I think the opposite: it begs the question how the world can continue to exist independently of the self (or selves) — RogueAI

What makes you think that? From what we can tell, the universe existed long before sentient life or "selves" came into existence. Why would things like stars, galaxies, elements, fire, radiation, and everything that makes up what we call the physical world be contingent upon organic sentient life?

If you are not a Platonist, mathematical objects may depend on or be nothing more than objects emerging from brain processes. And a physicalist will have to demonstrate that. The conclusion you reach is false. But my argument holds. If we are not Platonists we can say that truths depend on a world beyond the perception that guarantees their possibility. We can, if we are not Platonists, say that we are only talking about physical and chemical processes that occur in the brain and that a mathematical truth is based on these processes. — JuanZu

Mathematical (and other formal) truths have nothing to do with matter, energy, space, time, or Platonic entities. Yours is a false dichotomy.

"All As are Bs, all Bs are Cs, therefore all As are Cs" is a valid argument.

The above statement is objectively true and does not depend on the existence of an external world. Its truth has nothing to do with matter, energy, space, time, my brain, your brain, or a hidden realm of immaterial, magical entities that is somehow able to attach itself to our thought processes.

Do mathematical truths have nothing to do with matter and energy? I agree, that's why I'm not a physicalist.

If the example you have given is a truth, it is only a condition that its meaning is the same, for example, when another person says it; or even if both have already died and it is encrypted in a text. It is something that belongs to the essence of truth, to be valid beyond subjectivity and perception.

Thus, a truth, this time a truth about existence, our existence, if it is a truth, in order to be that, a truth, has the condition of not being reducible to perception and consciousness. If it is not reducible to this, this means that its nature reaches and is situated in the exteriority of the non-perceivable [World, texts, words, other people, etc.].

Those who doubt the existence of the world fall into an ontological version of the liar's paradox.

Do mathematical truths have nothing to do with matter and energy? I agree, that's why I'm not a physicalist. — JuanZu

Physicalism is a position regarding what sorts of things exist.

Your claim here suggests that you think that a statement can only be true if it "corresponds" to something that exists, and so that if a true statement is about something non-physical then it must correspond to some non-physical thing that exists.

This is a mistaken view. Not all truths depend on the existence of something.

Your claim here suggests that you think that a statement can only be true if it "corresponds" to something that exists, and so that if a true statement is about something non-physical then it must correspond to some non-physical thing that exists. — Michael

No. I claim that the essence of objective truths cannot be reduced to either perception or subjectivity. If there are truths it is of condition of this excess with respect to subjectivity. A truth can be about something physical, about mathematical, linguistic, sociological, economic objects, etc. But for it to be true it must exceed the order of perception and subjectivity. Even if it is a truth about subjectivity itself I.E “I perceive, therefore I am.”

I claim that the essence of objective truths cannot be reduced to either perception or subjectivity — JuanZu

You’re doing more than that: you’re claiming that objective truths depend on the existence of an external world, but this is false.

If only my mind exists then it is objectively true that nothing other than my mind exists (even I were to believe otherwise), and this objective truth cannot be reduced to either perception or subjectivity.

Objective truths do in fact depend on an external world, a world that I have defined as a non-perceptual exteriority beyond subjectivity that also encompasses subjectivity. And this includes truths about subjectivity. A statement like "It is true that only my subjectivity exists" is a contradictio in adjecto. And we deduce this from the conditions so that a statement, whatever it may be, can be true. And these conditions imply that a truth to be in effect a truth must exceed the subjective order, just as the truth exceeds the order of opinion [doxa], to take an example.

a world that I have defined as a non-perceptual exteriority beyond subjectivity that also encompasses subjectivity. — JuanZu

I have no idea what this means.

My use of the term is what I believe is most common.

But rather than split hairs over the meaning of “external world” I’ll be more specific with my claim:

Some objective truths (such as those of mathematics) do not depend on the mind-independent existence of matter, energy, space, time, or abstract objects.

How do conscious minds emerge from mindless unconscious stuff? Science hasn't answered it yet, and my belief is that science won't answer it because the idea that minds can come from mindless matter is nonsensical.

Since the appearance of subjectivity described as interiority separated from the world, we have called the external world as that which is not subjective, that is not a perception and that it is in its being to exist independently of perception, as an exteriority. I have deduced an external something, which also implies non-perception in its being, and also its being independent of perception, and also its exteriority, taking as a resource the question about objective truths..

Truth itself <is> purely conceptual. — PL Olcott

When I say that there is an object on the table and that the name of this object is "apple", these are facts. I'm telling the truth.

