"Here is a hand" is true IFF here is a hand. What more empirical a demonstration could there be than Moore waving his hand at you? — Banno

OC 3:
If e.g. someone says "I don't know if there's a hand here" he might be told "Look closer". - This
possibility of satisfying oneself is part of the language-game. Is one of its essential features.

It does not go any deeper than looking and seeing.

I think Wittgenstein is being playful: "look closer". The problem is not with what is seen, it is with thinking there is good reason to doubt it.

The skeptic has it backwards, believing that reason is the ground and arbiter; that in order to know that there is a hand here we must satisfy the doubts raised by reason.

When someone looks at a post-box and says "I know the post-box is red", what they really mean is that when looking at the post-box they have the sense impression red.

If they had said "I know when looking at the post-box my sense impression is red because the post-box is emitting light at a wavelength of 750nm", it is true that they don't need a reason to justify that they know their own sense impression.

If they had said "I know that the actual post-box is red, not just my sense-impression", the sceptic is justified to ask them for what reason they think they know that the actual post-box is red. If they cannot give a suitable reason, then the sceptic had justification to ask.

When someone says that they know something about which they have no direct knowledge,
the sceptic is justified in asking for a reason.

When someone looks at a post-box and says "I know the post-box is red", what they really mean is that when looking at the post-box they have the sense impression red. — RussellA

Speaking as someone, that is not at all what I mean. What I really mean is that I am able to distinguish between post-boxes that are red and post-boxes that are not.

What do you really mean when you say you have the sense impression red? How do you know it is red? Do you compare it to a red post-box? Does your sense impression emit light at a wavelength of 750nm?

When someone says that they know something about which they have no direct knowledge, the sceptic is justified in asking for a reason. — RussellA

What serves as direct knowledge that a post-box is red? A sense impression? That may be direct knowledge of the sense impression but the sense impression is not the post-box. Only the post-box can serve as the source of direct knowledge of the color of the post-box.

What serves as direct knowledge that a post-box is red? — Fooloso4

Light having a wavelength of 750nm travels the 10m from the post-box to our brain through our eyes.

There is no information within light having a wavelength of 750nm that is able to determine that the observer will have the sense impression of red, rather than green, say. For example, one person may see red and another person may see green.

Therefore, the colour an observer sees is a function of the observer and not of the light travelling from the object.

Therefore, it is not that the actual post-box is red, but rather we observe the post-box as being red.

Therefore, the colour an observer sees is a function of the observer and not of the light travelling from the object. — RussellA

What color is the mailbox in the dark?

For example, one person may see red and another person may see green. — RussellA

Does this mean that if I them to paint the box red one will do so correctly and the other will paint it green? Or is there no correct here?

Does this mean that if I them to paint the box red one will do so correctly and the other will paint it green? — Fooloso4

No - they will both paint it red.

No - they will both paint it red. — RussellA

But you previously said:

When someone looks at a post-box and says "I know the post-box is red", what they really mean is that when looking at the post-box they have the sense impression red. — RussellA

and then:

For example, one person may see red and another person may see green.

Therefore, the colour an observer sees is a function of the observer and not of the light travelling from the object.

Therefore, it is not that the actual post-box is red, but rather we observe the post-box as being red. — RussellA

So, the person sees green yet knows that the post-box is red despite his sense impression not because of it.

Now it may be that she has learned that her sense impression for green is what other people call red. The problem is she is still able to distinguish between green and red post-boxes. If someone painted the box green would she see it as green or red or some other color? In any case, she is able to make a distinction and that distinction must have something to do with the color of the post-box.

You also said:

Therefore, the colour an observer sees is a function of the observer and not of the light travelling from the object. — RussellA

In the dark we cannot observe the color. Isn't this because what the observer sees has something to do with the light travelling from the object?

Are you claiming to be unable to distinguish a hand waved by Shrek from one waived by Moore?

Elsewhere, you appear to move between belief and knowledge with blithe disregard for their differences. One's belief may be false, not so one's knowedge.

