Except I don't imagine ghosts to be electromagnetic radiation. I imagine them to be non-physical things. — Michael

No you don't. This is what you imagine:



How are ghosts shown in paintings, etc. ? Be honest with yourself. You can't imagine a non-physical thing. What you really mean by non-physical in this context is something that has a shape, but can go through walls, etc. that kinda stuff.

How are ghosts shown in paintings, etc. ? Be honest with yourself. You can't imagine a non-physical thing. What you really mean by non-physical in this context is something that has a shape, but can go through walls, etc. that kinda stuff. — Agustino

So all you're saying is that my concept of a ghost can only include visual qualities that I've experienced in real life (forgetting the other senses for the sake of argument)?

Then for this to work for your argument it must be that being of an external world is a visual quality that I've experienced in real life. Except being of an external world isn't a visual quality at all (not a shape or a colour or anything like that). In fact, the very concept of being of an external world is tied to the notion of there being something which transcends the experience. So if I can only conceive of a thing if I've seen it then to conceive of a thing that exists when not being seen I must have seen a thing that isn't being seen? That's obviously nonsense. Furthermore, your argument entails that there is some visual (or other qualitative) feature that external world experiences have and other experiences don't. What is that feature?

But the concept of an external world doesn't come from experience at all, but from rational consideration. We have experiences, and then imagine something like the things we experience happening even when we're not around.

The concept of an external world doesn't come from experience at all, but from rational consideration. — Michael

Yes it does. You experience things like your thoughts and emotions, and you see that they're not always the same. But you wake up in the same bed (presumably). Because of its constancy, you deem one to be independent of your experience - it looks the same every time you come back to it - while the other - like dreaming, your mind, etc. you view it as depending on your experience. This concept arises precisely out of experience - more specifically the experience of the constancy of the external world, and the impossibility of altering it just by thinking about it. That's why you call it external in the first place.

Yes it does. You experience things like your thoughts and emotions, and you see that they're not always the same. But you wake up in the same bed (presumably). Because of its constancy, you deem one to be independent of your experience - it looks the same every time you come back to it - while the other - like dreaming, your mind, etc. you view it as depending on your experience. This concept arises precisely out of experience - more specifically the experience of the constancy of the external world, and the impossibility of altering it just by thinking about it. — Agustino

That's not experiencing an external world. That's using rational consideration to try to explain the consistency of experiences.

A brain in a vat would also come to the same conclusion to explain the consistency of his experiences, despite the fact that none of his experiences are of an external world.

But simply having a veridical experience isn't evidence that it's a veridical experience, just as simply having the real painting isn't evidence that it's the real painting. — Michael

But this analogy doesn't work. If you are in a waking state your experience is strongly correlated with how things are in your environment (otherwise it would not be a waking experience by definition), and hence it is correct to regard your perceptual states as good evidence. But in the case of paintings, unless you are an expert, nothing in your experience is correlated with the fact whether the painting is genuine or not, and so your experience shouldn't be considered as evidence in favor of either possibility.

The trick here is in treating "waking experience" and "dreaming experience" as two different kinds of state, and this distinction is epistemically relevant because having a waking experience is by its very nature to perceive reliably how things are in the world, which is not the case with dreams.

The evidence must allow you to rule out the possibility that you're wrong, and for that you need to recognise some distinguishing feature, as with the painting. — Michael

The question here is which possibilities do we have to rule out. Suppose that in the case of the paintings, I can detect the "distinguishing features" of some forgeries, but not others which are more sophisticated. Does the fact that I cannot rule out more sophisticated forgeries somehow undermines my ability to detect the less sophisticated ones? Surely not (at least in the sense of that I can know when something is a forgery if it is not very sophisticated). So I grant you that we cannot distinguish all conceivable cases of perceptual error (such as in the radical skeptical scenarios), but we do have the capacity to rule out some cases of error. And after all, the skeptic doesn't claim that we cannot e.g. distinguish dogs from cats in normal lighting conditions etc., he's having in mind much more exotic cases. And thus the idea is that the inability to distinguish some hypothetical cases of dreaming from waking, doesn't prove that we can never distinguish dreaming from waking, since in a straightforward sense we often can do just that.

