Descartes: I Think Therefore I Am

[jduster]

Descartes: "I Think Therefore I Am"

In following the rules, I will explain in detail what exactly is up for debate here, so this thread will not be locked.

"I Think Therefore I Am", a common phrase (maybe the most common phrase), was written by Rene Descartes in the 1600's in his book Meditations II. In Meditations I, he "demolished" the certainty of anything existing. His reasoning was that there is no way to prove that his thoughts are deluded or being deceived, as humans have been wrong. Some of the examples he provided was you could not disprove that there is an evil supernatural being tricking the human mind or simple everyday optical illusions that trick the mind. The next day in Meditations II, he wrote that there is one thing that he could be completely certain of, that he existed. His logic was that doubts of certainty were because of deluded thoughts. If there are thoughts to delude, thoughts exist, and "I" (in this case, Descartes) is a thinking being that exists.

Question: Does this common phrase which is often seen as self-evident provide solid proof to remove the doubt of "I" (in your case, yourself) existing.

---

My personal opinion:

Essentially descartes’ proof is:
X is true. Y is true. Therefore, X is true.

His argument is circular. "I think therefore I am" could also be "I am therefore I think".

It’s the same thing as to say unicorns are pink, therefore unicorns surely exist. How could something be pink if it doesn’t exist. It’s tautological. It’s the equivalent of saying apples are red and they are delicious, therefore apples are surely red.

You can replace the word think with ANYTHING. I eat therefore I exist. I dream therefore I exist. I walk therefore I exist. There’s no difference of what you say.

Philosophy is a part of linguistics. We use words, as our only means, to try to prove our ideas to other people. There is so many limitations to language. We may exist, but we are unable to use words to prove it.

Your thoughts?

 

[Ryan_m_b]

I think you went wrong with the "X is true. Y is true. Therefore..."

What "I think therefore I am" means is that whilst any sensory input and feeling can be faked you can't fake the feeling of existence because the being would have to exist for you to do that. I.e. you can convince a conscious being that they are not conscious but you cannot convince a non conscious entity that it is a conscious being.

 

[jduster]

I think you went wrong with the "X is true. Y is true. Therefore..."

What "I think therefore I am" means is that whilst any sensory input and feeling can be faked you can't fake the feeling of existence because the being would have to exist for you to do that. I.e. you can convince a conscious being that they are not conscious but you cannot convince a non conscious entity that it is a conscious being.

That is Descartes logic. And that applies to Descartes argument for skepticism. That does not necessarily apply to other arguments for skepticism, such as Hume's.

 

[Ryan_m_b]

That is Descartes logic. And that applies to Descartes argument for skepticism. That does not necessarily apply to other arguments for skepticism, such as Hume's.

I'm not sure how that applies to what I said. I was responding specifically to comments like this:

You can replace the word think with ANYTHING. I eat therefore I exist. I dream therefore I exist. I walk therefore I exist. There’s no difference of what you say.

Your mistake was jumping to apply the I think therefore I am logic to other things. It literally only works for thinking/existence/consciousness.

 

[wuliheron]

If it works for anything its because Descartes did not provide a rigorous definition for "I" and, as Ryan points out, it has to do with the "feeling" of existence. Its a nice compelling argument, but so is the idea the Earth is flat and like the idea the Earth is flat there exists endless evidence to the contrary.

 

[Thevic]

Well, to start a linguistics debate on Descartes is to beg for a ginormous discussion on everything from Nietzsche to Wittgenstein.

However, like someone else pointed out, Descartes was merely indicating that the "feeling" of thought is proof that he exists. Everything else: the world, his body, could be an illusion, but if thoughts are the basis of a human mind, then the fact that he thinks is the proof that his mind exists. Which is what he means with "I am".

Now, of course the language can't quite describe the "feeling of awareness". Nietzsche, for example, pointed out that nothing in the language accurately describes something else. He used to say that the language is full of metonymys and metaphors that aren't actually "the thing in itself", to use a Kantian term. To prove his point, he says that we apply attributes to words that just don't fit with the "thing in itself". For example, in german language, "kitchen", Küche is a female noun. His point is, just how arbitrary is a neutral object to be gendered.

 

[wuliheron]

Well, to start a linguistics debate on Descartes is to beg for a ginormous discussion on everything from Nietzsche to Wittgenstein.

Nonsense, the OP asked a specific question:

"Does this common phrase which is often seen as self-evident provide solid proof to remove the doubt of "I" (in your case, yourself) existing."

