Under that new (less than perfect) definition, a table is definitely physical, even if only an illusion. — Samuel Lacrampe

But I think what would be desired of anything that was truly physical, would be that it is real independently of any perception of it; its reality would not be dependent on it being perceived. Whereas, an illusion can only exist in the mind of an observer, as an illusion is, by definition, an artefact of perception.

While it is debatable that the table that I perceive is real or an illusion, the undeniable fact is that I perceive a table. — Samuel Lacrampe

There was a famous philosopher, by the name of Berkeley, who said that what we take to be external objects are really only ideas in the minds of observers. And it seems that at this point, you're on the verge of conceding that he might actually have been correct. And if you wanted an example of what you defined as 'an extreme spiritualist' in the history of Western philosophy, then Bishop Berkeley would be your man.

So, to be honest, I think your argument is in trouble.

First let me see if I understand your argument:

You're using the fact that we can imagine as proof of the physical world. According to you we can only imagine things or combinations of attributes of those things that exist in the physical world. You provide an illustrative analogy in the blind man who, having never experienced vision, cannot even imagine the concept of color.

So, what you're saying is:

1. It is not possible to imagine things that don't exist in the physical world
2. If the physical world did not exist then it is possible to imagine things that don't exist in the physical world (IOW: If it is not possible to imagine things that don't exist in the physical world then the physical world exists)
Therefore,
3. The physical world exists

My question is how do you know premise 1 is true? Yes, your analogy of the blind man is good but I have doubts about whether it conclusively proves its point.

1. ''It is not possible to imagine things that don't exist in the physical world'' needs to be restated to reflect the truth of the matter. An examination of the statement reveals that an implicit assumption, unwarranted, is being made in the statement viz. the physical world exists.

For me the correct truthful statement is ''it is not possible to imagine things that have not been perceived''. This is accurate as it deletes the unwarranted assumption ''the existence physical world''.

Now we can review your argument again:

1. It is not possible to imagine things that have not been perceived
2. If it is not possible to imagine things that have not been perceived then the physical world exists
Therefore,
3. The physical world exists

We can now see that 1 is true but 2 is dubious as there's a possibility that our perceptions could be mentally generated, having no real physical correlate.

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. — Samuel Lacrampe

I don't think that I have misunderstood. Even what you consider to be an undeniable fact - that you perceive a table - is debatable, if, for example, by that you mean something other than, say, a representation - or, even if you do mean something like a representation, it's nevertheless still arguable whether or not that is physical. Some people would argue that it is not. Some people contrast the mental with the physical, and take the position that they're mutually exclusive. Some people, in a sense, deny the physical altogether.

I suspect that you have perhaps misunderstood, since you do not seem to have taken my criticism on board, given statements such as, "As long as the thing that I perceive has a shape or colour, then it is physical".

To that kind of statement, I'll just say again that you can't really win an argument by definition like that. And if that's not what you're trying to do, then let's see how you can show that to be the case, if at all. The common sense hypothesis has already be criticised, so that can't just be assumed. You have a burden to support that position.

Even if the table is an illusion, then it is an illusion of a physical thing. — Samuel Lacrampe

What's your argument for that, then? And how does it deal with counterarguments, like the ones that I have mentioned?

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. — Samuel Lacrampe

Your conclusion probably wouldn't be disputed by those who are not physicalists or dualists, even if they did challenge your premise (the bit were you imply that shape, colour, and energy are physical), so I don't think that that really matters in comparison to your other claims.

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. — Samuel Lacrampe

Good luck with that. The physical has to do with physics, as most would accept. But some people are not physicalists or dualists, and do not consider what it is that we perceive with regards to things which seem to be assumed by you to be physical objects to be physical objects.

If you only mean that they relate to physics, which, according to Wikipedia, is the natural science that involves the study of matter and its motion and behavior through space and time, along with related concepts such as energy and force, then I doubt that you'll get much disagreement. Physics does not in itself entail physicalism or the physical side to dualism.

But I think what would be desired of anything that was truly physical, would be that it is real independently of any perception of it; its reality would not be dependent on it being perceived. — Wayfarer

As I understand it, our disagreement lies around the definition of the term "physical". Let's take a step back. Instead of using the term "physical", let's use the term "colour" in the argument, as so:
1. We cannot imagine things we have not perceived in the past.
2. We perceive colours.
3. Therefore colours exist. Not necessarily the ones I directly perceive right now, (because I could be dreaming right now), but these colours must have existed at least in the past in order to enable me to imagine them right now.
Do you agree with the new simplified argument?