When I think about why is it called "apple", how to describe it, what is its nature, why apples exist, etc. I'm getting into concepts. These are not facts. They are subject to interpretation. So, we cannot call them "truth".

***

From Stanford Encyclopedia of Philosophy:
https://plato.stanford.edu/entries/facts/
Facts
"Facts, philosophers like to say, are opposed to theories and to values (cf. Rundle 1993) and are to be distinguished from things, in particular from complex objects, complexes and wholes, and from relations."

Concepts vs. Facts
https://teacherthompsonblog.wordpress.com/2016/01/24/concepts-vs-facts/
"A concept is an abstract idea generalized from particular evidence; a fact is something that is known to be true, or a thing that is indisputably the case. To compare, a concept is something that can be understood, and a fact is something that is usually memorized."

Teaching Facts, Skills, Concepts, and Morals: What’s the Difference?
https://people.ucsc.edu/~ktellez/facts-skills-con.html
"Teaching Facts
Teachers help students learn facts—that is, verifiable pieces of specific information. Facts take a variety of forms, including definitions, names, dates, and formulae."
"Teaching Concepts
Teachers are generally most concerned with conceptual learning because it helps learners to understand why. Concepts are distinguished from facts in that they are a much broader, deeper type of knowledge."

Concepts vs. Facts
https://sapeter.wordpress.com/2011/01/30/edu-6526-concepts-vs-facts/
"A concept is an abstract idea generalized from particular instances or evidence, so involves an inductive process or thought” (Sheuerman, R.). By contrast, a fact is something known to be true, it’s a piece of information. To oversimplify the difference, facts are memorized where as concepts are understood."

Concepts vs Facts
https://www.youtube.com/watch?v=XivCupQuIik
"Understanding the name of a bone is a fact. Understanding what it does in the body gets into a concept."
"You got to memorize bones, muscles, organs, tissues, a lot of it. But if you simply memorize and don't understand the
function of it the comprehension of the actual concepts it's a lot of wasted learning."

That the world exists (an abstract concept) is verified to be true (also an abstract concept) on the basis of anything that appears to be any physical sensation (not merely an abstract concept).
— PL Olcott

But what isn't verified is that there is more to the world than those physical sensations. — Michael

That is outside of the scope of the original question.
In one sense or another the world <is> proved to definitely exist.

When I think about why is it called "apple", how to describe it, what is its nature, why apples exist, etc. I'm getting into concepts. These are not facts. They are subject to interpretation. So, we cannot call them "truth". — Alkis Piskas

Whenever we are dealing with phonetic or symbolic encodings of semantic meanings we are dealing with abstractions. When we are looking directly at an apple the visual sensation of this apple is not an abstraction. The entirety of reality is sensations and abstractions.

The two theories of truth: correspondence deals with sensations and and coherence deals with abstractions. AKA the synthetic versus analytic divide.

Of course things we aren’t perceiving exist. The alternative is nonsense. The function of our sense organs is to perceive things that exist. How could I perceive something that doesn’t exist?

If a cup doesn't exist before I turn my head and look at it, why is it a cup that comes into existence? Who not a land shark? Or tomato? Or neutron star?

If something doesn't exist until I turn my head and see it, it seems a bizarre coincidence that the things that did not exist but come into existence happen to be perceptible with my eyes. Or are we suggesting many other things also come into existence that are not perceptible with any of my sense organs, and I only perceive those that happen to be perceptible with my sense organs?

Why do I need to turn my head for something that does not exist to come into existence? Why don’t things pop into existence in front of my eyes as I’m staring at a blank wall?

I doubt anyone has ever perceived a bullet that killed them. How is it they died if, not perceiving the bullet, it could not have existed?

If something that exists goes out of existence because I’m not perceiving it, then comes into existence again at a later date when I perceive it, why would it appear different, as though it existed throughoit that period of time?

All of these questions are easily answered if things exist whether I perceive them or not. They are not easily answered, particularly not all of them, if things do not exist when I do not perceive them, but do exist when I do perceive them. The laws of physics makes sense if things exist whether I perceive them or not. The laws of physics do not make sense if things do not exist when I do not perceive them, but do exist when I do perceive them.

Of course things we aren’t perceiving exist. — Patterner

I don't perceive Santa. Does he exist?

How could I perceive something that doesn’t exist? — Patterner

Dreams? Hallucinations? A VR headset?

Of course things we aren’t perceiving exist.
— Patterner

I don't perceive Santa. Does he exist? — Michael

No.

How could I perceive something that doesn’t exist?
— Patterner

Dreams? Hallucinations? A VR headset? — Michael

Yes, yes, of course We can come up with many different scenarios that are not the topic under discussion. I believe the topic is physical things in the real world.

