Two Mistakes and Scepticism

Originally, I wanted to call this three mistakes, but Kant is a tougher nut to crack than that (I can say that it’s his emphasis on inner representation that’s the problem but it takes a while to see that.). I am not saying that Descartes and Locke aren’t worthy of reading, I think it is absolutely necessary to read them (if you’re interested in this stuff, that is), but pointing out what’s wrong can just as easily be seen as a sign of respect, even love, as it can be seen as a sign of disrespect.

First mistake: Descartes argued that since we can be wrong about any one belief, it follows that all of our beliefs can be false. The problem is that it doesn’t follow at all. In order to determine that one of our beliefs is false, we have to accept a large part, even most, of our other beliefs to be true. Otherwise, we wouldn’t be able to determine the falseness of that one belief. If we aren’t willing to consider that some of our beliefs our false or can be false, then we can’t at the same time believe they are true. 1+1=2 is true but only if we accept that 1+1=3 or 1+1=0 are false. The true and the false are intricately linked.

Second mistake: Locke confuses explanation with justification. It simply doesn’t matter how we come to see the world when it comes to our accuracy with respect to the world. You can explain to me how photons turn into electric signals which my brain interprets for as long as you want, it simply doesn’t follow that you can therefore put the fact that I’m looking at a computer monitor at this moment into question. I may or may not be actually seeing a computer monitor right now (it is possible that I’m wrong), but no amount of explaining how I see a monitor justifies the doubt. If I’m travelling down the Pacific Coast Highway, you can’t explain away the Pacific ocean by explaining to me the intricacies of the internal combustion engine.

If you accept these things as mistakes, we move a long way toward realizing that we just aren’t really cut off from the world, we are in it.

We’re on the same side. I’m trying to refute Cartesian scepticism here; you follow Quine, I’m attempting a kind of synthesis between Rorty and Davidson (both of whom agree with Quine here).

I see no reason to see that I’ve put any particular weight on see. If I’m drugged, the monitor is still there or not. I’m either mistaken or not. It doesn’t matter how I get there, drugged or not. If I later determine that I’m mistaken, one of the reasons for being mistaken might be halicinogens (though it could just as easily be something else). The latter part here seems to depend on the ‘inner representation’ mistake. I’ll have to get to that later. Or maybe I can just use shorthand here: I follow Davidson’s emphasis on the distal object rather than Quine’s emphasis on stimulus data.

brad – good topic, hopefully you don’t mind if i step in here to ask you a question. i agree with your two arguements, and am interested in the refutation to descartes. you ended the post with:

do you view that the quest to know the one “right/truth” as an idea that must be based on some form of cartestian dualism? i assume this is what you are trying to reject in your arguements – is this the ultimate point that you are trying to make?

This is not quite what Descartes’ was saying, it was more along the lines of this…

“You must examine all human knowledge and see if it can be doubted. If it is dubitable and so ‘infected’, then it must be mercilessly rejected as flawed. I asked myself where all human knowledge comes from. I decided there are only two sources of knowledge: our sense and our reason.”

Why was he this merciless?

“Imagine someone has some apples which he wishes to store in a basket. A wise man will make quite sure that all the apples are perfect – because if an apple does go rotten then it will eventually infect all the others. So, any apple that has even the slightest blemish has to be ruthlessly rejected as unsuitable.”

This is how Cartesian doubt works. Any ‘apple’ of knowledge that is finally left behind after this procedure would obviously be very special. It would be the real thing - guaranteed indubitable knowledge.

He doesn’t talk about true or false, but only what can be doubtable. While what he might examine could well be true, the fact that there’s something doubtable about it means he must reject it. This is because Descartes searchs for perfect truth; it must be 100% and not doubtable. Even if there’s only a 0.01% margin for doubt this is too much for him it must be considered flawed. I’m not saying this is the best way to search for truth, but coming from a Christian background he was used to talking about truth in absolute terms.

Descartes saw knowledge coming from two sources the Material World through our 5 senses and things like Maths and Logic comes through our Reason. So in search of what could be doubtable without having to examine everything in the world, why not see if what we use to carry out our experiments is doubtable (i.e. Our 5 Senses and Reason).

Can are 5 senses be doubted, well as far as Descartes is concerned the answer is yes. One example he used was, “if you place a stick into water is appears to be bent, but if we remove the stick, it’s not the case. The water gives the appearance of a bent stick.” Because our sense can be fool there is an amount of doubt when we use them to examine anything in the external world, so we must mercilessly reject our senses as flawed. While he doesn’t believe they lie always or that they are false, only that they can be doubtable and in search of perfect knowledge we can’t start to build knowledge on top of a doubtable source.