Either you consider it rock sold evidence or you don't and only the psychic network might debate the issue of how you feel.

 

[Maui]

In following the rules, I will explain in detail what exactly is up for debate here, so this thread will not be locked.

"I Think Therefore I Am", a common phrase (maybe the most common phrase), was written by Rene Descartes in the 1600's in his book Meditations II. In Meditations I, he "demolished" the certainty of anything existing. His reasoning was that there is no way to prove that his thoughts are deluded or being deceived, as humans have been wrong. Some of the examples he provided was you could not disprove that there is an evil supernatural being tricking the human mind or simple everyday optical illusions that trick the mind. The next day in Meditations II, he wrote that there is one thing that he could be completely certain of, that he existed. His logic was that doubts of certainty were because of deluded thoughts. If there are thoughts to delude, thoughts exist, and "I" (in this case, Descartes) is a thinking being that exists.

Question: Does this common phrase which is often seen as self-evident provide solid proof to remove the doubt of "I" (in your case, yourself) existing.

---

My personal opinion:

Essentially descartes’ proof is:
X is true. Y is true. Therefore, X is true.

His argument is circular. "I think therefore I am" could also be "I am therefore I think".

It’s the same thing as to say unicorns are pink, therefore unicorns surely exist. How could something be pink if it doesn’t exist. It’s tautological. It’s the equivalent of saying apples are red and they are delicious, therefore apples are surely red.

You can replace the word think with ANYTHING. I eat therefore I exist. I dream therefore I exist. I walk therefore I exist. There’s no difference of what you say.

Philosophy is a part of linguistics. We use words, as our only means, to try to prove our ideas to other people. There is so many limitations to language. We may exist, but we are unable to use words to prove it.

Your thoughts?

This is a consensual reality and all 'proofs' require that you accept certain unprovable propositions as axioms(as have done others). I would challenge solipsism on the grounds that as much stupidity as seen in our reality would be a challenge for me to come up with. Same with all the horror and injustice found in reality. This doesn't disprove solipsism, only that certain versions(those claiming that i am the inventor of my own reality) are much less likely.

 

[daveb]

If it works for anything its because Descartes did not provide a rigorous definition for "I" and, as Ryan points out, it has to do with the "feeling" of existence. Its a nice compelling argument, but so is the idea the Earth is flat and like the idea the Earth is flat there exists endless evidence to the contrary.

The Earth is locally flat, so maybe we locally exist?

 

[wuliheron]

The Earth is locally flat, so maybe we locally exist?

That could also be rephrased as, "The question has no demonstrable meaning outside specific contexts." Certainly we seem to exist in some sense and there is obviously something we refer to as "I", but Descartes was trying to make some sort of sweeping metaphysical argument.

 

[Char. Limit]

Aren't you misjudging Descartes' argument? His original premise was "I doubt", and he did. He doubted his own existence. Then he went "Since I am doubting, this must mean I am thinking, because doubt is a type of thought." Okay, so you're thinking. However, you cannot have a non-existent being that nevertheless thinks. So therefore, since he's thinking, he must exist.

 

[wuliheron]

Aren't you misjudging Descartes' argument? His original premise was "I doubt", and he did. He doubted his own existence. Then he went "Since I am doubting, this must mean I am thinking, because doubt is a type of thought." Okay, so you're thinking. However, you cannot have a non-existent being that nevertheless thinks. So therefore, since he's thinking, he must exist.

Personally I find it rather bizarre to think any animal could actually doubt its own existence. Pretend to, sure, but not really doubt its own existence.

 

[Ryan_m_b]

Personally I find it rather bizarre to think any animal could actually doubt its own existence. Pretend to, sure, but not really doubt its own existence.

It happens, Cotards syndrome can sometimes manifest in patients as a distinct belief that they are dead and no longer exist. You can even say to these patients "do you exist" and they say "no I'm dead" even though they acknowledge they can see themselves and speak to you.

 

[wuliheron]

It happens, Cotards syndrome can sometimes manifest in patients as a distinct belief that they are dead and no longer exist. You can even say to these patients "do you exist" and they say "no I'm dead" even though they acknowledge they can see themselves and speak to you.

Believing you are dead is one thing, but nonexistent is beyond conceptualization.

 

[phinds]

I commend to all the story of Descarte's end. He went to a tavern with some friends and after several rounds, when asked by the barmaid would he like another ale, he said "oh, I think not" and he instantly ceased to exist.

