That an interesting thought, but I'm unclear why this is a significant problem for materialism. There are lots of thing that we can doubt, but which we nevertheless continue to believe because we have good reason to. Lacking complete certainty isn't that much of a problem is it? Unless one's project is to put one's philosophy beyond any doubt at all, perhaps.

...or we could flip this argument and say that the poverty of Cartesian Dualism is that it can't be sure of the existence of the computer on which you are reading this post.

In conclusion, we can be certain of only one thing - the existence of minds - and we can always doubt the reality of the physical world, materialism. — TheMadFool

This suggests that you might characterise materialism as the belief that the the physical world is real. I don't think this adequately distinguishes materialism from any other monism.

For me, materialism is most accurately understood as a theory of consciousness. I think what people most commonly mean by 'materialism' is the view that consciousness is a latecomer to the universe, and the stuff of the universe (particles, fields, whatever) started out without consciousness, and that consciousness only developed as a result of a very particular set of circumstances happening to occur. I think what people most commonly mean by 'materialism' is pretty much 'emergentism'. But I'm happy to be corrected by those who identify as materialists.

Descartes proved, beyond the shadow of a doubt in my humble opinion, that the physical could be an illusion, unreal but, the mind, for certain, is not. Cartesian skepticism undermines materialism by showing the reality of the physical can be questioned but you couldn't doubt the existence of the mind.

In conclusion, we can be certain of only one thing - the existence of minds - and we can always doubt the reality of the physical world, materialism. — TheMadFool

If so, then the question becomes, Why is the physical world an illusion? If the external world isn't real, then why does it appear to be a physical world?

Other minds are only known by perceiving physical bodies. So other minds in this physical world would be part of the "illusion". There would only be your mind - solipsism. That is essentially all Descartes' extreme skepticism "proves".

The existence of Material Being is dubitably certain and contingent, whereas, the existence of Thinking Being is indubitably certain and contingent. Both types of Being, the dubitable and the indubitable, are CONTINGENT because they are experienced as "always being open to the possibility of complete cessation and non-existence."

Unfortunately, there is no NECESSARY being that can be experienced by humans which is experienced as "always being closed to the possibility of complete cessation and non-existence."

If, instead, Descartes had shown us how we could not doubt the NECESSARY existence of either thought or matter, then that really would have been an astounding discovery!

You see, it's not so much the INDUBITABLE CERTAINTY of the existence of what he is talking about that's crucial as it is the NECESSARY, rather than the CONTINGENT, existence of what what he is talking about.

But, as I said, it is impossible for humans to personally experience such a being.

@bert1@Banno@Harry Hindu@charles ferraro
The point is simple: materalism is reportedly a position of skepticism, skepticism of things belonging to the category of the immaterial and the like. I'm unsure how it all began but there's a very strong association between materialism and skepticism in this day and age and perhaps in the past too - it's as though people are under the impression that materialism is an offshoot of skepticism e.g. modern skeptics are fond of referencing and turning to science which, we all know, is the byword for materialism. What I mean to show here is that this is an egregious error; skepticism actually leads you away from, rather than to, materialism: we can doubt the reality of the physical/material world but we can never doubt the existence of our minds.

What I mean to show here is that this is an egregious error; skepticism actually leads you away from, rather than to, materialism: we can doubt the reality of the physical/material world but we can never doubt the existence of our minds. — TheMadFool

Don't you have to be a bit more conservative and say that you can't doubt the existence of your own mind. You can doubt the existence of mine. Descartes gives you permission.

Don't you have to be a bit more conservative and say that you can't doubt the existence of your own mind. You can doubt the existence of mine. I give you permission. — Nils Loc

Does the cogito ergo sum make sense to you? If it does, then you exist.

...all of this derives from Descartes' orgy of unreasonable doubt.

Does the cogito ergo sum make sense to you? — TheMadFool

What can one do with this foundational intuition if everything else is to be doubted? You're giving me Cartesian anxiety.