Now if having a waking experience defined as a state such that things necessarily match the way they appear to me, then if I'm having a waking experience I'm in a state which entails the presence of whatever that I perceive — Fafner

But how do you know how things are? You can't know that, you can only ever know how they appear to you. Same question here:

The trick here is in treating "waking experience" and "dreaming experience" as two different kinds of state, and this distinction is epistemically relevant because having a waking experience is by its very nature to perceive reliably how things are in the world, which is not the case with dreams. — Fafner

Your arguments seem to be built around the premise that you have an external and reliable source of information of how things really are, that you can compare your perceptions to.

There's no reason to assume that whenever I know something, then I must be able to recognize all possible cases of deception or illusion. — Fafner

How so? If you are not, then it's possible that case of deception or illusion is true, and so you can't be sure things are how you think they're instead of you being deceived, ie. you don't know for sure.

A brain in a vat would also come to the same conclusion to explain the consistency of his experiences, despite the fact that none of his experiences are of an external world. — Michael

Sure, but the brain in the vat has no grounds to doubt that his experience is of an external world (and in some sense it is, because the electrical impulses stimulating his brain do come from an external world).

That doesn't mean that the scenario isn't logically possible, but something being logically possible is not sufficient to form a ground for doubting it.

If you are in a waking state your experience is strongly correlated with how things are in your environment (otherwise it would not be a waking experience by definition), and hence it is correct to regard your perceptual states as good evidence. — Fafner

You have to look at this from the perspective of the person under consideration. He can only treat his experiences as being good evidence that his experiences are veridical if he has good evidence that his experiences are veridical, which of course is circular.

Your argument is akin to saying that if I have an accurate report of some event then it is strongly correlated with how things happened, and so it is good evidence that the report is accurate. But it doesn't work that way.

Simply having an accurate report isn't evidence that the report is accurate, and simply having veridical experiences isn't evidence that the experiences are veridical.

And thus the idea is that the inability to distinguish some hypothetical cases of dreaming from waking, doesn't prove that we can never distinguish dreaming from waking, since in a straightforward sense we often can do just that.

This is why the terms "waking" and "dreaming" are such bad terms to use. It can lead to equivocation, as I tried to explain here. On the one hand we might want to define the terms according to whether the experiences are of an external or imaginary world, and on the other hand we might want to define the terms according to their ordinary referents. Compare with the case of atoms and the definition of "atom" as "indivisible".

Far better to just stick with "experience of an external world" and "experience of an imaginary world". So the sceptical hypothesis is that we can't (or just don't) know if our experiences are of an external world or an imaginary world, and more strongly that the experiences that we ordinarily consider to be of an external world are actually of an imaginary world.

So even though we can distinguish between two types of experience – the one which we call "being awake" and the one which we call "dreaming" – both of these are actually of an imaginary world. They just differ in quality, with the former being far more vivid and consistent.

But how do you know how things are? You can't know that, you can only ever know how they appear to you. — BlueBanana

Well, if you have evidence that entails that things are the way the they seem, then I think it's very plausible to call it knowledge.

How so? If you are not, then it's possible that case of deception or illusion is true, and so you can't be sure things are how you think they're instead of you being deceived, ie. you don't know for sure. — BlueBanana

But what if cases of illusion or deception are not actually possible, given the state the I'm right now in? (i.e., of not dreaming but being awake) Maybe if I were dreaming, then I couldn't recognize that I'm dreaming, but what are the odds the I'm really dreaming right now? Surely my not being able to recognize all cases of dreaming, don't prove that I'm actually dreaming right now! So you have to distinguish between subjective and objective reasons, so to speak.

Sure, but the brain in the vat has no grounds to doubt that his experience is of an external world (and in some sense it is, because the electrical impulses stimulating his brain do come from an external world). — Agustino

That the experience is caused by an external world is not that it is of that external world, else all dreams would also be of an external world (and so I guess I could turn your argument around on you and claim that you've destroyed the meaning of "dreaming").