 

[Ryan_m_b]

Believing you are dead is one thing, but nonexistent is beyond conceptualization.

Conceptualising nonexistance yes but it's entirely possible for a patient to believe that they do not exist due to a psychiatric disorder.

 

[DaveC426913]

Personally I find it rather bizarre to think any animal could actually doubt its own existence. Pretend to, sure, but not really doubt its own existence.

That's kind of the point here.


A non-existent thing can categorically not doubt anything. If doubt is occurring, the thing doing the doubting - whatever that thing is - exists. And whatever it is doing the doubting is what Descartes calls "I".

 

[wuliheron]

That's kind of the point here.

A non-existent thing can categorically not doubt anything. If doubt is occurring, the thing doing the doubting - whatever that thing is - exists. And whatever it is doing the doubting is what Descartes calls "I".

So, you know a lot of non-existent things personally I take it?

 

[DaveC426913]

So, you know a lot of non-existent things personally I take it?

Mm... no. But I can still categorically state that they cannot do any doubting.

 

[Maui]

Conceptualising nonexistance yes but it's entirely possible for a patient to believe that they do not exist due to a psychiatric disorder.

What about those who believe they exist? Wouldn't it be less dubious to say - something appears to be happening, instead of using loaded words like "I"(which undergoes changes all the time, is hard to define and determinists hold that it doesn't exist in and of itself)?

As a continuation to Decrates' doubt, it is in principle possible(and likely?) that we all share a psychiatric disorder which, because of sheer the number of cases(7 billion), has proved to be the norm(and which we call the reality as we agree on it). There'd be no way to know, as a disorder has to be contrasted to the 'normal' state, which we have assumed to be the prevalent case. And only certain doubts like not being able to understand uncaused events or certain conceptual problems, can give a reason to consider such a scenario and that a different hypothetical breed could have fared better in some circumstances.

 

[ThomasT]

In following the rules, I will explain in detail what exactly is up for debate here, so this thread will not be locked.

"I Think Therefore I Am", a common phrase (maybe the most common phrase), was written by Rene Descartes in the 1600's in his book Meditations II. In Meditations I, he "demolished" the certainty of anything existing. His reasoning was that there is no way to prove that his thoughts are deluded or being deceived, as humans have been wrong. Some of the examples he provided was you could not disprove that there is an evil supernatural being tricking the human mind or simple everyday optical illusions that trick the mind. The next day in Meditations II, he wrote that there is one thing that he could be completely certain of, that he existed. His logic was that doubts of certainty were because of deluded thoughts. If there are thoughts to delude, thoughts exist, and "I" (in this case, Descartes) is a thinking being that exists.

Question: Does this common phrase which is often seen as self-evident provide solid proof to remove the doubt of "I" (in your case, yourself) existing.

---

My personal opinion:

Essentially descartes’ proof is:
X is true. Y is true. Therefore, X is true.

His argument is circular. "I think therefore I am" could also be "I am therefore I think".

It’s the same thing as to say unicorns are pink, therefore unicorns surely exist. How could something be pink if it doesn’t exist. It’s tautological. It’s the equivalent of saying apples are red and they are delicious, therefore apples are surely red.

You can replace the word think with ANYTHING. I eat therefore I exist. I dream therefore I exist. I walk therefore I exist. There’s no difference of what you say.

Philosophy is a part of linguistics. We use words, as our only means, to try to prove our ideas to other people. There is so many limitations to language. We may exist, but we are unable to use words to prove it.

Your thoughts?

I think Descartes overcomplicated it. "I am" or "I exist" are tautological statements in that being or existence follows from the meaning of "I".

 

[DaveC426913]

I think Descartes overcomplicated it. "I am" or "I exist" are tautological statements in that being or existence follows from the meaning of "I".

But you don't get great truths by saying 'we know it's true because that's what the word means'.

You're right yours is tautological, thus not much use. And we wouldn't be quoting it 4 centuries later.

 

[ThomasT]

But you don't get great truths by saying 'we know it's true because that's what the word means'.

Well, what does the word "truth" refer to?

You're right yours is tautological, thus not much use. And we wouldn't be quoting it 4 centuries later.

Right. At least not the way I'm currently considering it. EDIT: To clarify, if "I" has a pointable referent, then I exist. Don't I?

 

[DaveC426913]

EDIT: To clarify, if "I" has a pointable referent...

Yes, but how do you know it does?