He then goes on to talk about how other things might be fooling us like: We could be dreaming, or being a religious man, he thought an invisible demon might be tricking us. It got to a point where he believe everything could be doubtable… till…

While going through this process of rigorous doubt, Descartes eventually discovered something rather extraordinary. What he realised was that there was always one thing that he could never doubt – the fact that he was doubting or thinking. And thinking just can’t happen in mid-air. There has to be a consciousness or mind doing it, so Descartes can’t doubt that he exists. Hence the famous Cogito ergo Sum, I think therefore I am”. Or perhaps more accurately: There are thoughts, so there must be a mind. So while he could pretend that he had no body and that there was no world… He could not pretend that he didn’t exist. By the fact that to doubt a mind requires a mind.

Honestly, I wasn’t sure what to do with that ‘must’. Certainly, I want to go after Cartesian dualism; yes, I want to go after essentialism – "the quest to know the one ‘right/truth’-- but I’m not sure the two are synonymous. That last sentence is funny. Ultimate points? I don’t make ultimate points.

Pax Vitae:

Well, what can I say? Your description still falls under my critique and adds to it further. You want to focus on doubt, but if doubt is enough to get rid of any particular belief, the mistake is, to me, even more obvious. One cannot doubt any particular belief such as:

without first accepting the undoubtability (I would say truth here) of many, many other things. He accepts the undoubtability of the stick, of water, of the difference in view between the stick in water and the stick in air at the same time, of things being bent etc.

Any and all examples of doubt rely on the undoubtability of many, many other things. It is certainly true that you can doubt any particular thing, but it is impossible to doubt these things without accepting most of the other things as undoubtable at that time. You can’t doubt everything at the same time, you can assert it but that doesn’t mean much. Try finding an example where this is wrong.

Now, you say (following Descartes):

But this is simply not understandable without first accepting many, many other things as true (tired of writing undoubtable). The invisible demon cannot trick us without first accepting many, many things that we already accept as true. You cannot trick a six week old infant, you cannot trick me by speaking tenth century Chinese. In order to trick me, you have to accept many of the things I hold to be true.

Therefore, the demon simply cannot trick me about everything at the same time.

Yet still more, his magic answer doesn’t hold either. You say you can’t doubt the doubting, but of course you can. A parrot or a computer says or computes things without presumably knowing what they are. Why not us? Why not think that it was the invisible demon who put those doubts inside of you and you, in fact, didn’t think them? Given that demon’s abilities, it certainly seems plausible. Actually, I can give plenty of examples where this is true enough, “I thought I loved her but I didn’t,” “I thought I was hungrier than I was” etc.

So how do you get out of this? It’s easy, you posit what we call Cartesian dualism, you assume, no matter what, that you can’t be wrong about your thoughts as an axiom and then proceed to explain that your thoughts aren’t really your thoughts, that there is some secret, magic language that gets it right even if your actual thoughts get it wrong and so on and so on.

And that’s the mistake in contention here.

“He accepts the undoubtablity of the sick,” No he doesn’t, you’ve missed his point. What he is trying to show is that when he views a straight stick outside of water it appears straight, but when the same stick is in water, appears bent. Nothing in the way his eyes work have changed between the two tests. He says because I can see the stick to be both bent and straight means there’s things in the external world that can cause us to be misled about our understanding of external objects. The only thing he believes that is indubitable is ‘I think’. Nothing else!

A more contemporary example would be like the movie the Matrix. Neo believe he lives in the real world, until he meets Morpheus (don’t know the correct spelling). He then shows Neo that the world he lives in is just an illusion, a computer generated reality. What Descartes is saying, if I can doubt my own sight then I can never be 100% sure of what I see is true. Descartes is searching of Perfect Truth, and because his sight can be doubted he can’t be sure of its truth.

I’m not saying Cartesian Dualism is right, as it’s clearly wrong. But the point of it was to show we couldn’t just accept what we see and hear as truths in themselves, because there is a case for doubting them.

I believe your logic here is flawed. All that doubt means is it could be false, it never implies this based off the evidence of an indubitable source. The only thing Descartes believes that is indubitable is “I think and I have thoughts.” I agree Descartes is wrong about Dualism, but for different reasons.