And the sceptic isn't saying that we have a good reason to believe that our experiences are of an imaginary world. He's just saying that we can't (or don't) know that they aren't.

He's just saying that we can't (or don't) know that it isn't. — Michael

Knowledge is that which we have when we don't have grounds for doubt. Knowledge can change and evolve.

Knowledge is that which we have when we don't have grounds for doubt. Knowledge can change and evolve. — Agustino

So you equate knowledge with certainty (in the sense of conviction). The sceptic doesn't, and neither do most philosophers. I might not have any grounds to doubt my girlfriend's faithfulness, but that doesn't mean that I know she hasn't cheated on me.

So you equate knowledge with certainty (in the sense of conviction). — Michael

No, quite the contrary, the skeptic sets the bar for knowledge too high. He says knowledge only exists in the complete impossibility of doubt. And then he bases his doubt off logical possibility which is irrational.

Knowledge just requires the elimination of real - not imaginary - doubt.

I might not have any grounds to doubt my girlfriend's faithfulness, but that doesn't mean that I know she hasn't cheated on me. — Michael

Yes it does. Until further evidence, you know she hasn't cheated on you. You cannot rationally doubt her faithfulness if you have no reason to.

Yes it does. Until further evidence, you know she hasn't cheated on you. You cannot rationally doubt her faithfulness if you have no reason to. — Agustino

For one, I can only know that she hasn't cheated on me if she hasn't cheated on me. Knowledge requires truth, not just no reason to doubt. But then as Gettier showed, truth and justification are not sufficient either.

For one, I can only know that she hasn't cheated on me if she hasn't cheated on me. Knowledge requires truth, not just no reason to doubt. But then as Gettier showed, truth and justification are not sufficient either. — Michael

I can't agree with that, because what we mean by truth is most often approximation. At least in most contexts we use it in.

Well, if you have evidence that entails that things are the way the they seem, then I think it's very plausible to call it knowledge. — Fafner

First, what even is this evidence you could have of things being as they seem? Second, knowledge in this context means 100% certain with absolutely no possibility of it being false in any hypothetical or theoretical situations, no matter how inplausible. So no, unless you can distinguish any deception or illusion, the claim is not palusible.

But what if cases of illusion or deception are not actually possible, given the state the I'm right now in? (i.e., of not dreaming but being awake) — Fafner

This seems like circular reasoning. You're awake because there can't be the illusion of you being asleep because you'd know it because you're awake.

Surely my not being able to recognize all cases of dreaming, don't prove that I'm actually dreaming right now! — Fafner

No, but that's not the point. It proves that it's a possibility, even if the odds of that are one in infinity, and that there's no absolute proof of you being awake.

Simply having an accurate report isn't evidence that the report is accurate, and simply having veridical experiences isn't evidence that the experiences are veridical. — Michael

Well yes, having an accurate report doesn't prove by itself that your report is accurate, but having an accurate report is having good evidence for the thing which is reported (you've just called it "a good report" after all). And from the fact that you don't have some independent checks for the reliability of your report it doesn't follow that it is epistemically imprudent or irresponsible to rely on a report which looks to be a reliable report as far as one can tell. And so if it is indeed a good report then it seems to me reasonable to describe this as a case of genuine knowledge of the thing which is reported.

Far better to just stick with "experience of an external world" and "experience of an imaginary world". So the sceptical hypothesis is that we can't (or just don't) know if our experiences are of an external world or an imaginary world, and more strongly that the experiences that we ordinarily consider to be of an external world are actually of an imaginary world. — Michael

I think that actually your terminology is way more confusing then mine, but I won't argue about that. I just wanted to show that there's a natural understanding of "evidence" (and in particular the evidence provided by perceptual experience), on which all this talk about distinguishing between dreaming and reality is irrelevant to our actual state of knowledge of the world. And so there's really no good reason to think that our inability to detect some crazy possibilities of dreams should undermine our confidence in sense experience.