We can now see that 1 is true but 2 is dubious as there's a possibility that our perceptions could be mentally generated, having no real physical correlate. — TheMadFool

There seems to be a logical fallacy in that statement: How can our perception of a thing be always mentally generated, since you agreed in premise 1 that it is not possible to imagine things that have not been perceived. Let's say I perceive a table. It could be that this table is mentally generated, because I perceived a similar table in the past. How can I explain the perception of the past? It could be that that too was mentally generated from a perception of another table before that, and so on ... But How did I get the very first perception? Logically, the first perception of a table must come from a real table, since we agree in premise 1 that it is not possible to imagine things that have not been perceived. Also, I would rectify the syllogism as so:
1. It is not possible to imagine things that have not yet been perceived.
2. We perceive physical things.
3. Therefore the physical things we perceive exist somewhere. Not necessarily the direct things we perceive, but similar things that would enable us to imagine these direct things we perceive.

It sounds like we will not agree on the definition of the term "physical". What if I simplify my original argument and use the term "colour"? It changes the conclusion a bit, but not really the intent of the argument. Here it is:
1. We cannot imagine things we have not experienced in the past.
2. We perceive colours.
3. Therefore colours exist. Not necessarily the ones I directly perceive right now, (because I could be dreaming right now), but these colours must have existed at least in the past in order to enable me to imagine them right now.
Any objections? If not, then the same argument can be used for shapes, smells, sounds and so on.

How can I explain the perception of the past? It could be that that too was mentally generated from a perception of another table before that, and so on ... But How did I get the very first perception? — Samuel Lacrampe

I see what you mean. Basically there are two things: perception and the thing being perceived. You seem to think that perception requires a thing that can be perceived and this, per your logic, is the physical world.

However, consider the brain-in-a-vat theory. Stimulating the right centers in the brain could produce all perception in the absence of a physical correlate. How do you solve this problem for your argument?

It sounds like we will not agree on the definition of the term "physical". — Samuel Lacrampe

We may well agree, but I have been raising possible objections.

What if I simplify my original argument and use the term "colour"? It changes the conclusion a bit, but not really the intent of the argument. Here it is:
1. We cannot imagine things we have not experienced in the past.
2. We perceive colours.
3. Therefore colours exist. Not necessarily the ones I directly perceive right now, (because I could be dreaming right now), but these colours must have existed at least in the past in order to enable me to imagine them right now.
Any objections? If not, then the same argument can be used for shapes, smells, sounds and so on. — Samuel Lacrampe

Lets assume that I accept that without any objections. So what?

This sounds right.

Why would you leave out logic, morality etc. from a physical world? Are you thinking that a physical world would have to be some kind of a dense lump of matter without parts? It seems fairly clear that the physical world has different parts, and thus logical relations between them, such as parthood. Likewise, as long as there social creatures in a physical world there are also relations between them which depend on their behaviour. So there is morality in a physical world.

Interesting. I never heard of that theory before. I think I can still refute it, as so: If I perceive a physical thing and my brain is in a vat, then it is possible that I have never encountered that thing in my life. However, that illusion of the physical thing still came from somewhere. In this case, it was created by the designer of the brain-in-a-vat experiment, right? Thus the question is brought back: how did the creator of the experiment come about the idea of the physical thing which I perceive?

I can generalize the problem this way: every effect requires an adequate cause. The effect of me perceiving a physical thing requires a cause. It could be caused by the designer of the brain-in-a-vat experiment. But then, that requires an adequate cause too. Eventually, I think it must come from the existence of the real physical thing (or something similar to it).

So we agree that such things as colours, shapes, smells and sounds exist in the real world. That was the point of my original argument. It refutes the belief that no such things exists, that these are all illusions.

I then categorized these things as physical things, because my understanding of a physical thing is whatever has a spatial, time, or energy component to it; or can be perceived by the senses (sight, smell, touch, hear, or taste). It looks like we disagree on the definition of the term "physical", but that's okay, because at this point, we are merely arguing about labels.

While it is debatable that the table that I perceive is real or an illusion, the undeniable fact is that I perceive a table. — Samuel Lacrampe

Why is this the "undeniable fact"? What if what we thought you were perceiving was a table, but what you really were perceiving was a desk? How can you say that it's undoubtable that what you perceive is a table when you could be perceiving something else, and incorrectly calling it a table?

Interesting. I never thought of the term "physical" being so general. If your definition of "physical" contains all of these concepts too, then what do you consider non-physical things, if any?