Yes, “accept as true” but that’s Descartes point! We can accept them as true, but we could have been tricked into believing them to be true! There’s doubt!

He believes we need to be able to think before we can even begin to doubt.

It’s not what you thought, but the fact you can have these thoughts that is indubitable.

I think inadvertently you have just proved Descartes right about total scepticism! You’ve claimed all can be doubted, so truth in its most perfect form can never be found. Hehe, how ironic. Even Descartes didn’t doubt enough to see this!

But that being said, I think Descartes would retort as follows: “The fact that you can see the demon’s thought requires us to have a consciousness or at least be conscious of what the demon is thinking. While we might not directly partake in the process of thinking or choosing what is thought about, we are aware of the thoughts, so we must have a reality and have a mind. Otherwise it’s only the demon tricking himself.” Like I said in my last post:

“If knowledge has to be appropriated by the mind and not the senses, what kind of guarantee can we have that we are not thinking absolute nonsense?” This is why God is included in Descartes proof.

Like I said he’s not 100% correct so is doubtable and in being doubtable he becomes 100% right about his argument. That all is doubtable, except for the fact I can experience thoughts, as this requires a mind (consciousness), this I cannot doubt.

Let me rephrase the argument (and hope make it clearer):

1. Doubt is the ability to put some truth into question, “I doubt that” means “I’m not sure that that is true.”

2. It certainly requires thought, but it also requires active thought in order to doubt. Doubt is not taking something for granted. Taking something for granted is to accept its truth value.

3. In order to doubt, in order to put something into question, we must take other things for granted.

4. It is therefore impossible to doubt everything at the same time.

5. Descartes doesn’t realize (3) and so makes the mistake of jumping from a specific doubt to general doubt.

That, in a nutshell, is the first mistake. You say I’ve missed Descartes’s point but I’m not attempting to describe the point, I’m attempting to attack the idea that we can doubt everything at the same time. I think that if we accept this, his solution to the problem of doubt falls apart.

His quest for certainty is misguided because the very ability to doubt presupposes certainty in other areas. It was already there. If you question the accuracy of your senses you already presuppose that you have senses in order for the question to make sense.

Now, this type of certainty apparently doesn’t satisfy Descartes, he wants to find something that can’t be doubted at all, that you can’t put into question (You’re right to say he needs God to do this.). His solution is that you can’t doubt the ability to doubt and still doubt. I argue that you can’t have the ability to doubt without already being certain of many, many things. Simply put, he hasn’t interrogated doubt enough and, as a result, privileges thoughts and the mind (that’s another mistake), the ghost in the machine, over and above the ‘external’ world. But he can’t privilege this ghost without contriving a rather arbitrary dividing line between the external and internal world. He simply avoids that

Donald Davidson, “The Myth of the Subjective”

That is, the only way he can privilege thoughts and doubt is by not asking where these things come from. If you have to be able to think in order to doubt, you have to be able to see in order to doubt what you see. Or to put it another way: rationality comes from somewhere, it is not a gift from God.

I’ll try to get more specific later but if you have time, I’d like to hear your arguments against Cartesian dualism.

He doesn’t doubt everything; but doubts the sources used in the acquisition of knowledge. As I’ve posted before:

“You must examine all human knowledge and see if it can be doubted. If it is dubitable and so ‘infected’, then it must be mercilessly rejected as flawed. I asked myself where all human knowledge comes from. I decided there are only two sources of knowledge: our sense and our reason.”

This is where he starts his sceptic journey. It just so happens none of these source can be found to be indubitable, so for a sceptic all is doubtable until he realises that he must have a consciousness to observe his own doubting, this he can’t doubt.

This isn’t exactly what Descartes says or does. An example: Imagine a river flowing down the side of a mountain and on it’s journey it passes through 4 villages. The 1st is closest to the rivers source, and the 4th closest to the sea. Now if the first 3 villages use this river to bath in, by the time it gets to the 4th the water could be quite dirty. The first village gets clean water, the second is slightly dirty, the third is more dirty, and then finally the fourth the waters dirty. If the 4th village wants clean water it must get it between the source and before the first village, because beyond that point it becomes contaminated. Now if somebody wanted to poison everybody in all of the 4 villages all they would need to do is go to the river’s source and mix in the poison there. The flow of the river would then automatically poison everybody and everything a long it’s path.