One's belief may be false, not so one's knowedge. — Banno

Especially if it's carnal knowledge.

So, the person sees green yet knows that the post-box is red despite his sense impression not because of it. — Fooloso4

A person can know several different things at the same time.

The person can know that the publicly accepted word for the colour of the post-box is "red" - though it could have been "rouge" or "rot".

The person can also know their own conscious experience of a particular colour.

There is no way of knowing whether one person's conscious experience of the wavelength 750nm is the same as anyone else's. It could be that two people have the same conscious experience of 750nm - let us call it red. It could be that that one person's conscious experience of 750nm - let us call it red - is different to someone else's conscious experience of 750nm - let us call it green.

IE, a person could know two things. First, that the external public name of the colour of the post-box is "red" and second, that their internal private conscious experience of 750nm is green.

Are you claiming to be unable to distinguish a hand waved by Shrek from one waived by Moore? — Banno

Whilst watching TV, I see a figure waving a hand. As the figure has a green face, I know it is more likely to be Shrek than Moore.

However, the sceptic would be justified in pointing out that my TV is old and tends to give a green tinge to everything, and ask my reasons why I think it is Shrek rather than Moore.

IE, I can distinguish between Shrek and Moore, but I may be wrong.

There is no way of knowing whether one person's conscious experience of the wavelength 750nm is the same as anyone else's. — RussellA

Yea there is. We can look at a particular part of the body and ask “Is this involved in the experience of color”. We can do experiments to determine whether it is or not. Take toe size. If toe size had anything to do with the experience you get when a 750 nm wavelength enters your eye, then you’d expect that a person with a swollen toe would report seeing different colors than usual. That isn’t the case so it’s not a significant variable.

Repeat this process, then eventually you will positively be able to answer whether or not someone’s conscious experience of 750 nm is the same as anyone else’s. If they have identical significant variables, they’re the same. Or at least, we’d be justified in believing they’re the same.

You previously said:

If they had said "I know that the actual post-box is red, not just my sense-impression", the sceptic is justified to ask them for what reason they think they know that the actual post-box is red. If they cannot give a suitable reason, then the sceptic had justification to ask. — RussellA

but now:

A person can know several different things at the same time.

The person can know that the publicly accepted word for the colour of the post-box is "red" - though it could have been "rouge" or "rot".

The person can also know their own conscious experience of a particular colour. — RussellA

So which is it? Does a person know it or is the skeptic justified in asking for the reason they think they know it?

So which is it? — Fooloso4

The problem with the English language is that many of its' words have several meanings, such as the word "know". Context does not always make it clear which meaning is intended. Life would a lot easier if each meaning of the word "know" had its own individual sub-word. Though that would meaning a lot more words.

eventually you will positively be able to answer whether or not someone’s conscious experience of 750 nm is the same as anyone else’s. — khaled

The enclosed article may do a better job of what I am trying to say.
https://www.uh.edu/engines/epi3161.htm

We are not talking about the various uses of the work 'know'. We are talking about skepticism. How is it that when:

The person can know that the publicly accepted word for the colour of the post-box is "red" - though it could have been "rouge" or "rot".

The person can also know their own conscious experience of a particular colour. — RussellA

the skeptic is still justified in asking for the reason they know it? If the person is able to distinguish between a red post-box and a green post-box or for that matter a red post-box and an aardvark then what is missing from their knowledge that justifies doubting it?

One's belief may be false, not so one's knowledge. — Banno

Introduction
The truth of the statement "One's belief may be false, not so one's knowledge" depends on the meaning of "knowledge". The nature of knowledge has been discussed since at least Plato, so I don't think I will be able to resolve the matter in this post.

Knowing and believing
I am trying to keep my use of the words "knowledge" and "belief" within a framework, whereby a sentient being pre-language knows internal consciousness , knows external observations and believes external possibilities. A sentient being with language knows internal consciousness, believes external observations and believes external possibilities.

One advantage of a sentient being with language only believing in external observations rather than knowing them is possibly an answer to Russell's problem of how to think about non-existent things - a problem approached by Wittgenstein in his Tractatus regarding possible worlds.

