becomes more and more meaningless.)

On the other hand, if I am asking the question of my own experience (methodological solipsism) - "How can I alone, out of my own resources, know that things exist unperceived?" - then there is no answer, and I am led inevitably to solipsism.

It would seem that , in a real sense, the world of 'objects'as old fashioned metaphysical dualists define them in logical terms, never existed in the first place, — Joshs

Old-fashioned i.e pre-Cartesian dualists didn’t think in terms of ‘objects’; that really came about because of Newton and Galileo. But I agree with the rest of your analysis which clearly comes out of phenomenology and therefore, ultimately, Kant.

Also we should remember Berkeley’s original aphorism was esse est percipe, to be is to be perceived. The word ‘exist’ doesn’t come into it.