This is the same for the two sources of knowledge that Descartes believes all knowledge stems from. If the source itself is contaminated with doubt, this doubt will be passed onto all knowledge that springs from it. I hopefully explain this clearly in my post about “questioning opinions”

The part in bold is not true, yes he accepts that he has senses, but not that they are true or that they are real, only that it appears he has them. The only certainty is that he is thinking about this problem, but for everything else, there is no certainty, as when he sleeps these senses give him very different pictures of the world, which we call dreams. How do we know we’re not in some dream like state right now? Most people have at one time in their life woken up in a cold sweat from a nightmare that they believed to be true, up until the point of waking that is. How do I know I’m not going to wake up before I finish reading this post?

Even the most simplistic of animal brains have the ability to doubt. I would also speculate that doubt would be one of the first “conscious” brain functions acquired. Why? Because of the ‘Fight or Flight’ response. To make the decision to Flight or run away is to doubt that you can Fight and win. All animals have this ability; all animals are capable of doubt even if they don’t have beliefs or a historical context. It’s much more basic then that. Yes he’s right they do shape them, but that view is more of an anthropologists view then a philosophical one.

I have cover indirectly in my other reply to you on “questioning opinions”. If you would like a fuller account let me know and I’d be more the happy to type it up.

Definitely got some good stuff here and in the other thread. Let me try to address three points here:

First,

Now, I’ve taken the Davidsonian route here, but you can also take the Wittgensteinian route and question the connection between dubtibility and knowledge. I’ll let that go for now, but I want to point out that this quote already presupposes his conclusion. Why did he decide that there are only two sources of knowledge? Why lump all five sense together and call it sense, why separate this from thinking processes? Why, in fact, call these sources, even separate sources, of human knowledge and not facets of a holistic human individual? Senses and reason aren’t sources of knowledge, they are what make us us. Do you see how the conclusion is foretold by the premises inherent in this quote?

It may seem like I’m being a little hard on the old French guy here, but that’s not really my intention. I think these basic Cartesian intuitions are still the default position for many, and while I probably won’t be able to persuade many people that there’s a better way to go, I might be able to modify this dualism just a bit and, as I said before, show that we aren’t cut off from the world at all. Of course, I suppose I haven’t done a very good job at doing that yet.

I’ll address your river source point later, but I see no inherent reason to confine ourselves to two abstract sources of knowledge and many good reasons to see many ways of checking and double checking what you call sources. To go back to the stick for example, how does Descartes know that his senses are deceiving him if he didn’t, I don’t know, thrust his hand in the water and find his sight misleading him. It seems very clear to me at any rate that he just could have accepted that something about the distinction between water and air changes the nature of the stick rather than the nature of his sight. Now, you’ll probably say that he doesn’t know that he’s being deceived, he’s only stating the possibility of being deceived – two different things – but my point would be that he knows that he can possibly be deceived. If he doesn’t work from that point, I don’t see how he can get any further than an endless, circular doubt.

Second, the dream hypothesis.

Ironically, those who propound this theory never seem to take it seriously enough. When you’ve been dreaming, most of the time you know your dreaming, but I accept the idea of lucid dreaming – a point for whatever reason where you really can’t tell the difference. I’ve been in one of those dreams where you wake up in the dream and given that it was a RipVanWinkel kind of dream, it was a rather frightening and dismaying experience. Yet, nevertheless, most of my beliefs remained intact, it was not a completely alien world, my wife was twenty years older but she looked the same (and she blamed me for sleeping for twenty years just as she blames me for many things I consider out of my control ), my daughter kept flashing between my picture of her now and my picture as she might be twenty years from now (much like it might happen if it, well, really happened). The point is that if this is a dream right now, it doesn’t change the fact that even in dreams most of your beliefs aren’t questioned. If they were, dreams wouldn’t be interpretable (both in and outside of the dream) and of course they are.

We might even say that the only thing being put into question is the dream/reality distinction. To which my answer is so what? I see nothing foundational to that distinction. That shouldn’t be surprising as I don’t see any particular belief as foundational, I see them as holistically coping with the world. Descartes search for a foundation is flawed because the very search for a foundation seems to me to be flawed, even incoherent when we try to assess the things we actually do to get around in this world.

Less than a hundred years ago we believed in a steady state universe, fifty years ago, we believed in an expanding but slowing universe, we now believe, or many do at least, believe in an expanding but accelerating universe. Is that really any more fantastic than the idea that we live in a dream?

And anyway, last time I checked reason doesn’t account for such things as quantum superpositioning or tunneling.

Third, Matrix.