Descartes is identifying the one thing that can't be explained away: the thinking.

 

[ThomasT]

Yes, but how do you know it does?

I'm pointing to it. Apparently, it resides somewhere in my head. At least it seems that way. Should I consider this to be some sort of illusion or delusion? And what do those terms mean if we don't have some criterion of reality?

Descartes is identifying the one thing that can't be explained away: the thinking.

And what is the recognition of "I" ... "me"? Does that require what we call thinking?

 

[DaveC426913]

I'm pointing to it. Apparently, it resides somewhere in my head. At least it seems that way. Should I consider this to be some sort of illusion or delusion?

Your pointing finger and your head can both be illusions, yes.

But the thing being ... um ... illuded ... - the thoughts - cannot be.

 

[Rayquesto]

Prove:
I think therefore I am => I think 'too much' therefore I am 'too much'

 

[ThomasT]

Your pointing finger and your head can both be illusions, yes.

Could be. Yes. But so far they're confirmed by my friends here. Of course they could be illusions as well. And, even if they're real, their recounting of their experiences could be illusions, or lies. And so on. So what determines truth or reality? Are the words "truth" and "reality" meaningless? Or absurdly ambiguous? Or do they mean something that we can all point to and agree that's there? What's the criterion? What do the words "truth" and "reality" refer to?

But the thing being ... um ... illuded ... - the thoughts - cannot be.

Thoughts, mental visions, can't be illusions? Then what does the word "illusion" refer to?

 

[DaveC426913]

Could be. Yes. But so far they're confirmed by my friends here. Of course they could be illusions as well. And, even if they're real, their recounting of their experiences could be illusions, or lies. And so on. So what determines truth or reality? Are the words "truth" and "reality" meaningless? Or absurdly ambiguous? Or do they mean something that we can all point to and agree that's there? What's the criterion? What do the words "truth" and "reality" refer to?

This is Descartes' point, yes. Nothing can be trusted. Nothing.

The only thing he knows cannot be an illusion is that he is doubting. And that means he must exist.

Thoughts, mental visions, can't be illusions? Then what does the word "illusion" refer to?

This is getting meta

Yes, thoughts can be illusions. But the thing that had the thoughts cannot.

 

[ThomasT]

This is Descartes' point, yes. Nothing can be trusted. Nothing.

The only thing he knows cannot be an illusion is that he is doubting.

Why can't that be an illusion as well? Indeed, that would seem to be a prime candidate for being an incorrect interpretation or apprehension of reality ... whatever that is. How could he/we know?

And that means he must exist.

I think Descartes existed, just as I think I, and you, exist. We're back to my premise. I think he overcomplicated it.

This is getting meta

Meta is ok. When it gets to ubermeta then we need to take a time out and call for pizza.

Yes, thoughts can be illusions. But the thing that had the thoughts cannot.

I thought you said that it's the thoughts that can't be illusions.

I'm not trying to be inordinately argumentative here. But I have no doubt that Descartes was, and that you are and I am. Am I wrong in thinking that way? And if that's not wrong, then why is it right?

 

[DaveC426913]

I think Descartes existed, just as I think I, and you, exist. We're back to my premise. I think he overcomplicated it.

You take that on faith. It's a cop out.

Humankind has struggled with that unsatisfactory result for ages. Descartes said: the buck stops here.

I thought you said that it's the thoughts that can't be illusions.

No, it's the thing doing the thinking.

I'm not trying to be inordinately argumentative here. But I have no doubt that Descartes was, and that you are and I am. Am I wrong in thinking that way?

For 99.99999% of our existence you'd be right.

Let me ask you this: as a cosmologist, would you be satisfied if we had a unified law that explained the entire universe, and it worked perfectly - except inside a black hole? We'll just take on faith that things work out OK there and look the other way. But our law covers EVERYTHING else.

OK, you could live with it. Could your descendants? Do you think after 400 yers, no one would bother solving that little piece?

Humankind has spent millenia being satisfied with 'I'm almost entirely sure my foot and that chair are real'. But the question never really goes away until it's answered.

 

[ThomasT]

You take that on faith. It's a cop out.

I think that I take that ... by definition/convention. There's no faith involved there as far as I can tell.

Humankind has struggled with that unsatisfactory result for ages.

That's not unsatisfactory. It's convention. It's a function of our apprehension and recording of what we call reality, and the way we communicate that.

Descartes said: the buck stops here.

