Are you assuming that the world would be made of your perceptions or imaginations? Why else would you claim that the question whether the world is physical would depend on our ability to perceive physical things? — jkop

My argument is not from cause to effect, but tracing the effect back to the cause. The effect of our perception of the physical world requires an adequate cause. That cause must be a real physical world. Could it be something else?

The effect of our perception of the physical world requires an adequate cause. That cause must be a real physical world. Could it be something else? — Samuel Lacrampe

Here you're just assuming, or begging the question that what we perceive with our sense IS a physical world, which the idealist disputes. The idealist also disputes that his experiences require "an adequate cause" - which is the exact same thing that you are doing, except in regards to the physical world. You hold that the physical world is a 'cause', and isn't an effect of something else/some other level of reality.

The difference between the two positions is which level of reality is uncaused/requires no 'adequate cause'. So demanding the idealist explain what's causing everything experiential to exist is missing the point - the idealist holds that experiential things are uncaused - there *isnt* some other level of reality (such as a physical world) causing them to exist.

Why do you not in return though, need to explain where the physical world comes from? — dukkha

I think your concern misses the mark. If only a spiritual world exists, even if it is uncaused, then we could never perceive a physical world, due the limitation of our imagination, as explained previously. But we do perceive a physical world. If a physical world exists, even if it is uncaused, then it explains the phenomenon of our perception. Now you demand a cause for the existence of the physical world. That is indeed left unanswered, but it stands outside of the original topic of discussion, which was to explain how it is that we perceive a physical world.

You can't jump straight into how it is that we perceive a physical world without first establishing that we perceive a physical world. Otherwise you'll be begging the question.

As for you argument, that can easily be countered. Just as you reason that things like "blue" are physical, and thus lead to a physical world, I can reason that things like "blue" are perceptual, and thus lead to an ideal (or "spiritual") world.

And as for cause and effect, that can also be rejected, in a sense, insofar as it relates to reason, as per Hume. You've said that there must be a cause, yet there is no necessary connection between the one and the other. Or, if there is, can you demonstrate this?

tracing the effect back to the cause. — Samuel Lacrampe

There are other things to perceive than physical objects, such as socially constructed objects, which are not so physical, nor are they imagined; they're agreements perceived as things to live by. From the fact that you perceive something it does not follow that the world is physical (unless you'd assume that perception must be the cause of a physical world, but then your argument would be circular and invalid).

'Spiritualism' is a rather old-fashioned term, used to refer to the Victorian belief in spirits, seances, spirit mediums, and the like. It ought to be differentiated from idealist philosophy (for instance) as it is possible to hold an idealist philosophical attitude, without adhering to belief in 'the spirit world'.

As regards the reality of 'physical things', it is feasible to argue that the world is a consistent illusion. That doesn't necessarily imply the reality of spiritual things, but it does undermine the view that everything can be explained in purely physical terms, or that what is physical is intrinsically or inherently real.

And indeed, there is a lot of uncertainty about what 'purely physical' might mean. Back in the day of spiritual seers and seances, it might have been believed that 'physical things' would be explained in terms of measurable entities and forces, such as atoms and electromagnetic fields. However, subsequently, the nature of matter has turned out not to be at all straightforward. Sober scientists nowadays are quite prepared to entertain notions such as 'many worlds' and the like.

As regards 'how we perceive the physical world' - seeing, perception, judgement and so on, are built around cognitive faculties. The question of how or if our cognitive faculties decieve us, or not, is one of the fundamental questions of philosophy. Sceptics nowadays are generally those who maintain that science provides the only arbiter of what ought to be considered real, but originally scepticism called into question the whole domain of sensory experience, on similar grounds to the above - that experience itself might be illusory. That doesn't necessarily mean the sceptics were correct but at least it's worth considering what scepticism originally means, in this context.

It's a very common metaphor, so I would be very surprised if you were not already aware of its meaning. It's used in that way to mean "to imagine or visualise". To see with your mind's eye. It's not meant to be taken literally, hence the scare quotes. — Sapientia

Oh really. But 'to imagine' is what I said, recall. The fact that "seeing" is a metaphor does not make its use appropriate, nor innocent, in a context where one argues for a rejection of its literal meaning in talk of imagination.