I believe the topic is physical things in the real world. — Patterner

How do I know that I am perceiving a physical thing in a real world and not just dreaming or hallucinating or being tricked by an evil scientist who has my brain in a vat and is stimulating my visual cortex with nanomachines?

This question seems relevant to the discussion.

I believe the topic is physical things in the real world.
— Patterner

How do I know that I am perceiving a physical thing in a real world and not just dreaming or hallucinating or being tricked by an evil scientist who has my brain in a vat and is stimulating my visual cortex with nanomachines? — Michael

It is by definition impossible to detect the difference between reality and a perfect simulation of reality.
If the simulation is less than perfect then there may be tell-tale signs.
If (for example) reality is a projection from one's own mind, then one might see signs of this.

It is by definition impossible to detect the difference between reality and a perfect simulation of reality.
If the simulation is less than perfect then there may be tell-tale signs.
If (for example) reality is a projection from one's own mind, then one might see signs of this. — PL Olcott

Sure. But if one had only ever experienced a poor simulation of reality and never experienced reality then one wouldn't know that one was experiencing a poor simulation of reality and not experiencing reality.

Perhaps in reality grass is red and the Earth has two moons.

Is there a difference between reality, dreams, and hallucinations?

Is there a difference between reality, dreams, and hallucinations? — Patterner

The things we see when we dream and hallucinate are not mind-independent, and don't continue to exist when we don't see them, whereas (many believe) the things we see when we are awake and not hallucinating are mind-independent, and do continue to exist when we don't see them.

Sure. But if one had only ever experienced a poor simulation of reality and never experienced reality then one wouldn't know that one was experiencing a poor simulation of reality and not experiencing reality. — Michael

We can tell that it is not a poor simulation.
Detecting the subtle difference between a very excellent simulation and a perfect one might prove very difficult. If my understanding of Zen Buddhism is correct then this is the primary focus of Zen.

Is there a difference between reality, dreams, and hallucinations? — Patterner

Well, if here were not, why would we have three distinct terms for them?

And that pretty much sums up this thread: failure to pay attention to how words function.

Is there a difference between reality, dreams, and hallucinations?
— Patterner

The things we see when we dream and hallucinate are not mind-independent, and don't continue to exist when we don't see them, whereas (many believe) the things we see when we are awake and not hallucinating are mind-independent, and do continue to exist when we don't see them. — Michael

That seems reasonable to me. But you ask: "How do I know that I am perceiving a physical thing in a real world and not just dreaming or hallucinating..." If you don't know how to tell the difference, how do you know there IS a difference?

Regarding Demon/Matrix scenarios, my default position is that things are exactly as they seem. If anyone thinks my disembodied brain is wired up and being fed a simulation, I'd be interested in the evidence. I don't expect there is any.

Is there a difference between reality, dreams, and hallucinations?
— Patterner

Well, if here were not, why would we have three distinct terms for them?

And that pretty much sums up this thread: failure to pay attention to how words function. — Banno

Indeed. That is my point. If you know they are different things, why ask how you can know which you are experiencing? Which category does your experience fall into? There's your answer.

How do I know that I am perceiving a physical thing in a real world and not just dreaming or hallucinating or being tricked by an evil scientist who has my brain in a vat and is stimulating my visual cortex with nanomachines?

This question seems relevant to the discussion. — Michael

How do you know?

Don't you think that might be asking a little too much? It seems to me that Ockham's Razor suggests it's fairly reasonable to chop off the evil scientist as unparsimonious.

We can tell that it is not a poor simulation. — PL Olcott

How so? Maybe this is exactly what a poor simulation is like. Perhaps in reality grass is red and the Earth has two moons.

We can tell that it is not a poor simulation.
— PL Olcott

How so? Maybe this is exactly what a poor simulation is like. Perhaps in reality grass is red and the Earth has two moons. — Michael

If it was a poor simulation we would never be having this conversation because it would be common knowledge that everyone would know.

That seems reasonable to me. But you ask: "How do I know that I am perceiving a physical thing in a real world and not just dreaming or hallucinating..." If you don't know how to tell the difference, how do you know there IS a difference? — Patterner

I know that there's a qualitative difference between the experiences I consider dreams and the experiences I consider wakefulness. I presume that the things I experience when I dream are not of external world objects. I then wonder if perhaps that the things I experience when I'm awake are also not of external world objects. I then further wonder if there are external world objects at all.

If it was a poor simulation we would never be having this conversation because it would be common knowledge that everyone would know. — PL Olcott

I don't see how this follows.