All that the skeptic can tell us is that either our experience is wildly misleading in a very systematic way because of some ad hoc coincidence, or that it is very reliable as we usually take it to be. But it should be noted that the skeptical scenario is in some sense 'parasitic' on the intelligibility of the ordinary scenario that we normally believe in (since it is essentially defined by contrasting it with the normal case); and so if those are our only two choices (and there's really nothing in between), then it is not clear why there should be even a prima facie reason to think that the skeptical scenario is even remotely relevant to our ability to know the world.

Well yes, having an accurate report doesn't prove by itself that your report is accurate — Fafner

So having a veridical experience doesn't prove that the experience is veridical. And the sceptic's claim is that we can't know that our experiences are veridical.

And from the fact that you don't have some independent checks for the reliability of your report it doesn't follow that it is epistemically imprudent or irresponsible to rely on a report which looks to be a reliable report as far as one can tell

So in this case we have some means to test the accuracy of the report. We can check to see if things are as the report says. But what can we do to test the veridicality of an experience? How do we check to see if our experiences correspond to some external world? This is where we need to be able to recognise some feature that veridical experiences have and non-veridical experiences don't.

The fundamental problem with the notion of an external world experience is that it places the very thing that defines it as being an external world experience outside the experience. The brain in a vat has no way of knowing if his simulated world is an accurate representation of the external world.

First, what even is this evidence you could have of things being as they seem? Second, knowledge in this context means 100% certain with absolutely no possibility of it being false in any hypothetical or theoretical situations, no matter how inplausible. So no, unless you can distinguish any deception or illusion, the claim is not palusible. — BlueBanana

It all depends on what one calls "evidence" here. My proposal is to distinguish between having evidence for something (which is an objective matter of how your mental state is connected with the real world), and being able to subjectively detect various cases of error, which is something else. And I think that once you have this distinction clearly in mind, the skeptics' argument loses much of its plausibility. The skeptic after all doesn't really challenge the actual reliability or veridicality of your perceptual states (= the evidence available to you), but he's just changing the subject by talking about remote possibilities of error, which don't really undermine the objective evidential status of your experience, but merely challenge your entitlement to rely on them. But then why should one really care about some imagined scenarios of deceiving demons etc.? After all, the skeptic doesn't even claim that the possibility that you are dreaming is remotely plausible, but only that it is "possible" in some abstract sense, and therefore it seems to me that we can safely ignore this possibility.

No, but that's not the point. It proves that it's a possibility, even if the odds of that are one in infinity, and that there's no absolute proof of you being awake. — BlueBanana

Yes, but the question is how the absence of such proof is relevant to my knowledge of the world.

So having a veridical experience doesn't prove that the experience is veridical. And the sceptic's claim is that we can't know that our experiences are veridical. — Michael

The skeptic can claim this, but as I said many times, it doesn't follow from this that we cannot know anything about the external world.

So in this case we have some means to test the accuracy of the report. We can check to see if things are as the report says. But what can we do to test the veridicality of an experience? How do we check to see if our experiences correspond to some external world? This is where we need to be able to recognise some feature that veridical experiences have and non-veridical experiences don't. — Michael

As I said, in most cases it is pretty simple thing to do. If you want to make sure that what you are seeing is a cat and not e.g a rock or a dog, you can approach it and examine it more closely and so on. So there are actually many distinguishing features by which we can ordinarily tell whether an experience corresponds to the world or not (and they are not arbitrary) - but of course such tests are not infallible and don't rule out all possible cases of error, but the point is - so what? Relying on perceptual experience is not simply a matter of making guesses (as you claimed) because we do have all sorts of reasonable standards for determining whether an experience warrants a certain belief, and so there's something very weird in the skeptics' claim that all those standards are completely worthless unless we can first of all rule out a possibility of some sort of crazy error. Surely the relevant question to ask whether I know that something is a cat is whether what I see appears as a cat - and the question whether I'm dreaming or something like that, has nothing to do with it and hence simply irrelevant.