You can't jump straight into how it is that we perceive a physical world without first establishing that we perceive a physical world. — Sapientia

Well, I perceive a table in front of me. This table is a physical object, even if that object is only imaginary.

things like "blue" are perceptual, and thus lead to an ideal (or "spiritual") world. — Sapientia

I am not sure I understand this. Can you present the argument?

You've said that there must be a cause, yet there is no necessary connection between the one and the other. Or, if there is, can you demonstrate this? — Sapientia

Sure. Indeed, the existence of a physical world is not a necessary cause to the effect of my perception of physical things; but it is an adequate cause, thus a candidate. To refute this candidate, we would need to find other adequate causes to take its place. I can think of only one, which is God. Since God (should He exist) can create things from nothing, then He could create the idea of physical things in our minds without physical things existing in the real world.

I would describe the colour indirectly, by referring to its effects on people who can see it, by how they use the word 'red', describe things in which the colour occurs in nature, and its metaphorical uses etc. To imagine what it's like to see red is not to see anything, recall. Imagination is the evocation of an experience via knowledge of one's past or other experiences. Without any past visual experiences the blind can still use knowledge of other experiences, or knowledge of other people's visual experiences, in order to imagine what it's like to see red. — jkop

I don't see how that would work at all. Saying that green is the colour of grass and apples, that red is the colour of strawberries and apples, that cars come in many different colours, and that purple is the colour we associate with royalty and wealth, unless you're in Brazil or Thailand where it's the colour of mourning, won't help a blind person understand what it's like to see colours. How can you think it would?

Well, I perceive a table in front of me. This table is a physical object, even if that object is only imaginary. — Samuel Lacrampe

This is becoming rather tiresome. I'm interested in explanation, not just bald assertion.

I am not sure I understand this. Can you present the argument? — Samuel Lacrampe

Can you? I was just using analogous reasoning to your own in order to highlight the problem with it. If you have a problem with my argument, then you have a problem with your own.

I perceive a table in front of me. This table has not been demonstrated by you to be a physical object, whether that object is only imaginary or otherwise.

Sure. Indeed, the existence of a physical world is not a necessary cause to the effect of my perception of physical things; but it is an adequate cause, thus a candidate. To refute this candidate, we would need to find other adequate causes to take its place. I can think of only one, which is God. Since God (should He exist) can create things from nothing, then He could create the idea of physical things in our minds without physical things existing in the real world. — Samuel Lacrampe

By what method are you assessing whether or not a candidate is adequate? Explanatory power? If explanatory power were the only criterion, then perhaps. But I don't think that you've adequately explained this candidate. Induction? How then do you resolve the problem of induction?

I don't see how that would work at all. Saying that green is the colour of grass and apples, that red is the colour of strawberries and apples, that cars come in many different colours, and that purple is the colour we associate with royalty and wealth, unless you're in Brazil or Thailand where it's the colour of mourning, won't help a blind person understand what it's like to see colours. How can you think it would? — Michael

Perhaps he is blind, and has convinced himself that he knows what colour is like just like the rest of us. Or perhaps he is a pedant who has missed the point. He seems rather hung up on this issue, which isn't really even an issue in my view. I don't think that anyone here really meant what he's criticising. I see this as an unhelpful digression, although I myself have contributed towards it. (Oops).

I came up with an argument against extreme spiritualism, and would like your thought on the strength of it. Extreme spiritualism: the belief that the physical world does not exist, that all that exists is spiritual, and that the physical world is therefore all imagined. — Samuel Lacrampe

If we regard the physical world as the 'cause' of our phenomenal experiences, then the existence of the physical world - thus defined - is an assumption, based abductively (and hence partly subjectively) on our experiences. Immanuel Kant believed in a such a physical world, but argued that its constituents were imperceptible and unknowable - and also, one would imagine, unimaginable. He called them 'noumena'. He went to great lengths in his second version of the Critique of Pure Reason to argue that this did not make him an Idealist (which seems to correspond to what you are calling a 'Spiritualist'), although he would agree to being a 'Transcendental Idealist', a term he made up to describe his position.

I agree with Kant that he was not an Idealist (in the sense typically applied to George Berkeley, although Berkeley called himself an Immaterialist). He believed in the existence of a physical world. He just also believed that it was unknowable.