Different theories of knowledge
Whether knowledge can be false depends on the definition of knowledge, as there are different defintions as to what knowledge is.

For example, there is internal knowledge. There is knowledge of a skill or ability, such as "I know how to play football". There is knowledge of one's own consciousness, such as "I know pain"

There is external knowledge. There is knowledge by acquaintance, such as "I know there is a tree in the garden". There is knowledge by proposition, such as "I know the Eiffel Tower is in Paris".

I cannot doubt internal knowledge, but I can doubt external knowledge.

It is possible to have different types of knowledge at the same time. For example, when looking at a post-box, I know the proposition "red light has a wavelength of between 620nm and 750nm", I know that I am looking at a post-box and I know my conscious experience of a particular colour

Wittgenstein and knowing
Wittgenstein in On Certainty was concerned with excluding doubt in his refutation of scepticism - OC 341. "That is to say, the questions that we raise and our doubts depend on the fact that some propositions are exempt from doubt, are as it were like hinges on which those turn."

However, in order to exclue doubt, one must also exclude knowing - OC354 "Doubting and non-doubting behaviour. There is the first only if there is the second"

As Grayling wrote - i) "The well-known, and persuasive, central tenet of OC is its view that claims to knowledge only make sense where the possibility of doubt exists." - ii) "His contribution is to insist on the internal connection between the concepts of knowing and doubting. "

For this reason, Wittgenstein argued against Moore when Moore said "Here is one hand", "How absurd it would be to suggest that I did not know it, but only believed it, and that perhaps it was not the case!"

For Wittgenstein, the word "know" is only an assurance - OC21. Moore's view really comes down to this: the concept 'know' is analogous to the concepts 'believe', 'surmise', 'doubt', 'be convinced' in that the statement "I know..." can't be a mistake.

For Wittgenstein, Moore should have argued from "here is one hand" rather than "I know that here is one hand"

IE, For Wittgenstein, it is not the case that knowledge cannot be doubted, but that knowledge is only an assurance, and as such can be doubted.

Justified true belief
Since Plato, knowledge has been defined as justified true belief. If the three conditions of justification, truth and belief are met for a given claim, then we have knowledge of that claim.

However, in 1963 Gettier argued that, by giving counter-examples, whilst an individual can have a JTB, the individual may still fail to know it because the reasons for the belief, whilst justified, turn out to be false.

There are different solutions to the Gettier problem. Some look for a fourth condition, others look to replace "justification" with something else. As yet, no definitive solution has been agreed upon.

Summary
As some kinds of knowledge may be doubted, there remains an overlap between knowledge and belief, in that the statement "I know that the post-box is red" overlaps with the statement "I believe that the post-box is red"

what is missing from their knowledge that justifies doubting it? — Fooloso4

If someone says "I see a post-box, and it exists in a world external to me", the sceptic is justified in asking the speaker, first, how they know there is an external world, and second, how they know there is a post-box in this external world. What is missing from the speaker's knowledge is evidence for their belief.

What is missing from the speaker's knowledge is evidence for their belief. — RussellA

The evidence of their belief is the fact that they are able to distinguish a red post-box from all else.

But we are now just repeating ourselves.

I've replied to this so often that I use the reply for my Bio:

Statements are combinations of nouns and verbs and such like; Some statements are either true or false, and we can call these propositions. So, "The present king of France is bald" is a statement, but not a proposition.

Beliefs range over propositions. (arguably, they might be made to range over statements: Fred believes the present king of France is bald.)

Beliefs set out a relation of a particular sort between an agent and a proposition.

This relation is such that if the agent acts in some way then there is a belief and a desire that together are sufficient to explain the agent's action. Banno wants water; he believes he can pour a glass from the tap; so he goes to the tap to pour a glass of water.

The logical problem here, the philosophical interesting side issue, is that beliefs overdetermine our actions. There are other beliefs and desires that could explain my going to the tap.
______________

We know some statement when at the least we believe it, it fits in with our other beliefs, and when it is true.