If we move upwards from Descartes dirty basement (too much of the ol' philosophia), we can all put our clothes back on and have reasonable doubts in the living room.

We can doubt every particular about the physical world, but we can't doubt that there is some physical world at all. The physical world is the stuff that's available to empirical experience. I can't imagine not having any empirical experience at all -- that would just be to not imagine anything.

I wrote in another thread recently:

Descartes famously attempted to systematically doubt everything he could, including the reliability of experiences of the world, and consequently of the existence of any physical things in particular; which he then took, I think a step too far, as doubting whether anything at all physical existed, but I will return to that in a moment. He found that the only thing he could not possibly doubt was the occurrence of his own doubting, and consequently, his own existence as some kind of thinking thing that is capable of doubting.

But other philosophers such as Pierre Gassendi and Georg Lichtenberg have in the years since argued, as I agree, that the existence of oneself is not strictly warranted by the kind of systemic doubt Descartes engaged in; instead, all that is truly indubitable is that thinking occurs, or at least, that some kind of cognitive or mental activity occurs. I prefer to use the word "thought" in a more narrow sense than merely any mental activity, so what I would say is all that survives such a Cartesian attempt at universal doubt is experience: one cannot doubt that an experience of doubt is being had, and so that some kind of experience is being had.

But I then say that the concept of an experience is inherently a relational one: someone has an experience of something. An experience being had by nobody is an experience not being had at all, and an experience being had of nothing is again an experience not being had at all.This indubitable experience thus immediately gives justification to the notion of both a self, which is whoever the someone having the experience is, and also a world, which is whatever the something being experienced is.

One may yet have no idea what the nature of oneself or the world is, in any detail at all, but one can no more doubt that oneself exists to have an experience than that experience is happening, and more still than that, one cannot doubt that something is being experienced, and whatever that something is, in its entirety, that is what one calls the world.

So from the moment we are aware of any experience at all, we can conclude that there is some world or another being experienced, and we can then attend to the particulars of those experiences to suss out the particular nature of that world. The particular occasions of experience are thus the most fundamentally concrete parts of the world, and everything else that we postulate the existence of, including things as elementary as matter, is some abstraction that's only real inasmuch as postulating its existence helps explain the particular occasions of experience that we have. — Pfhorrest

...all of this derives from Descartes' orgy of unreasonable doubt. — Banno

Why unreasonable?

What can one do with this foundational intuition if everything else is to be doubted? You're giving me Cartesian anxiety.

If we move upwards from Descartes dirty basement (too much of the ol' philosophia), we can all put our clothes back on and have reasonable doubts in the living room. — Nils Loc

What constitutes a reasonable doubt?

I consider something unreasonable iff it entails a contradiction or is in violation of the rules of deduction. Do you see any of the above in Descartes' inference?

Unreasonable doubt is rejecting everything until it can be proven from the ground up. This is unreasonable because nothing can be proven from the ground up, so that entails automatically rejecting everything forever.

Reasonable doubt is being willing to reject something in case reason to reject it should arise. Absent that, it's reasonable to believe whatever just seems most likely to you, even if you can't prove it from the ground up, so long as if there is reason to reject it, you will.

Unreasonable doubt is rejecting everything until it can be proven from the ground up. This is unreasonable because nothing can be proven from the ground up, so that entails automatically rejecting everything forever. — Pfhorrest

But Descartes proved his own existence, and by extension, the existence of anyone else capable of making the cogito ergo sum argument.

The way our experience of being in the world is constituted precludes any absolute certainty. On the other hand both Descartes and Hume used front doors when departing buildings and not 4th floor windows. It doesn't seem very fruitful to doubt the solidity and predictability of the material world.

But Descartes proved his own existence, and by extension, the existence of anyone else capable of making the cogito ergo sum argument. — TheMadFool

Except he didn’t; see Gassendi and Lichtenberg mentioned above.

Or else, to the same extent that he proved that some self exists, he also proved that some world exists, but he proved no particulars about either, and left no leverage for ever doing so.