. . . ..won't help a blind person understand what it's like to see colours. How can you think it would? — Michael

Knowing that red is used in different ways in different cultures helps us understand what it's like to see red in different contexts. I think you ascribe the blind too many disabilities. A bind person lacks the ability to see; not to understand, nor imagine, what it's like to see.

I've never seen neutrinos, I can't see them, but I know a little about them: for example, that they are difficult to detect, even with sensitive instruments. That alone is enough for me to be able to imagine what it's like to detect them, or see them with my imagined super-naturally sensitive eyes.

Imagination is, unlike perception, an evoked experience which is closely related to perceptual experience but occurs under very different conditions. Instead of direct causal links and interaction with present objects there is knowledge, empathy, and the ability to evoke experiences we call imagination. Do you think that's controversial or false?

A bind person lacks the ability to see; not to understand, nor imagine, what it's like to see. — jkop

I would say they do (unless they were once sighted and have since lost their sight). We once had a blind poster on the old forum who asked us to explain sight to her and she couldn't make heads or tails of it, which is expected.

That alone is enough for me to be able to imagine what it's like to detect them, or see them with my imagined super-naturally sensitive eyes.

And when you imagine seeing neutrinos with your super-naturally sensitive eyes, what do you imagine? A tiny little ball, perhaps? I'm no scientist, but I'm pretty sure that would be completely wrong.

But even if it is like a tiny little ball, this analogy fails as you already know what tiny little balls look like. So for this comparison to hold, the blind person must have had some experience that is something like colours for them to understand colours, which they don't.

Imagination is, unlike perception, an evoked experience which is closely related to perceptual experience but occurs under very different conditions. Instead of direct causal links and interaction with present objects there is knowledge, empathy, and the ability to evoke experiences we call imagination. Do you think that's controversial or false?

I think it's controversial and false. How can the blind evoke an experience of a kind they've never had? Not only are the areas of the brain that are responsible for the experience of colour underdeveloped in the blind (and the areas of the brain that are responsible for the experience of colour are also responsible for the imagining of colour), but their brains haven't had the means to connect these areas to the areas that are responsible for imagining things that they do understand, which is why simply telling them that apples are green (or red) won't help them understand what it's like to see something that's green (or red).

I think you have a fundamental misunderstanding here.

---

There's an interesting article on blindness by Oliver Sacks called The Mind's Eye. In it he even describes how someone who was once sighted but lost his sight (due to an issue with his eyes, not with his brain) can't even imagine visual things any more (although others who lost their sight could remember - but I think it reasonable to suggest that those who've never experienced sight at all would be like the one who can't remember, given that the information was never in the brain to begin with).

There's an interesting article on blindness by Oliver Sacks called The Mind's Eye. In it he even describes how someone who was once sighted but lost his sight (due to an issue with his eyes, not with his brain) can't even imagine visual things any more — Michael

Interesting. I wonder how widespread this phenomenon is among the non-congenitally blind. In cases in which this "imagination blindness" occurs, perhaps it's because the visual cortex is being co-opted by something else (assuming that the visual cortex is even involved in imagining sight to begin with).

Interesting. I wonder how widespread this phenomenon is among the non-congenitally blind. In cases in which this "imagination blindness" occurs, perhaps it's because the visual cortex is being co-opted by something else (assuming that the visual cortex is even involved in imagining sight to begin with). — Arkady

I seem to recall reading somewhere yesterday about someone who was blinded later in life and then recovered their sight and after recovery realised that they had completely forgotten a lot of colours and had trouble distinguishing them.

Also, regarding your last consideration, there's this:

It was found that the imagined patterns and seen patterns produced similar waveforms, supporting evidence for the claim that the visual cortex is activated in a similar manner during both imagination and perception.

If we regard the physical world as the 'cause' of our phenomenal experiences, then the existence of the physical world - thus defined - is an assumption, based abductively (and hence partly subjectively) on our experiences. — andrewk

Yes, exactly. It is a retroductive hypothesis that provides a very plausible explanation for our experiences, which we can then deductively explicate and inductively evaluate by means of our subsequent experiences. However, we cannot know with absolute certainty that our experiences really do correspond to a physical world; just that they correspond to some kind of external world that reacts with us by resisting our actions and our wills, which is what "existence" means.