Enjoyable movie with its flaws and religious overtones (Who exactly is the Oracle anyway?). Look forward to the sequels. But my argument remains much the same. Given the premise that we could be in a computer simulation doesn’t change the fact that most of Neo’s beliefs are still true, it is only the way he received them that is different. They speak English in and out of the Matrix, he has people to help him through the transition, people who are much like the people he met in the Matrix, he still has to eat, he can still fall in love, and perhaps most poignantly for any kind of narrative tension, if you die in the Matrix, you die in the real world.

It really isn’t as staggering as some may think. The effect isn’t a representation of Cartesian thinking so much as caused by Cartesian thinking. If I remember my Celtic mythology/literature class correctly, the idea of other worlds was more or less taken as a given. So a Celt would simply see this as a jump to a different world.

And wonder of wonders, I think it’s clear that Neo already knew something was ‘not right’ with the world. He actually suspected it, and I suppose that many who take this movie more seriously than I do also have that feeling. Contrary to incoherence or destabilization, they might actually feel slightly vindicated. But that just means that one of my beliefs was false, and one of theirs was true. But most of our beliefs in either world are still true.

A far scarier proposition is something like Putnam’s second Twin Earth paradox. There’s a twin earth on the other side of the sun, in all respects the same as this one with one difference suitably adjusted for. Water on this planet is always twenty percent grain alcohol. This doesn’t bother them as their body chemistries are different enough to account for that (and let’s say their science gives them no ability to tell the difference between our water and their water). You are spirited away without your knowledge to this planet and find you are always drunk. At what point, do you stop arguing with other people that they are wrong and start questioning your own sanity?

Most of your beliefs are still true, but you have no way to account for this, not because you are wrong, not because they are wrong, but because you have no way to explain the difference between you and them.

What kind of hell would that be?

Therefore, the demon simply cannot trick me about everything at the same time.

Why not?
After all, even if I do have to accept some propositions as true in order to reject others as false, as you claim, why can’t it turn out that even the propositions I accept as true are, in fact, false. To accept some propositions as true doesn’t imply that they are true.

Furthermore, whatever propositions I accept as true, if the demon makes me believe (as he is supposed to have done) that there is a material world, and if there isn’t a material world, why hasn’t he “tricked me about everything at the same time?” What has to be true (and not only accepted as true) so that the world is not an illusion? It is true that the notion of illusion has to be contrasted with the notion of what is real. But it does not follow that there actually has to be anything real.
To make an analogy. Could all money be counterfeit money? Why not? It may be that we have to accept some money as genuine to reject some money as counterfeit, but it doesn’t follow that the money we accept as genuine is genuine. And it may be that the notion of counterfeit money has to contrast with the concept of genuine money. But it does not follow that there actually has to be genuine money for there to be counterfeit money.

But this is just to place emphasis on the real/illusion distinction, to make it a foundation. Assume everything is an illusion and you’ve really only changed one belief, cats are still cats, hammers still hammers etc… They just are now in a different overall framework. Not too long ago many people thought the Earth was flat or that we were carried by elephants. People accepted the change pretty quickly, but they didn’t plow or measure their fields any differently.

Other than reversing Ryle here, it’s hard for me to understand this. Money is a mind dependent concept. If, I don’t know, the mafia suddenly were able to replace genuine money with counterfeit, I suppose we could be fooled by this, but not without genuine money existing at some point. If money began as counterfeit money, then that would be genuine money or perhaps, more correctly, it’s simply incoherent to say something like that.

My problem begins with your view that what is accepted as true (by everyone? Who?) is, ipso facto, true. To talk about a proposition being “accepted” as true surely leaves room for its not being true. If I accept money as genuine, that still leaves room for its not being genuine.
I never used the word “illusion”. “Illusion” is an internal notion. And of course, cats are cats, and hammers are hammers. But that is only a tautology. But, if, hammers and cats are made up of space time points, they are, of course, still cats and hammers, but wildly different from how they appear to be. After all, even if they are "illusions’ they are not hallucinations.

As for genuine money. Genuine money is money produced by and certified by the United States. Now, there could have been a vast conspiracy whereby none of the money we take as money is genuine money. Think of it this way: is Confederate currency real currency? It was produced by the Confederacy, and accepted by people in the South as currency. But is was illegal all the same. Had the colonists lost the war against England, the Continental currency accepted and used in trade would not, well, be worth a continental.