The fundamental problem with the notion of an external world experience is that it places the very thing that defines it as being an external world experience outside the experience. The brain in a vat has no way of knowing if his simulated world is an accurate representation of the external world. — Michael

I don't agree that the external world is "outside" our experience. And surely you have to know first whether there is actually an external world, in order to know whether it is outside our experience, don't you think?

I don't agree that the external world is "outside" our experience. — Fafner

In that case, you might say why you're *not* idealist.

The skeptic can claim this, but as I said many times, it doesn't follow from this that we cannot know anything about the external world. — Fafner

You've phrased this very ambiguously. Let's say I meet a woman and that, unbeknown to me, she's your mother. In one sense it is correct to say that I know your mother, but in another sense it's wrong to say that I know that she's your mother.

The sceptic is saying something about the latter sort of knowledge. I can't know that the experience I'm having is an experience of an external world.

Surely the relevant question to ask whether I know that something is a cat is whether what I see appears as a cat - and the question whether I'm dreaming or something like that, has nothing to do with it.

It has everything to do with that. The sceptical hypothesis is that we can't know that we're not brains in a vat, for example. No amount of examining cats is going to help us answer that. Unless there's some known testable feature that "real" cats have and simulated cats don't.

I don't agree that the external world is "outside" our experience. And surely you have to know first whether there is actually an external world, in order to know whether it is outside our experience, don't you think?

I think that's just true by definition. We say that some object is "external" if it exists when not being experienced. How do I check to see that the cat I see exists when not being experienced? I can't. That's where scepticism comes in.

You've phrased this very ambiguously. Let's say I meet a woman and that, unbeknown to me, she's your mother. In one sense it is correct to say that I know your mother, but in another sense it's wrong to say that I know that she's your mother.

The sceptic is saying something about the latter sort of knowledge. I can't know that the experience I'm having is an experience of an external world. — Michael

We've been over this already. There's no much that I can add.

It has everything to do with that. The sceptical hypothesis is that we can't know that we're not brains in a vat, for example. No amount of examining cats is going to help us answer that. Unless there's some known feature that "real" cats have and simulated cats don't. — Michael

Again, you are just assuming here that knowing that p requires the ability to detect every conceivable possibility of p being false, while I saying that such an assumption is unwarranted. Again, there's no much that I can add to what I already said on this point.

I think that's just true by definition. We say that some object is "external" if it exists when not being experienced. — Michael

But when you actually do experience the object, then it is not "outside" you experience in the sense that the object doesn't make any difference to how things appear to you, since it surely does (- if this is what you meant to deny in your last comment).

Again, you are just assuming here that knowing that p requires the ability to detect every conceivable possibility of p being false, while I saying that such an assumption is unwarranted. Again, there's no much that I can add to what I already said on this point. — Fafner

How can you claim that knowing that p consists of anything other than excluding the possibility that p is false? If you can know that p, without excluding the possibility that p is false, then what does "knowing that" amount to?

How can you claim that knowing that p consists of anything other than excluding the possibility that p is false? If you can know that p, without excluding the possibility that p is false, then what does "knowing that" amount to? — Metaphysician Undercover

I didn't actually deny what you said that I denied (that knowing p means ruling out p's falsehood) - and I agree with you on this. I only disputed the claim that knowing must also entail being able to detect (from the subjects point of view) all cases of p's falsehood, which is something else.

What must rule out the possibility of falsehood is your objective evidence. So for example, if you are in a waking state perceiving a tree in full daylight, you cannot possibly be in this very same state and still be wrong about the tree. But what you can be in error about is whether you are really in such a state or merely seeming to be; so it might seem to you that you are looking at a tree in a waking state, when you are actually asleep, or something like that.

So my point is this - when you know that p, then your evidence must objectively entail the truth of p - but this is compatible with your subjective inability to detect all instances of p's falsehood (but you should be able to detect at least some of them, but not the ones that the skeptic says that you should - e.g., you would notice if someone cut down the tree for example, but not if you were a brain in the vat in a treeless world etc.).