I agree with Kant that he was not an Idealist (in the sense typically applied to George Berkeley, although Berkeley called himself an Immaterialist). — andrewk

Peirce was intimately familiar with Kant's writings, but eventually chose to call himself an objective idealist instead. He understood "the physical law as derived and special, the psychical law alone as primordial," and stated, "The one intelligible theory of the universe is objective idealism, that matter is effete mind, inveterate habits becoming physical laws." In other words, he held "matter to be mere specialized and partially deadened mind," and that "matter is merely mind deadened by the development of habit," such that "dead matter would be merely the final result of the complete induration of habit reducing the free play of feeling and the brute irrationality of effort to complete death."

He believed in the existence of a physical world. He just also believed that it was unknowable. — andrewk

By contrast, Peirce believed that the physical world is knowable, precisely because matter and mind differ merely in degree, rather than kind. In fact, Peirce insisted that it was absurd to call anything "real" that was unknowable; the real is precisely that which would be known by an infinite community of investigators after an indefinite process of inquiry.

But we do perceive a physical world. — Samuel Lacrampe

Begs the question.

I perceive a table in front of me. This table has not been demonstrated by you to be a physical object, whether that object is only imaginary or otherwise. — Sapientia

As previously stated, I defined "physical" as: matter and energy. I would now add "anything that is perceived by the senses" for further clarity. Now a table is made of matter (atoms). Thus the table I perceive is physical.

things like "blue" are perceptual, and thus lead to an ideal (or "spiritual") world. — Sapientia

But the definition of perceptual is "involving perception especially in relation to sensory experience", and "sensory" is related to physical things. Thus according to that definition, this would make the perception of "blue" lead to acknowledging a physical world, not idealism, would it not?

By what method are you assessing whether or not a candidate is adequate? — Sapientia

To say that "the existence of X is an adequate cause for my perception of X" is really the common sense hypothesis and is therefore the default position. If you were to object to this, you would have the onus of proof to refute the claim, not me.

From the fact that you perceive something it does not follow that the world is physical — jkop

I guess not always. But how about perceiving things directly through the senses (seeing, hearing, smelling, touching, ...)? Aren't things that are perceived through the senses necessarily physical?

Begs the question. — dukkha

I defined "physical" as matter and energy. I perceive a table. The table is made of matter, thus is physical. Therefore I perceive a physical world.

The table is made of matter — Samuel Lacrampe

Again, you're just begging the question of the nature of things in the world. An idealist would dispute that the table is made of matter.

An idealist can just make the same begging the question argument: "I perceive a table. The table is made of my visual experience of it, thus is experiential. Therefore I perceive an experiential world."

. . .We once had a blind poster on the old forum who asked us to explain sight to her and she couldn't make heads or tails of it, which is expected. — Michael

Strange, because usually obscurity inspires people to imagine more, not less. Fiction thrives on it even.

And when you imagine seeing neutrinos with your super-naturally sensitive eyes, what do you imagine? A tiny little ball, perhaps? I'm no scientist, but I'm pretty sure that would be completely wrong. — Michael

Can imaginations be wrong? What is an example of a right imagination of something, anything?

. . .the blind person must have had some experience that is something like colours for them to understand colours, which they don't. — Michael

Here you're talking about understanding colours, not imagining them. And why would anyone need some experience that is something like colours to understand colours?

One counter argument might be that we can imagine, i.e. experience, fictional things we simply couldn't have had previous, nor similar, experiences of. Unseen colours even. Heard of blind painters?

How can the blind evoke an experience of a kind they've never had? — Michael

The question is incoherent, because one could not have something of a kind that one has never had.

From the lack of visual experiences it does not follow that the blind would therefore be incapable of imagining what it's like to have them. To imagine is to experience something real or unreal via knowledge, empathy, speculation, abductive reasoning etc.. We may imagine things impossible to perceive, or places impossible to visit and so on.

I think it reasonable to suggest that those who've never experienced sight at all would be like the one who can't remember, given that the information was never in the brain to begin with). — Michael

That's trivially true. But to imagine something new is not to remember something old. What do you know about imagination?


