What I said, or at least meant to say is that my certainty of whether or not there is "a green growing thing that I can see through my window", is dependent on the certainty that I have an unmistakably correct understanding of what that phrase means. If I cannot be certain that my understanding of the phrase is not mistaken, then I cannot be certain as to whether or not the phrase is true. And, the belief that the rules for understanding are like sign-posts, leaves me in the position where I cannot be certain that I am not misunderstanding the meaning of the phrase. Therefore I cannot be certain whether or not the phrase is true, and so I do not agree that there is no uncertainty.

What I said, or at least meant to say is that my certainty of whether or not there is "a green growing thing that I can see through my window", is dependent on the certainty that I have an unmistakably correct understanding of what that phrase means. — Metaphysician Undercover

Well happily, I can confirm that there is not "a green growing thing that I can see though my window" anywhere except on my computer screen. The only phrase I can see though my window is "Coastal Mobility" which is written on the building opposite. But since you are not sure that you understand what I am talking about, I might as well stop talking. When you say 'phrase', I assume you mean 'tasty sausage', is that right?

Philosophy treats "Misunderstandings concerning the use of words, caused, among other things, by certain analogies between the forms of expression in different regions of language." — Banno

For a curious example of analogies leading to misunderstanding, see @s's The mashed is the potato

When you say 'phrase', I assume you mean 'tasty sausage', is that right? — unenlightened

You've almost got it, but "phrase" is different from "tasty sausage", so that's not quite it. Every time someone says "phrase", they mean to say "phrase". But every time someone says "phrase", they might not be using the word in the same way as another time. So how can you be certain of how the person is using "phrase" at any particular time? Look at Wittgenstein's example of "Moses".

When you say 'almost' you mean 'exactly'. Oh but wait, I mean baked beans, you can't know yourself that you mean 'exactly', because you don't know that 'exactly' means 'what unenlightened meant', not to be confused with 'what unenlightened said', which is just a bunch of words that don't mean anything.

But don't worry, I am certain even if you don't know what I mean. But you can't be certain that I almost got it, unless you know what I meant by what I said, and that it almost meant 'it' where it means what you said., or what you meant by what you said, whatever that was - nobody knows.

Have to confess I struggled to misunderstand that - something about the Irish, an Orange parade and mashing people ... sounded a bit racist.

The appropriate way for Wittgenstein to deal with the infinite regress of explanation which is required to remove the possibility of misunderstanding, is to accept the fact that doubt cannot be excluded. This simply means that we proceed in our activities without certainty. And, this thing which he attempts to do, establish the foundations for an epistemology in which doubt has been removed, and there is certainty, is impossible. — Metaphysician Undercover

Wittgenstein in no way attempts to "establish the foundations for an epistemology in which doubt has been removed". This type of foundational philosophical thinking is rejected by Wittgenstein, and is a way of thought he is attempting to subvert via his therapeutic writing. The next 40-50 passages in the text seek to disabuse the reader of thinking in these ideal terms. Most of us - philosophers and non-philosophers alike - proceed in many of our daily activities with certainty without the need for any perfect epistemological foundation.

Wittgenstein repeats his "view" at §87:

...an explanation may indeed rest on another one that has been given, but none stands in need of another - unless we require it to avoid a misunderstanding. One might say: an explanation serves to remove or to prevent a misunderstanding —– one, that is, that would arise if not for the explanation, but not every misunderstanding that I can imagine. — PI 87

You could claim that Wittgenstein's therapeutic method has not worked for you and that you still crave the removal of every imaginable doubt. That's fine, but don't misread Wittgenstein to be providing a foundational philosophy which will help you with this.

For a curious example of analogies leading to misunderstanding, see s's The mashed is the potato. — Banno

Are you suggesting that they lead me to misunderstanding or others: those I'm critical of there? And what's this supposed misunderstanding?

Reply in messages.

