how could everything be an illusion if?

Nihil est in intellectu quod non prius fuerit in sensu: (Lat.) Nothing is in the intellect which was not first in sense. All the materials, or content, of higher, intellectual cognition are derived from the activity of lower, sense cognition.

This is accepted by both Empiricists and Rationalists, who simply differ on how important continued experience is after a certain point. It was denied entirely by Socrates whose "Socratic method" was intended to prove that each of us is born with all knowledge; but Socrates did not deny the evidence of a physical world.

Kant (in the modern era) gave us this idea that what is in our minds is all that is available to us because we cannot know the "real reality" he called Noumena. But he did not deny the evidence of a physical world.

Denial of a physical world is not nearly as common as you make it sound. Few philosophers have gotten away with theories about nothingness that are plausible enough to warrant taking them seriously.

But hyper-skepticism, the idea that nothing exists until we can prove it exists, was the basis for Descarte's influence on epistemology, leading to Hume, who led to Kant. It is an epistemological construct called the prior certainty of consciousness, in which one presumes that only one's consciousness exists, and that the things we see in our minds must be proved to exist or not.

The obvious mistake is that a consciousness with nothing outside of it to make it aware of things is a contradiction.

It relates to the ancient subject-object problem, which can be defined this way:

"The epistemological predicament of a knowing mind which, confined to the circle of its own ideas, finds it difficult, if not impossible, to escape to a knowledge of an external world." see Ego-centric Predicament: http://www.ditext.com/runes/e.html

You are basing your argument on the flawed idea that your beliefs determine the nature of reality. You believe that you are interacting with therefore you determine that they are real. It is possible to physically interact with objects inside of a dream but that does not make them real. You are a partial being and your belief that the world you inhabit is real colors your perception of reality. Just because you experience something does not mean it is real. Hinduism teaches that this world is an illusion and that there is only Brahman. A small part of Brahman thinks it is you and takes part in the illusion but that does not make the illusion real. You do not exist, the chair does not exist, the world does not exist, there is only Brahman.

how could everything be an illusion if?

~~~ Everything is real!

Everything is true!

The notion of 'illusion' is no more than a vain thought. It is what one person calls the perceptions of another when it does not coincide with his perceptions. He, in ignorance, doesn't understand that all Perspectives are unique!

What is perceived, exists.

Not anything exists that is not perceived.

What exists is real.

Whatever is perceived is real.

As a vain 'thought/ego', is the only place that 'illusion' exists (as the 'thought' as which it is perceived).

"For every Perspective, there is an equal and opposite Perspective!" - The First Law of Soul Dynamics (Souls = Conscious Perspectives = us)

"The complete Universe can be defined/described as the sum-total of all Conscious Perspectives (us, Souls)!" - Book of Fudd

Every Perspective, no matter how 'unique' is a feature of Reality!

Reality is all inclusive!

'Materialism' is an refuted and obsolete philosophy. Learn some science!

What is illusion?

I see the tree as tall/short tree. I see the tree as beautiful/ugly tree.

Dualistic perceptions are illusions because they are relative and not absolute.

What is real?

I see the tree (not tall or short, not beautiful or ugly).

What is stupid illusion?

I see not a tree. I see atoms, molecules, etc....

Or, I see nothing (nihilism).

@ Nameless

You're contradicting yourself. In one of the question about whether a tree falling will make a sound. And you say that (in my own words) there's no sound outside the ear. And that there is no light outside the eye. Now you say

"What is perceived, exists. Not anything exists that is not perceived. What exists is real. Whatever is perceived is real."

That's contradictory.

assume that each and everything is phantasm and there is not any threat of ever understanding actuality. First, the incontrovertible fact that each and each element is illusory is a actuality unto itself. Logically, the single invalidates the different. 2d, if its authentic, how will it exchange the way you reside your existence. i in my view think of that phantasm is an thought and not a actuality. The absence of light skill darkness. I greater liable to settle for the thought its all delusion. the easy isn't absent yet its inadequate for seeing each and everything. the place the easy strikes, we see. the place it would not the dimness distorts our senses and we make incorrect assumptions approximately what we are watching. Its a sturdy question. an staggering undertaking for a koan. save asking and according to hazard somewhat easy could desire to attain the darker places.

An illusion is speculation (caused by lack of information), or a false idea caused by purposeful concealment of information. There are lot of things we don't have information about, so when it comes to these subjects we live in an illusion of our own making.

You see a man, he is stumbling. Is he drunk? Is he sick? Has he just remembered something that moved him to his knees?

Where's the information, living on the precipice of a question.

reality is present