Why unreasonable? — TheMadFool

Well, what reason did Descartes have for such doubt? Why do you need reasons for confidence, but will doubt without such reason? What leads to this curious asymmetry?

Descartes proved, beyond the shadow of a doubt in my humble opinion, that the physical could be an illusion, unreal but, the mind, for certain, is not. Cartesian skepticism undermines materialism by showing the reality of the physical can be questioned but you couldn't doubt the existence of the mind. — TheMadFool

I'm afraid I have to doubt your certainty. Descartes showed that he had a brain, sure, but he has failed to show that the voice he could hear inside his head originated with him.

a thought experiment: you are lying on a beach. you can see the waves crashing on the shore. you can hear those waves crashing on the shore. in your mind you associate the sound you can hear with the waves you can see, so that it appears to you that the sound is created by the waves. this clearly shows that sounds inside your head can, or may, or possibly might sometimes, originate outside your head.

now close your eyes, and listen to the waves crashing on the shore. absent the visual signal, you are unable to tell whether the sound has an origin interior to or exterior to your head. there is simply no way to tell.

now explain how Descartes is able to prove, in your own words, "beyond the shadow of a doubt," that the voice he can hear is his?

I really don't have a problem if you want to claim that this is the most probable, the most likely, scenario, and that alternatives sound more like science fiction than philosophy. but to claim that Descartes "proved" this is simply not true.

Descartes showed that he had a signal processing organ inside his head that we call the brain. but you cannot prove where any of those signals originate.


Kaarlo Tuomi

The way our experience of being in the world is constituted precludes any absolute certainty. On the other hand both Descartes and Hume used front doors when departing buildings and not 4th floor windows. It doesn't seem very fruitful to doubt the solidity and predictability of the material world. — hwyl

Descartes was a dualist. I'm only concerned about difference in the level of certainty regarding his belief in minds and the physical world. The cogito ergo sum argument is a watertight, foolproof argument for the existence of minds. I've never heard of a Cartesian or otherwise physical counterpart to the cogito ergo sum argument and, for sure, it's because there is none. We're less certain of the physical than we are of the mind or, conversely, we're absolutely certain of the mind but serious doubts remain about the existence of a physical reality.

Except he didn’t; see Gassendi and Lichtenberg mentioned above — Pfhorrest

Read the sentence: I think, therefore I am in your mind or aloud. If you fail to see Descartes' point then you would be saying that thinking doesn't entail a thinker (a mind that does the thinking) and I'll have to ask what's that thing that's doing the thinking? The correct answer to that question is, if you must be as conservative as possible, something but it's precisely this something that thinks we understand as mind.

Well, what reason did Descartes have for such doubt? Why do you need reasons for confidence, but will doubt without such reason? What leads to this curious asymmetry? — Banno

The reason for Descartes' doubt is simple - it is possible (to doubt).

that the voice he can hear is his? — Kaarlo Tuomi

That's not a problem. Notice there is something that can be confused, baffled, misled, deluded. That something is Descartes or you or me or anyone else. That there's an illusion means there's something, the mind, that perceives this illusion.

The reason for Descartes' doubt is simple - it is possible (to doubt). — TheMadFool

That's a singularly poor reply. It is also possible to be confident.

That's a singularly poor reply. It is also possible to be confident. — Banno

I see no violation of logic.

I'm not surprised.

I still haven't gotten the hang of the quote function here - bit of a counter intuitive platform...

Anyway, not that it is important at all, and I can happily live with absolute logical proof of the existance of my mind (if not for anyone else's), but surely there is still room for some doubt. I mean there is something there pretty conclusively, but we can never be absolutely sure of what it is. Some random noise creating a momentary illusion of a cohesive mind. Something exists, maybe it's my mind. And anyway, I really don't think any of this as any crucial matter. In all important things - and maybe even in this - there will always be room for doubt, mostly very insignificant and unimportant room but still.