So my point is this - when you know that p, then your evidence must objectively entail the truth of p — Fafner

It's not enough that the evidence objectively entails the truth of p. If I meet your mother and if she has blond hair then the evidence objectively entails that your mother has blond hair, but unless I know that she's your mother it would be wrong to say that I know that your mother has blond hair.

And so if I see an external world tree then the evidence objectively entails that there is an external world tree, but unless I know that it's an external world tree it would be wrong to say that I know that there's an external world tree.

Your argument seems to conflate on "objectively ruling out the possibility of falsehood". What matters for knowledge is that I can recgonise the evidence as objectively ruling out the possibility of falsehood. Your approach seems to just be the truism that if the belief is true then it cannot be false.

I didn't actually deny what you said that I denied (that knowing p means ruling out p's falsehood) - and I agree with you on this. I only disputed the claim that knowing must also entail being able to detect (from the subjects point of view) all cases of p's falsehood, and I think this is something else. — Fafner

I assume you mean all possible instances of p's falsehood. Without detecting, and negating all possibility of p's falsehood, you retain the possibility that p is false. So you seem to be saying that you allow for the undetected possibility that p is false, when you know that p.

What must rule out the possibility of falsehood is your objective evidence. So for example, if you are in a waking state perceiving a tree in full daylight, you cannot possibly be in this very same state and still be wrong about the tree. — Fafner

I don't see how you can make this conclusion. A person in a waking state may have poor eyes, poor judgement, or be hallucinating when thinking that they are in a state of perceiving a tree. You seem to be neglecting the fact that evidence must be judged. The person must judge the perceptual evidence, as well as the meaning of the statement "that is a tree", in order to know that that is a tree. Human judgements can be mistaken. Therefore the person can be wrong.

So my point is this - when you know that p, then your evidence must objectively entail the truth of p - — Fafner

So here you use "objectively entail" to refer to the judgement which must be made. How do you ensure that the human judgement is not mistaken?

Your approach seems to just be the truism that if the belief is true then it cannot be false. — Michael

But that's not what I'm saying. Compare the case of believing that there's a tree outside because you seem to see that there's a tree outside, and just guessing correctly that there's a tree outside. In the first case you are basing your belief on a capacity that within certain parameters (that is, in the right sort of environment) is an extremely reliable tree-detector (meaning it can detect real trees as opposed to fake trees, but not real trees as opposed to extremely vivid hallucinations). While in the second case of guessing you are not exercising any such a capacity, but merely depending on pure chance. But if you are exercising your tree detecting capacity in the right sort of environment, then it's not a matter of chance that you seem to see a tree whenever there are real trees (and not seeing trees when they are none), so there's an important difference between relying on perceptual experience, and merely guessing correctly.

But that's not what I'm saying. Compare the case of believing that there's a tree outside because you seem to see that there's a tree outside, and just guessing correctly that there's a tree outside. In the first case you are basing your belief on a capacity that within certain parameters (that is, in the right sort of environment) is an extremely reliable tree-detector (meaning it can detect real trees as opposed to fake trees, but not real trees as opposed to extremely vivid hallucinations). While in the second case of guessing you are not exercising any such a capacity, but merely depending on pure chance. But if you are exercising your tree detecting capacity in the right sort of environment, then it's not a matter of chance that you seem to see a tree whenever there are real trees (and not seeing trees when they are none), so there's an important difference between relying on perceptual experience, and merely guessing correctly — Fafner

In my example I see your blond mother, but I still don't know that your mother is blond. It's not enough that I exercise a reliable detecting capacity in the right sort of environment. I need periphery understanding (in this case, that the person I see is your mother).

In my example I see your blond mother, but I still don't know that your mother is blond. It's not enough that I exercise a reliable detecting capacity in the right sort of environment. I need periphery understanding (in this case, that the person I see is your mother). — Michael

I didn't say that having this sort of capacity is sufficient for knowledge, that's a different question. Obviously you have to be responsive in the right sort of way to the deliverances of you perception - I agree that not all instances of e.g. directly seeing a tree (de re) are instances of knowledge, but I don't see the relevancy here.