Wittgenstein in no way attempts to "establish the foundations for an epistemology in which doubt has been removed". This type of foundational philosophical thinking is rejected by Wittgenstein, and is a way of thought he is attempting to subvert via his therapeutic writing. The next 40-50 passages in the text seek to disabuse the reader of thinking in these ideal terms. Most of us - philosophers and non-philosophers alike - proceed in many of our daily activities with certainty without the need for any perfect epistemological foundation. — Luke

I suggest you reread 85-87. It is all philosophical thinking, regardless of whether Wittgenstein says otherwise.

85: "the sign-post does after all leave no room for doubt. Or rather: it sometimes leaves room for doubt and sometimes not. And now this is no longer a philosophical proposition, but an empirical one."

The proposition that a sign-post sometimes leaves no room for doubt is not an empirical proposition, it's a philosophical proposition. The degree of doubt which an individual has, cannot be observed. empirically. And, the fact that an individual will proceed into an activity does not mean that the person does not have doubt concerning the success or failure of the activity. We often proceed into actions with doubt concerning the action's success. So we cannot use the empirical observation that the person is proceeding to act, to conclude that there is no doubt. This is a philosophical proposition made by Wittgenstein.

Further, the entirety of 87, discussing the need for explanation to avoid misunderstanding, along with the conclusion, "The sign-post is in order—if, under normal circumstances, it fulfils its purpose." is philosophical, and not empirical. The status of one's understanding, like the status of one's doubt cannot be empirically observed. And the judgement of whether something fulfils a purpose is not an empirical judgement because a purpose cannot be observed empirically, to determine whether the thing has fulfilled that purpose. So this quoted statement is clearly a philosophical proposition rather than empirical.

Therefore, if Wittgenstein proceeds to reject such philosophical thinking, then that is just more evidence of the incoherency of his position. The means by which he attempts to exclude doubt, is a philosophical argument, and a defective one at that. He really should not have ventured into that philosophical issue, and completely left aside the subject of doubt. It clearly is a philosophical subject, rather than an empirical subject, and his attempt to make it empirical is a failure. That his intent, in venturing into the subject of doubt, was to establish a foundation for an epistemology, is evident in On Certainty.

Most of us - philosophers and non-philosophers alike - proceed in many of our daily activities with certainty without the need for any perfect epistemological foundation. — Luke

I agree with this, many people, myself included, often claim to be certain. That is our habitual way of talking which is derived from our background of platonic idealism. Platonic idealism provides the grounds for certainty, in independent Forms, and it is the principal ontology of Christianity so it is bedrock in our linguistic habits. The point is that if we adhere to Wittgenstein's principles, that rules are sign-posts, we ought to recognize that these claims of certainty are unjustifiable. This leaves us with two options, either we accept that we ought not claim certainty, because such claims are false under our ontological principles, or we reject Wittgenstein's principles, which may allow us to find a way to justify our claims of certainty in another form of ontology. The problem is in trying to maintain both, our claims of certainty, and W's ontology of rules, because they are inconsistent with each other.

Reply in messages. — Banno

No, certainly not. If you're going to publicly use what I said in my discussion, in this discussion, as an example of an alleged misunderstanding, then I'm going to publicly defend what I said there over here. At least unless you delete your comment here.

PI points out how taking one way of using words and applying it in another situation leads to misunderstanding.

Your thread is an excellent example, in that you are misled by an analogy with things - oranges and potatoes - into treating meaning as if it were also a thing.

It isn't. But you showed Wittgenstein's point so clearly, I had to make use of it. — Banno

The irony is that the misunderstanding is your own.

First of all, let's be clear that it is not the case universally or in general that taking one way of using words and applying it in another situation leads to misunderstanding. But I don't doubt that it can, and that it does in some cases.

Second, my intention was not to suggest that meaning was a thing in the way that a potato is a thing. That's not the fault of my analogy, it's the fault of your misreading of it. My analogy was about the logical structure of the language. It was about a distinction between, say, an egg and a boiled egg. This can be expressed in predicate logic as P(x) and P(x, y).

The analogies just showed this in a more relatable way, with the use of familiar things, like potatoes and oranges, rather than jumping straight into a more abstract way of making the point. Clearly, you missed the point by a country mile, and naively thought that you could make an example of me here, and perhaps you even convinced yourself that I would let you get away with it.