The "fits in with other beliefs" is a first approximation for a justification. Something stronger is needed, but material implication will not do.

Discard Gettier. The definition is not hard-and-fast.

It does not make sense to ask if we know X to be true; that's exactly the same as asking if we know X. The "we only know it if it is true" bit is only there because we can't know things that are false.

If you cannot provide a justification, that is, if you cannot provide other beliefs with which a given statement coheres, then you cannot be said to know it.


A belief that is not subject to doubt is a certainty.

Without a difference between belief and truth, we can't be wrong; if we can't be wrong, we can't fix our mistakes; without being able to fix our mistakes, we can't make things better.

I note the use of internal and external in you examples. You have reinforced my suspicion about the distinction between subjective and objective views. It seems to confuse people dreadfully.

Just as shoes that are too tight make it difficult to walk, the language used by philosophers makes it difficult to think. — Fooloso4

:point:

Grayling reads philosophy back into the anti-philosophy. — Banno

:point:

How does Husserl's 'lifeworld' fit in here?

The term “lifeworld” thus denotes the way the members of one or more social groups (cultures, linguistic communities) use to structure the world into objects (Husserliana, vol. VI, pp. 126–138, 140–145). The respective lifeworld is claimed to “predelineate” a “world-horizon” of potential future experiences that are to be (more or less) expected for a given group member at a given time, under various conditions, where the resulting sequences of anticipated experiences can be looked upon as corresponding to different “possible worlds and environments” (Husserliana, vol. III/1, p. 100). These expectations follow typical patterns, as the lifeworld is fixed by a system of (first and foremost implicit) intersubjective standards, or conventions, that determine what counts as “normal” or “standard” observation under “normal” conditions (Husserliana, vol. XV, pp. 135 ff, 142) and thus as a source of epistemic justification. — SEP

https://plato.stanford.edu/entries/qm-copenhagen/

In whatever way we may be conscious of the world as universal horizon, as coherent universe of existing objects, we, each "I-the-man" and all of us together, belong to the world as living with one another in the world; and the world is our world, valid for our consciousness as existing precisely through this 'living together.' We, as living in wakeful world-consciousness, are constantly active on the basis of our passive having of the world... Obviously this is true not only for me, the individual ego; rather we, in living together, have the world pre-given in this together, belong, the world as world for all, pre-given with this ontic meaning... The we-subjectivity... [is] constantly functioning. — Husserl

https://en.wikipedia.org/wiki/Lifeworld

In my naive self-consciousness as a human being knowing himself to be living in the world, for whom the world is the totality of what for him is valid and existing, I am blind to the immense transcendental dimension of problems … I am completely … bound by interests and tasks … [and] a certain habitual one-sidedness of self interest … I can, however, carry out the transcendental re-orientation in which … I now have, as a new horizon of interest … a new, infinite scientific realm—if I engage in the appropriate systematic work …

One kind of thinking … tries to bring ‘original intuition’ to the fore—that is, the pre- and extrascientific lifeworld … The proper return to the naïveté of life—but in a reflection that rises above this naiveté—is the only way to overcome this … naiveté …

In science we measure the lifeworld … for a well-fitting garb of ideas … It is … a method which is designed for progressively improving … through ‘scientific’ predictions, those rough predictions which are the only ones that are possible within the sphere of what is actually experienced and experienceable in the lifeworld …

Considering ourselves … as scientists … the manner of scientific thinking puts questions and answers them theoretically in relation to the world … Cofunctioning here are the other scientists who, united with us in a community of theory, acquire and have the same truths or … are united with us in a critical transaction aimed at critical agreement …

For the human being in his surrounding world there are many types of praxis, and among them is this peculiar … one, theoretical praxis. It has its own professional methods; it is the art of … discovering and securing truths with a certain new ideal sense which is foreign to [extra]scientific life, the sense of a certain ‘final validity’ …