How can you say that it's undoubtable that what you perceive is a table when you could be perceiving something else, and incorrectly calling it a table — Metaphysician Undercover

If I perceive a table, then I perceive a table. If I perceive a desk, that I perceive a desk. Calling a desk a table does not change the perception (if I understand you correctly when you say "calling"). If I call a desk a table, then I am dishonest, but that does not change my perception of it.

What if you perceive something, and you call it a table, but you are really perceiving a desk, and you just called it by the wrong name by mistake.

Hmmm. You have a point there. It does look like there has to be something to feed the imagination/mind and that is what you're referring to as the physical world. Am I right?

Looks like I've to call in the big guns...

In the beginning there was nothing. And god said let there be light and then there was light...

The point being what if mind precedes the physical?

So we agree that such things as colours, shapes, smells and sounds exist in the real world. That was the point of my original argument. It refutes the belief that no such things exists, that these are all illusions. — Samuel Lacrampe

No, that wasn't the point of your original argument, since there is no mention at all of "physical" in this argument.

Colours, shapes, smells and sounds are not the problem. That they exist in the real world is not the problem. And someone who denies the physical isn't necessarily committed to the claim that these things are illusions. None of that is incompatible with the claim that these things are not physical.

I then categorized these things as physical things... — Samuel Lacrampe

And that's the problem.

It looks like we disagree on the definition of the term "physical", but that's okay, because at this point, we are merely arguing about labels. — Samuel Lacrampe

No, it's not okay. It means that you haven't refuted anything unless your definition is accepted, which it probably will not be by most people who deny the physical. Yet aren't these the people who your argument is directed at?

Who wouldn't accept that there are many "things" which can be perceived by the senses? That is a major part of any position in which empiricism has a major part, and that is likely to be true of the people whom your argument is directed. The problem is defining these things as physical. By acknowledging these things, they would not have conceded anything to you.

As for the part about there being a spatial, time, or energy component to these things, that will either be accepted whilst rejecting the claim that this is physical, or it will be rejected on the basis that "space", " time" and "energy" are subjective, not objective, and are just words or concepts. They are not in the object, they are in the subject. They are mental, not physical. You can claim that the mental is physical, but again, that would be rejected by many.

Are you conceding that you cannot refute idealism (as contrasted with physicalism and dualism) on its own terms?

We perceive that everything has a cause, and that it becomes reason for a subsequent event. We call the understanding of this cause and effect as logic. The universe is logic. You can see this more vividly in mathematics. And so logic is the only vehicle on which our effort to sustain our existence, and to manipulate the universe, within our sphere of influence, to achieve happiness, can ride.

The concept of spiritualism is presented to us as supernatural; magical. But if the whole creation obeys logic, then how can spiritualism, or anything else be beyond logic?

Now, let us see how we apply logic. A child figures life based on its previous experiences, and often comes up funny reasoning. At the age 16 -18, we used to feel that we have all the answers. Then, in a few years we start observing that life is not all black and white. We all have experiences, how a baffling situation becomes non existent, once we find the right answer; what used to matter so much becomes unimportant. We start seeing that our database of accumulated experiences is inadequate.

The discrepancy comes from the difference between brain and the total mind (we call it heart), of which brain is only a small part. Our desires, love hate, instincts, etc. reside in our total mind, not in our brain.

Relaxing the mind takes us beyond brain. This is where answers to baffling situations pop-up from. I feel that brain only knows parameters based on experiences of our life, but integrated mind knows them all. This is how the realities of our baffling problems evaporate; how griefs are dissolved.

To me, to think with the whole mind, in calm state, is spiritualism. It gives me depth in understanding of my self and of people around me. I achieve more tolerance, towards myself and others; I receive more love and respect. It reduces my frustrations, anger, anxiety, guilt and unhappiness. We can call this character building. I don't know whether the universe is real or an illusion. I don't know eventually where or how far my method will take me. But I don't care. When the journey is so beautiful, who cares about the destination?

or it will be rejected on the basis that "space", " time" and "energy" are subjective, not objective, and are just words or concepts. — Chief Owl Sapientia

While I agree with the points you say previously, I disagree with this one. For if space, time and energy are subjective, then they do not exist in themselves in the real world. But my argument refutes that, insofar as we perceive them. Just plug the terms in the syllogism.

unless your definition is accepted, which it probably will not be by most people who deny the physical. — Chief Owl Sapientia

That was my attempt at defining "physical". What is your (or the idealist's) definition then? Maybe we can resume the argument from there.