Yeah, I realized what you were shooting for yesterday, tried to post an addition and it didn’t go through (Ah, these things happen.). If I’m right, you accept that we have to believe most of our beliefs our true but that that, by itself, doesn’t mean that they are true. The way we know that they are true is through a process Davidson calls triangulaton (Yep, he means it in the same way we use triangulation when on the high seas before GPS). Because we can be wrong about any one belief we are one point in a triangle with other minds and the external world as the other two. That we can actually be wrong about something presupposes that we can be right and triangulation is the trick that gets us there. For example, we (wife and I) recently watched the movie ‘Dinosaur’ with my daughter. She saw a dinosaur and said the Korean word for horse. We corrected her (though I don’t think it was such a bad categorization), but she wouldn’t have corrected herself if only herself existed, and we wouldn’t have known how to correct her without an external point that we all see.

Ironically, it’s our ability to doubt (more correctly, to be wrong) that gives us the vehicle to know we’re in the real world.

I like that last sentence (illusions but not hallucinations), but I still detect a kind of foundationalist residualism here. I see no reason to choose between different points of view (Is a coin really a circle if looked at a certain way or is it a thick line if looked at another way?). Cats and hammers are wildly different if looked at in different ways but that in no way puts the fact that you know what I’m talking about in question. We can describe them chemically, atomically, aurally, or visually. I see no reason to privilege one over the other.

And that ain’t going to change if we are wrong about what exactly reality is.

I think, as did Wilfrid Sellars, that the “scientific image” of the world is the authoritative description. The “manifest image” is the way, given who we are, we have to see the world, and it enables us to get along in the world (obviously, else we wouldn’t be here.) But the scientific image tells us the truth about cats and hammers, and isn’t that what we are aiming for?

Brad said earlier:

1 and 2 are fine, but 3 is just plain wrong. You can question something without taking anything for granted. You are basing 3 on learning that what you beleived was wrong. If everything you knew might be wrong, it would be impossible to learn that everything you knew was wrong at the same time, but that does not mean that it is impossible for everything you know to actually all be wrong at once, without you knowing it was wrong.

kennethamy,

No doubt, there’s every reason to accept scientific description on any of a number of occasions, but I see no reason to accept it across the board. A variation on Putnam explains it well: you aren’t going to do very well in courting a young lady by explaining that she is really nothing more than a collection of sense data to you.

Or

“Di-hydrogen monoxide, di-hydogren monoxide everywhere and not a drop to drink”

Mentat Monkey,

I am attempting to describe the nature of doubt. It has nothing to do with whether something is actually true or false (that involves triangulation as explained later). One cannot question without first taking the ability to question for granted (Hell, even Descartes got that one right), but that one acceptance presupposes a lot of other things that you can’t question while you are questioning something else.

Just give me an example of what you mean by

And I’ll change my tune.

[quote=“Brad”]
kennethamy,

No doubt, there’s every reason to accept scientific description on any of a number of occasions, but I see no reason to accept it across the board. A variation on Putnam explains it well: you aren’t going to do very well in courting a young lady by explaining that she is really nothing more than a collection of sense data to you.

Or

“Di-hydrogen monoxide, di-hydogren monoxide everywhere and not a drop to drink”

Well, of course. And neither is it a mistake to talk about the setting sun despite the fact that we are all (I hope) copernicuns. As Berkeley said, “Speak with the vulgar, but think with the wise.”

How, can anything, let alone, everything, you know be wrong? If you know it, then you can’t be wrong. That is one of the differences between knowing and believing.

Of course, to take something for granted doesn’t mean you are right to take it for granted. You may take something for granted, and be wrong to do so. Alas!

Now, let’s take Descartes’ own doubt, that there is a material world “external” to the mind. That the world is a kind of hallucination caused by the Demon. I don’t see right now what I have to believe to have that doubt. I suppose I have to believe there are hallucinations, and there are doubts. But that doesn’t seem to me germane to the doubt about the world. Perhaps it will be said that to believe there are hallucinations I have to believe there are real things. I don’t see that. Perhaps I have to believe there might be real things, but that only means I have have to have the concept of a non-hallucination. Is that all there is to Brad’s claim?

I’m not sure if this will add anything to the discussion, but maybe Brad’s claim is similar to some medieval arguments concerning the nature of God, in that we can know through negation; and that having the ability to know that something is false in the world at least requires that you aren’t doubting that what you ‘know,’ is in fact false about the world? so in order to doubt, you at least have to assume that you can doubt?

But Brad, doesn’t any argument about how we know or about reality itself involve at least one presumption to base the argument upon? And can’t that in itself always be questioned?