Thus, a new way of experiencing, of thinking, of theorizing, is opened … here, situated above his own natural being and above the natural world, the scientist or philosopher loses nothing of their being and objective truths and likewise nothing at all of the spiritual acquisitions of his world-life or those of … historical communal life … Yet, as a scientist or philosopher, I stand above the world, which has now become for me, in a quite peculiar sense, a phenomenon’ … — Husserl

https://newlearningonline.com/new-learning/chapter-7/husserl-on-the-task-of-science-in-and-of-the-lifeworld

@RussellA, looking back over your posts, it seems to me that you are looking at these arguments with only part of Wittgenstein's analysis of meaning to hand. Wittgenstein, along with other analytic philosophers, rejected the notion of fixed meanings. Instead of looking to meanings he exhorted philosopher to look to what is being done with the words. Much of what you have said stands; if anything, it's stronger to point to the use of a word changing from one instance to another than talikng of the meaning changing.

So to this:

My understanding of the meaning of the concept "house" is just that set of the simpler concepts it is composed of, eventually leading to what Kant called a priori pure intuitions, such as space, time, causation, green, etc. — RussellA

That looks very similar to the description of language found in his Tractatus. It's pretty much the notion Wittgenstein critiqued in his later work, Philosophical Investigations. One argument he offered, for example, was to question what it was to count as a simple; he pointed out that what counted as a simple in one situation might not be a simple in a different situation (around §48 in PI).

Just a few thoughts.

ife would a lot easier if each meaning of the word "know" had its own individual sub-word. Though that would meaning a lot more words. — RussellA

I think we'd need infinitely more words. Doesn't every speech act have a certain uniqueness? This quote seems relevant.

One important aspect of the difference between Quine’s and Wittgenstein’s conceptions of philosophy, is their opposite attitudes towards linguistic diversity. According to Wittgenstein, philosophical problems arise because we go astray in the ancient city of language. To find our way about, we have to remind ourselves of how the streets that we habitually walk every day actually look, and how they are connected to each other. Naturally, this will involve reminding ourselves of the more or less detailed differences between various buildings and blocks. Hiding or obliterating such differences only makes the necessary orientation more difficult, or even impossible. Indeed, it might have been precisely such obliteration which made us go astray in the first place. Being able to resist the inclination to impose uniformity on language is therefore, according to Wittgenstein, a central philosophical virtue.

Quine’s viewpoint is quite different. He wants philosophers to be like city-planners who replace old, irregular housing areas by new, uniform blocks. In a scientific spirit of systematicity and simplification, Quine thinks we should dispense with all “quirks of usage that we can straighten.” [Quine 1960:158] Allegedly, philosophers should not try to give a wholly faithful description of actual language use, but rather improve language by fitting it into an austere “canonical notation” that employs only the constructional resources of first-order predicate logic. [1960:226ff.] Only such “regimentation” - a process of “coax[ing]” and “trimming” that may even require “some torturing” - makes it possible to perform the supposedly necessary “clearing of ontological slums.” [1987:157; 1960:180, 275]
— link

http://web.abo.fi/fak/hf/filosofi/Research/Spraxis/DAVIDSON.HTM

If the entire system is intrinsically consistent, and valid, which it must be to be a "system", then no part of the system can be doubted without doubting the whole. — Metaphysician Undercover

What if the system is not perfect? In OC, Wittgenstein still treats humans being on the moon as an obvious absurdity. It seems to me that you are thinking of some philosophical system when the issue is rather what 'reasonable' people take for granted, some of which the 'reasonable' people of the future will find absurd or cruel.

208. I have a telephone conversation with New York. My friend tells me that his young trees have buds of such and such a kind. I am now convinced that his tree is... Am I also convinced that the earth exists?
209. The existence of the earth is rather part of the whole picture which forms the starting-point of belief for me.
210. Does my telephone call to New York strengthen my conviction that the earth exists?
Much seems to be fixed, and it is removed from the traffic. It is also so to speak shunted onto an unused siding.
211. Now it gives our way of looking at things, and our researches, their form. Perhaps it was once disputed. But perhaps, for unthinkable ages, it has belonged to the scaffolding of our thoughts.
(Every human being has parents.) — OC

When someone says that they know something about which they have no direct knowledge, sceptic is justified in asking for a reason. — RussellA

The sceptic here takes the ideas of 'direct knowledge' and 'justification' for granted. You mention 'sense data.' That's a philosophical idea. Typically people just see the red mailbox. For the skeptic to worry about the gap between color reports and what color is really there is already to take some theory of perception for granted.