Are you conceding that you cannot refute idealism — Chief Owl Sapientia

Let's make sure we agree on the definition first. Idealism: system of thought in which the objects of knowledge are held to be in some way dependent on the activity of mind. Is that adequate?

You can be mistaken about the real thing you are perceiving, but how can you be mistaken about a perception? To use the specific example, how can you mistakenly call a desk a table if you are perceiving a desk? The only way I see how is because the person doesn't speak english very well and thus thought that a desk was called "table" in english. But this would be an error in language, not in perception.

Am I right? — TheMadFool

That is right.

The point being what if mind precedes the physical? — TheMadFool

You are correct too. Indeed, it appears the argument is refuted if there exists a being which can create (or imagine) something out of nothing, and then pass it on to us. Such a power is typically attributed to God. I think this is why Buddhism survives this argument, if I understand Buddhism correctly, as such: The physical world does not exist, but a God (pantheistic) exists which imagines it all.

Note: I know your quote was from the Christian Bible, not from a Buddhist book. But since Christianity (at least most branches of it) believe that the physical world is real, then the argument was never a threat to it.

While I agree with the points you say previously, I disagree with this one. For if space, time and energy are subjective, then they do not exist in themselves in the real world. But my argument refutes that, insofar as we perceive them. Just plug the terms in the syllogism. — Samuel Lacrampe

You'd be arguing against Kant, if I have understood him correctly, at least with regards to space and time. (The term "energy" wasn't even used in its modern sense until after Kant's death).

And your syllogism doesn't work for the reasons I've said. It will only work if you're preaching to the choir, but what would be the point of that? And anything other than that would just be begging the question. So it's a lose-lose situation for you, it seems.

That was my attempt at defining "physical". What is your (or the idealist's) definition then? Maybe we can resume the argument from there. — Samuel Lacrampe

I've already given one. The physical is that which relates to physics, which is the natural science that involves the study of matter and its motion and behaviour through space and time, along with related concepts such as energy and force. This could be analysed and be found to consist in observation, reason, concepts and so on, which can be defined as mental, so these things themselves would not be physical except insofar as they relate to a study of things called physics. And the statements of physicists wouldn't be interpreted in accordance with scientific realism, but would instead perhaps be seen as "just a narrative" with no necessary "real world", "external", "objective", "materialistic", "non-mental" implications.

Let's make sure we agree on the definition first. Idealism: system of thought in which the objects of knowledge are held to be in some way dependent on the activity of mind. Is that adequate? — Samuel Lacrampe

Sure, let's give that a go. I don't usually argue in defence of idealism, and am playing devil's advocate.

You can be mistaken about the real thing you are perceiving, but how can you be mistaken about a perception? To use the specific example, how can you mistakenly call a desk a table if you are perceiving a desk? The only way I see how is because the person doesn't speak english very well and thus thought that a desk was called "table" in english. But this would be an error in language, not in perception. — Samuel Lacrampe

Perceiving, and giving words to what is being perceived are tied together in an act of interpretation. So if I see something at a distance and perceive it as a table, and call it a table, but I walk closer and see that I should call it a desk, don't you think I was mistaken in my perception? If I hear a baby crying, then I find out that what I heard was a cat, was I not mistaken in my perception? The mistake is in the interpretation of what is going on, what is happening, and that is the act of perception. How is it that you think that this is not a mistaken perception?

What you say "you can be mistaken about the real thing you are perceiving" says nothing more than "you can be mistaken in your perception".

No. As you said, you first perceived it as a table. You were not "mistaken in your perception" because a table is what you perceived. Then you later perceived a desk. Again, you were not "mistaken in your perception" because a desk is what you perceived. Let's say the real thing was in fact a rock (that looked like a table from afar). Then both your perceptions were wrong in identifying the real thing, but you were not "mistaken in your perception", because even though we are not certain about the real thing that we perceive, we are certain about the perception itself. I think you are using the term "perception" incorrectly.

Another example: Let's say I perceive a purple unicorn. I am not certain if it is an illusion or reality (though likely an illusion). One thing is certain though: I am perceiving a purple unicorn, and not a green dog.

The physical is that which relates to physics, which is the natural science that involves the study of matter and its motion and behaviour through space and time, along with related concepts such as energy and force. — Sapientia

If I understand correctly, we at least agree that space is part of the physical. And we previously agreed that my syllogism works for things as colours and shapes. But how can we have colours and shapes without space? For us to perceive or even imagine colours and shapes, these must occupy an area (2D space). IE, shrink the area down to zero, and we can no longer perceive these colours and shapes. Thus space is an essential attribute of colours and shapes. Let's recap:
-Colours and shapes exist in the real world (as proven by the syllogism).
-Space is essential for the colours and shapes to exist, therefore space exists.
-Space is part of the physical world (if I understand your definition correctly), therefore the physical world exists, at least the portion of the physical that includes space.