Descartes said, "I think, therefore I am". It's a tautology. The "I am" is implied by the "I think". Descartes might just as well have said, "I am". Whereby, the "am" is implied by the "I".

No, it's the thing doing the thinking.

So, it's the thing doing the thinking that might be an illusion, but the thoughts themselves aren't or can't be illusions?

For 99.99999% of our existence you'd be right.

Well then why not 100%. Oh, I see, we're coming to that.

Let me ask you this: as a cosmologist, would you be satisfied if we had a unified law that explained the entire universe, and it worked perfectly - except inside a black hole? We'll just take on faith that things work out OK there and look the other way. But our law covers EVERYTHING else.

No, I don't think I'd be satisfied, but I might accept that black holes might represent an usurpassable limit to our knowledge..

OK, you could live with it. Could your descendants? Do you think after 400 yers, no one would bother solving that little piece?

Well, if it really was an unsurpassable limit, then I guess they'd have to learn to live with it. But I would suppose that they would try to solve it.

Humankind has spent millenia being satisfied with 'I'm almost entirely sure my foot and that chair are real'. But the question never really goes away until it's answered.

Isn't it just a matter of how we define the terms we use? And, wrt that, then my foot and that chair ARE real.

 

[wuliheron]

Mm... no. But I can still categorically state that they cannot do any doubting.

You can also categorically state the moon is made of cheese, but I prefer evidence myself.

 

[ThomasT]

Anything other than our sensory apprehension of the world is supposition, inference, invention, etc. I suppose that the fundamental reality of our universe might look quite different than the world of my sensory apprehension. But I don't suppose that it's evolving according to different fundamental dynamics, because that would make no sense ... to me anyway.

Back to Descartes. "I think, therefore I am" is a tautology. "I am" is a tautology. This follows from the definitions of the terms. We know that we exist via the conventional usage of those terms. There's no doubt, by definition. I exist. You exist. We exist. It's just how we communicate our experience. Any philosophical problems with this are, imho, pseudoproblems. And it was just this sort of thing that logical positivism intended to clarify. Which, afaik, it did.

 

[ThomasT]

Our existence is self-evident. Whatever Descartes had to say about it is, imho, superfluous.

 

[Maui]

I think that I take that ... by definition/convention. There's no faith involved there as far as I can tell.

That definition rests on assumptions that Decartes wasn't willing to make(for his argument). So yes, there is some faith involved from his POV.

That's not unsatisfactory. It's convention. It's a function of our apprehension and recording of what we call reality, and the way we communicate that.

That would not be rigorous proof by the standards Decartes set.

Descartes said, "I think, therefore I am". It's a tautology. The "I am" is implied by the "I think". Descartes might just as well have said, "I am". Whereby, the "am" is implied by the "I".

Not according to latest neuroscience. "I think" carries much less weight(and appears to come after the fact) than "causal deterministic processes determine the brain's thoughts". If one's thoughts are predetermined and resultant from processes over which 'you' have no control, would it make sense to say that the "I am" is implied by the "I think"?

 

[DaveC426913]

You can also categorically state the moon is made of cheese, but I prefer evidence myself.

Then you're in the wrong discussion and possibly the wrong forum.

You'll have to rely on logic here. No evidence is going to be forthcoming. Not the least of reasons because the very discussion is that all evidence is suspect.

 

[DaveC426913]

Back to Descartes. "I think, therefore I am" is a tautology.

No it isn't.

"I am" is a tautology. This follows from the definitions of the terms.

This is weak and Descartes rejected it. He knows it is a tautology.

We know that we exist via the conventional usage of those terms. There's no doubt, by definition.

So, if I define myself as stinking rich, I am?

 

[Jimmy Snyder]

So, if I define myself as stinking rich, I am?

I stink. Therefor I am rich.

 

[daveb]

I stink. Therefor I am rich.

I thought you were Jimmy?

 

[ThomasT]

No it isn't.

Ok, I think I understand why it's not a tautology. "I am" is a tautology, but "I think" isn't a tautology, and "I am" and "I think" are not equivalent, but "I think" is a subset of "I am", so if I think, then I am, or "I think, therefore I am."

Now I have to go back in the thread and Google/Wiki/Stanford/whatever to understand why "I cook, therefore I am" doesn't work the same way. (As might be evident, I do a lot more cooking than thinking.)

This is weak and Descartes rejected it. He knows it is a tautology.