(EDITED for clarity, Feb. 22nd)

An idealist would dispute that the table is made of matter. — dukkha

But science claims that tables are made of matter. Surely I can appeal to the authority of science on this. At the very least, the scientific claims become the default position, and so the idealist disputing the claim agreed upon by science would have the onus of proof, not me.

Now a table is made of matter (atoms). — Samuel Lacrampe

Science can't really tell you if the world is real or not. It's feasible that the world might be a grand illusion, but an illusion that works consistently, in such a way that it is scientifically predictable. I don't personally subscribe to such a view, but the point is, that is a metaphysical question, rather than a scientific question - in other words, you can't appeal to science to resolve the question.

Secondly, the 'nature of matter' is really rather mysterious in its own right. It used to be thought that matter was ultimately composed of atoms, in the form of indivisible point-particles, but the nature of atoms has turned out to be quite deep question in its own right. That very question is the subject of the Large Hadron Collider, which is the most expensive and powerful scientific apparatus ever made. But at this point in time, there is still no truly 'fundamental particle' that has been found by the LHC.

Aren't things that are perceived through the senses necessarily physical? — Samuel Lacrampe

Investigate what it means for something to be physical, does it leave anything out?

As previously stated, I defined "physical" as: matter and energy. I would now add "anything that is perceived by the senses" for further clarity. — Samuel Lacrampe

You can't really win an argument by definition like that, because it isn't really a win. It's trivial, and anyone can do it. An idealist could do the exact same thing.

Now a table is made of matter (atoms). — Samuel Lacrampe

But that could be a controversial premise in the context of this debate, so it can't just be taken as self-evident. Its meaning and logical implications would have to be examined, as well as how you supposedly know this to be the case.

One could form a possible counterargument based on idealism, representationalism or scientific anti-realism, by claiming that "table", "matter" and "atoms" are just ideas, perceptions or concepts, or by claiming that we do not directly perceive any table or matter or atoms, but only representations, and that you therefore do not know what you claim.

But the definition of perceptual is "involving perception especially in relation to sensory experience", and "sensory" is related to physical things. — Samuel Lacrampe

The former is not inconsistent with what I said. One can use the adjective "perceptual" to describe it, and one could give it a name like "impression" or "sense-data".

The latter is begging the question again.

Thus, according to that definition, this would make the perception of "blue" lead to acknowledging a physical world, not idealism, would it not? — Samuel Lacrampe

If you define "sensory" in such a way as to do so, then yes, but that would be trivial and would miss the point. Obviously, that definition would simply be rejected, and not without good reason. This debate has been ongoing for a long time. It can't be settled that easily.

To say that "the existence of X is an adequate cause for my perception of X" is really the common sense hypothesis and is therefore the default position. If you were to object to this, you would have the onus of proof to refute the claim, not me. — Samuel Lacrampe

You could just read an An Enquiry Concerning Human Understanding by David Hume. He is quite critical of common sense.

Science can't really tell you if the world is real or not. — Wayfarer

I agree with this, but I think there is still a misunderstanding on the term "physical". Let me try to define it another way: A thing is physical if it has spatial attributes such as length, height, volume, etc. It is also physical if it has attributes related to energy, such as speed, force, noise emission etc. Finally, it is physical if it can be detected (by instruments) and measured. Under that new (less than perfect) definition, a table is definitely physical, even if only an illusion. My whole argument is not prove that the table that I perceive is real, but that if the perception of physical things exist, then there must exist a physical world somewhere.

Investigate what it means for something to be physical, does it leave anything out? — jkop

Yes. Concepts such as logic, morality, and justice are not perceived through the senses, and yet are undeniably real (at least logic for most people). They are therefore non-physical things. I would also add spiritual things like souls, angels and God, but these concepts can be controversial and so we can leave them out. If you disagree, what would you consider physical things versus non-physical?

I still think there is a misunderstanding. While it is debatable that the table that I perceive is real or an illusion, the undeniable fact is that I perceive a table. As long as the thing that I perceive has a shape or colour, then it is physical. Even if the table is an illusion, then it is an illusion of a physical thing. In contrast, non-physical things would be concepts such as logic, morality and justice, because they don't have physical attributes such as shape, colour, or energy. If these are illusions, then they would be illusions of non-physical things.

So the only obstacle I see to a mutual understanding is to agree on the definition of a thing being "physical". Once clarified, then the original argument is easily understood.