The point is simple: materalism is reportedly a position of skepticism, skepticism of things belonging to the category of the immaterial and the like. — TheMadFool

What is the difference between material and immaterial? If you're willing to be skeptical of how the world is vs how it appears, then why aren't you skeptical of how the mind is vs how it appears? You're inconsistently applying your skepticism. What makes Descartes believe that his demon could only be fooling him about the nature of the world and not also his mind? And then what is the nature of the demon itself?

The correct answer to that question is, if you must be as conservative as possible, something but it's precisely this something that thinks we understand as mind. — TheMadFool

Sure, and the something that is the object of that thought is the world. All the details if the world are highly dubitable, but then so are all of the details if the self.

there will always be room for doubt, mostly very insignificant and unimportant room but still. — hwyl

There lies the rub: to doubt there must be a doubter. You can doubt anything but you can't doubt the existence of the thing that doubts.

What is the difference between material and immaterial? If you're willing to be skeptical of how the world is vs how it appears, then why aren't you skeptical of how the mind is vs how it appears? You're inconsistently applying your skepticism. What makes Descartes believe that his demon could only be fooling him about the nature of the world and not also his mind? And then what is the nature of the demon itself? — Harry Hindu

See my reply to hwyl above. If there's some kind of deception going on, it follows there's something that's being deceived and that's the thinking part. The skepticism is universal but the thing is to be skeptical implies the existence of a skeptic.

but then so are all of the details if the self. — Pfhorrest

The existence of the doubter is certainly beyond doubt.

The existence of the doubter is certainly beyond doubt. — TheMadFool

Only to the same extent as the existence of some world or another the details of which are being doubted.

All the details of the doubter are equally in doubt. Who am I? I have a bunch of memories and thoughts and feelings but are they really mine, or is someone else feeding them in to me? Someone is doubting when I doubt and I identify with that doubted but who is that exactly? What are they ("I"?) like? All of that is in doubt as much as anything about the world is in doubt.

Only to the same extent as the existence of some world or another the details of which are being doubted.

All the details of the doubter are equally in doubt. Who am I? I have a bunch of memories and thoughts and feelings but are they really mine, or is someone else feeding them in to me? Someone is doubting when I doubt and I identify with that doubted but who is that exactly? What are they ("I"?) like? All of that is in doubt as much as anything about the world is in doubt. — Pfhorrest

That's correct of course but the point is this isn't about the who? - the personhood of the doubter, although I suspect it'll be important later on; this is about the what? as in physical or non-physical nature of the "something that's doing the thinking". Given that we can cast doubt on the reality of the physical, the entire human body could be an illusion, including the brain but the part that's doing the thinking can't be doubted regarding its realness. If the brain and the body could be an illusion and there certainly exists something that's doing the thinking, is it proper to attribute something certain, the thinker, to something dubitable, the brain/body? For instance, if I know for certain that you exist, it's ridiculous, if not insane, for me to think you're someone who could be an illusion, say a person that I meet in my dreams.

In conclusion, we can be certain of only one thing - the existence of minds - and we can always doubt the reality of the physical world, materialism. — TheMadFool

Augustine in City of God said:

I am most certain that I am and that I know and delight in this. In respect of these truths, I am not at all afraid of the arguments of the Academicians [i.e., skeptic philosophers], who say, “What if you are deceived?” For if I am deceived, I am. For he who is not, cannot be deceived; and if I am deceived, by this same token, I am. And since I am if I am deceived, how am I deceived in believing that I am? for it is certain that I am if I am deceived. Since, therefore, I, the person deceived, should be, even if I were deceived, certainly I am not deceived in this knowledge that I am.

...anticipating Descartes by quite a few centuries.

I have a bunch of memories and thoughts and feelings but are they really mine, or is someone else feeding them in to me? — Pfhorrest

I take your point, but remember the saying in Latin is: cogito ergo sum. In English, it is expressed as 'I think, therefore I am', but in an inflected language, it is much nearer to 'thinking, therefore being'. Which is also nearer the point.

'The soul' it has been said, 'is whatever it is that can say "I am" '.

Of how many types of beings is that the case?