I was thinking that the statement "I am" is self-evidently true because of the conventional usage/meaning of the terms involved. That is, saying that I doubt or can doubt my existence would seem to be a contradiction in terms given what "my being", "my existence", "I am" refer to.

So, if I define myself as stinking rich, I am?

I was saying that "my being" or "my existence" refers to my subjective experience, which I have no doubt about experiencing.

 

[wuliheron]

Then you're in the wrong discussion and possibly the wrong forum.

You'll have to rely on logic here. No evidence is going to be forthcoming. Not the least of reasons because the very discussion is that all evidence is suspect.

I beg to differ, the argument is about which types of evidence are less suspect then others, including what logical arguments.

 

[Char. Limit]

"I think therefore I am" is definitely NOT a tautology. The two statements aren't even equivalent. The converse of "I think therefore I am", "I am therefore I think" is definitely not true for everything.

 

[ThomasT]

"I think therefore I am" is definitely NOT a tautology.

Yes, I see that now.

The converse of "I think therefore I am", "I am therefore I think" is definitely not true for everything.

It's not necessarily true for anything, is it? That is, no particular mode of being is implied by being. Being doesn't imply thinking.

What I still don't get is why cooking doesn't imply being.

 

[Char. Limit]

Well of course "I cook therefore I am" is a valid statement. But, like Descartes had to prove he was thinking, you have to, I guess, prove that you're cooking. Descartes' method of proving he was thinking was to assert that he is doubting, which implies thought.

 

[ThomasT]

Well of course "I cook therefore I am" is a valid statement.

That's what I thought.

But, like Descartes had to prove he was thinking, you have to, I guess, prove that you're cooking.

How does one prove an experience?

Descartes' method of proving he was thinking was to assert that he is doubting, which implies thought.

I still don't get it. Does counting imply thought? Why is doubting special? Why is thinking special? Why not just "I experience, therefore I am"?

 

[ThomasT]

What do the words "being" and "existence" refer to? If the referent is our subjective experience, then I don't think that Descartes has proven anything beyond what's already evident.

 

[Ryan_m_b]

What do the words "being" and "existence" refer to? If the referent is our subjective experience, then I don't think that Descartes has proven anything beyond what's already evident.

I'm not sure if he was trying to prove anything, rather he was pointing out that the only thing we can be certain of is our existence. Everything about that existence can be faked but the fact that there is an existence cannot: you can convince an extant being everything but you can't convince a non-existent entity of anything.

It might seem evident but evidently for many it isn't.

 

[wuliheron]

What do the words "being" and "existence" refer to? If the referent is our subjective experience, then I don't think that Descartes has proven anything beyond what's already evident.

I don't believe proving anything new was the point to begin with. Descartes was attempting to create a new philosophical foundation upon which the emerging sciences of the day could distinguish themselves from the church. The issue was how to accomplish that while still working within the accepted cultural biases of the time. Hence, by focusing on the ego he found a way to exploit the dualistic bias of the culture and church to advance the sciences.

 

[DaveC426913]

...I don't think that Descartes has proven anything beyond what's already evident.

'Evident' is not enough. It's based on an assumption. He rejected assumptions.

Descartes believed that everything was based on assumptions. He set out to prove that nothing could be said at all without basing it on some assumptions that itwas real. In a sense, he set out prove that our existence was a tautology.Look at it from the other side of the coin. Assume absolutely everything is an illusion, craftily put in front of you. The world, everyone you know, your eyes, even your brain. All these things could be constructs, put in your mind to fool you into thinking they're "evident", as you call it. So we can trust none of them.

It's very Matrix-like.

But what Descartes realized is that, even if everything is an illusion, there is still something experiencing that illusion. Even if you Thomas, are a program in a computer, fed all your sensory input. There is still something that is experiencing that input.

No matter what it looks like, no matter what it's made of, it exists.

He is showing that your statement "I am" is not simply an act of defining something as existing, he can logically show it to be true.

...

I think I'm not really adding anything more to this thread except repeating myself.

Perhaps one thing to add:

...These things are evident to us now. One big reason why is because people like Descartes did ground-breaking work that our knowledge is based on.

Perspective in artwork is self-evident in the modern world. We know objects that are farther away are smaller than objects nearby. But that wasn't self-evident before da Vinci and his contemporaries came along and defined it -took the mystery out of it - that it became self-evident after that.

There are other examples in science, such apples falling to the Earth and the correlation between force, mass and acceleration that we wonder how they could not have known them at some time in the past.