Regarding Idealism: If we agreed that shapes and colours are things in themselves (as per the syllogism), then they exist independently of the activity of the mind. This does not refute the claim that some objects of knowledge are dependent on the mind, but it refutes the claim that all objects are.

No. As you said, you first perceived it as a table. You were not "mistaken in your perception" because a table is what you perceived. — Samuel Lacrampe

How is this not a mistaken perception? When I perceive a table, then I later realize that what I perceived is really a desk, that is called a mistaken perception. I have bad eye sight, and quite frequently have such mistaken perceptions. I might see someone in a crowd, and think it's person X, only to find out soon, that it is not. How is this not a mistaken perception?

Again, you were not "mistaken in your perception" because a desk is what you perceived. Let's say the real thing was in fact a rock (that looked like a table from afar). Then both your perceptions were wrong in identifying the real thing, but you were not "mistaken in your perception", because even though we are not certain about the real thing that we perceive, we are certain about the perception itself. I think you are using the term "perception" incorrectly. — Samuel Lacrampe

I really don't understand what you are trying to say. You seem to be trying to give some odd definition to "certainty". I know I have bad eye sight, so I am never certain concerning my perceptions of distant things, I am always doubtful. You seem to think that you are always automatically "certain" concerning your perceptions, but I don't think that this is possible. To be certain requires conscious effort, justification, reasons to convince yourself of your certitude. If something just comes to you in a perception, you cannot be certain of that, until what you think, concerning your perception, has been justified. This is more evident with sounds. It's very often that we hear sounds, and are not certain of what the sound is. You have to go over in your mind, the sound, in your memory, to determine what it is. Hearing sound is just hearing sound, there is no reason to think that there is certainty involved in this. But if the sound is understood as something particular, this could be mistaken.

As a compromise, let's assume that there is such a thing as perceiving, seeing for example, without recognizing, or in any way associating what has been perceived, with something in memory, because this is where there could be a mistake. What would this simple act of perceiving, or seeing consist of? It surely could not consist of any form of certainty.

Another example: Let's say I perceive a purple unicorn. I am not certain if it is an illusion or reality (though likely an illusion). One thing is certain though: I am perceiving a purple unicorn, and not a green dog. — Samuel Lacrampe

Don't you see this as nonsense? You are claiming that you could be perceiving a purple unicorn, and you are not sure whether you are really perceiving a purple unicorn or not, yet you are certain that you are perceiving a purple unicorn. You just contradict yourself. You respect the fact that your perception might be an illusion, and therefore mistaken, yet at the same time you claim to be certain of your perception.

So we still disagree because for you, the statements "mistaken about the real thing perceived" and "mistaken about the perception" are the same thing, and for me, they are not. Let me try to explain why in another way:

Let's say I feel sick. I go to the doctor and, upon testing everything (let's say we are able to test everything), it reveals that I am not really sick. Thus the feeling was not reflective of reality, but at the time that I felt sick, I felt sick. I was not dishonest with the doctor, because the feeling itself was real, even though the sickness was not. This is an example of being mistaken about the real thing perceived (the presence of real sickness) while not being mistaken about the perception (the feeling of sickness).

I think you are just creating a fictitious, impossible scenario, for your example. You are saying, suppose I feel sick, and there is absolutely no reason why I feel sick. Do I really feel sick or not? I believe that if you feel sick, there is necessarily a reason why you feel sick, so the premise of your example, that you feel sick, and there is no reason for this, is an impossibility.

Therefore, I still think that your separation between being mistaken about the real thing perceived, and mistaken about the perception itself, is false. You only support it by referring to an impossibility.

Alright, assuming that you are correct, it only shows that my example is not a good one, but this falls outside of my main point. My main point is simply to make you understand what I mean when I say "we cannot be mistaken about our perceptions" which is not what you think it means. Let's try again.

When we observe the stars from the earth, we observe that they twinkle. In reality, stars don't twinkle and it is an atmospheric effect. Let's say I am a teacher asking a student what he sees when looking at the stars. He should say "I observe that they twinkle". He will be correct because that is indeed what he should see when looking at the stars. Not drawing any conclusions about the real things observed, he is "not mistaken about his perceptions". That is all that I mean by this. We might disagree on the label, but you just need to understand what I mean behind the label I use.