In general, the idea is that intelligible doubt (as opposed to nail-biting paralysis) has a specificity that points to a context of some taken-for-granted framework.

One important aspect of the difference between Quine’s and Wittgenstein’s conceptions of philosophy, is their opposite attitudes towards linguistic diversity — link

When an author uses a critical word that they know can be interpreted in more than one way, then, as a general principle, they should somehow make it clear to the reader in what sense they are using it - unless they are a poet.

The sceptic here takes the ideas of 'direct knowledge' and 'justification' for granted. — j0e

Grayling points out the two types of scepticism: scepticism within the foundationalism of OC1 and scepticism within the relativism of OC2

What if the system is not perfect? — j0e

Perfection is a requirement of logic, that is how logic works. Following the rules to the degree of perfection is necessary. If you propose a part of a logical system which does not follow the rules of that system, we must exclude it as not being part of the system. Otherwise logic loses its effectiveness because invalidities are acceptable.

It seems to me that you are thinking of some philosophical system when the issue is rather what 'reasonable' people take for granted, some of which the 'reasonable' people of the future will find absurd or cruel. — j0e

I think reasonable people will see the need to have logic rule over any system of beliefs. If you are proposing that beliefs ought to be ruled by a system which is not a logical system, it is rather an imperfect system, then you rob yourself of the capacity to exclude doubt. The exclusion of doubt requires perfection in the logical system.

This is the point I made, which Banno scoffed at. Allowing that a system of beliefs may be imperfect means that the entire system needs to be subjected to doubt. This is proof that the idea of hinge propositions, which it is unreasonable to doubt, is fundamentally flawed.

If we make an analytical separation between the rules of the system (formal aspect), and the subject matter, and adhere to perfection in the rules, as the means to exclude doubt, then the subject matter, content becomes the source of mistake. Since the subject matter comes from outside the system and therefore has not been subjected to the rules of the system, doubting of the subject matter is a requirement, if certainty is the goal. The proposed hinge propositions are subject matter, content, and therefore need to be doubted, just like any other portion of the subject matter.

209. The existence of the earth is rather part of the whole picture which forms the starting-point of belief for me.

...

211. Now it gives our way of looking at things, and our researches, their form. Perhaps it was once disputed. But perhaps, for unthinkable ages, it has belonged to the scaffolding of our thoughts. — OC

Wittgenstein misuses the word "form" here. Such ideas like "the existence of the earth" do not form starting points, nor do they give our way of looking at things, a form. Form is principles of formulae, definition, logical rules, etc.. The "existence of the earth" is not such a principle, because "existence" is a complicated and very much disputed concept. That the earth must in some way "exist" comes about as a conclusion, as a requirement when we seek to justify other beliefs. And the way that we seek to justify these beliefs shapes the concept of "existence". That's why "existence" is a disputed and unclear concept. The basic beliefs roll around in people's heads, and off their tongues and pens, for many years as a the subject matter of thinking, with an inherent rule or form (such a bud belongs to a specific type of tree for example), without asking to be justified by "the existence of the earth".

But when we seek to extend the rules, the formal structures, uniting them such that all of our beliefs must maintain coherency within a single system, each itself justified by others, then we approach the need to conclude "the existence of the earth". But this idea, "the existence of the earth", does not give our way of looking at things their form, it is a conclusion derived from our way of looking at things, deemed as necessary to give that way of looking at things a place within a larger unity. The larger unity is an attempt at completion, logical perfection within the distinct belief systems. So it is derived from the form of our way of looking at things, it does not give our way of looking at things its form.