It is all philosophical thinking, regardless of whether Wittgenstein says otherwise. — Metaphysician Undercover

I didn't say it wasn't philosophical thinking; I said it wasn't foundational philosophical thinking. See Foundationalism.

I'm not going to argue with you about whether to accept Platonic idealism, or whether to follow Wittgenstein in his rejection of this sort of foundationalism. But, of course, you should follow Wittgenstein. :grin:

I didn't say it wasn't philosophical thinking; I said it wasn't foundational philosophical thinking. See Foundationalism. — Luke

In relation to what is said at 87, this statement is questionable.

But, of course, you should follow Wittgenstein. :grin: — Luke

I agree, but despite his claims that doubt can sometimes be excluded, he hasn't shown me any principles whereby we can actually expect to exclude doubt in relation to any of our knowledge. So his position, even though he may have claimed otherwise, seems to be very supportive of skepticism.

In relation to what is said at 87, this statement is questionable. — Metaphysician Undercover

How so?

That's a better analysis. Cheers.

To remove doubt, we seek an explanation. But then the explanation requires an explanation, and unless it's the final one, it's as if the explanation is hung in the air. Wittgenstein prevents this possibility of infinite regress of doubt and explanation, by asserting that an explanation is only needed, "if required to prevent a misunderstanding".

That is the point I've been arguing. Notice that "to prevent a misunderstanding" implies that an explanation is needed any time misunderstanding is possible. If we cannot remove the possibility of misunderstanding, then an explanation is required. The nature of the rules for understanding, as Wittgenstein describes them as sign-posts, is such that there is always the possibility of misunderstanding the rule. That's the nature of a sign-post, as W describes. Therefore it appears like an explanation is required for everything, if we are to prevent the possibility of misunderstanding. Wittgenstein recognizes this problem in the following statement:

It may easily look as if every doubt merely revealed an existing gap
in the foundations; so that secure understanding is only possible if we
first doubt everything that can be doubted, and then remove all these
doubts. — 87

So he offers as a resolution, to eliminate that doubt, and secure the foundation, "The sign-post is in order—if, under normal circumstances, it fulfils its purpose." But this principle is completely impotent. for its intended purpose,

understand all this as saying that logic does not set out the rules of language, but that rather we choose a logic that suits what we are doing with language. — Banno

You don't mean that we literally choose a logic, do you? I think you mean it's as if we make a choice, because we think and speak and write in a way that is not fundamentally bound to any logic.

See

We choose a logic in the same way we choose the places of the pieces in a game of chess. We're not locked in. We might decide to play Chess960. Logic is about the rules of the game, but they are not crystalline.

But then the explanation requires an explanation, — Metaphysician Undercover

No, it doesn't.

...any time misunderstanding is possible — Metaphysician Undercover

You added the word possible.

Following the rule, or not, is shown in the doing. If the actions are in accord with the rules, that will suffice; if the signpost leads us in the right direction, that is all that we require of it. There is no need to dig further; but moreover, digging further would be an error.

Damn, I didn't want to get drawn in to this.

@Metaphysician Undercover, it's as if you were asking why the bishop only move diagonally, and wanting not an explanation from the history of the game, but a further rule within the game.

To those who accept the discussion made in PI, it's an absurd thing to do.

Again I'd suggest moving on, since there is no further way to convince Meta that it's a rabbit and a duck if he only sees the duck. The point must be taken as moot. As the conversation moves on, other points of disagreement will arise.

Damn, I didn't want to get drawn in to this. — Banno

Hi Banno, I welcome your contribution to this little problem which seems to be mine only. Getting bored elsewhere?

You added the word possible. — Banno

Right, that's the point. To prevent misunderstanding, requires having measures in place to prevent it, every time misunderstanding is possible. This is implied by "prevent misunderstanding". If you wait until after misunderstanding occurs, and try to fix it at that time, then you haven't prevented misunderstanding. Wittgenstein seems to be trying to dodge this fact.

Following the rule, or not, is shown in the doing. If the actions are in accord with the rules, that will suffice; if the signpost leads us in the right direction, that is all that we require of it. There is no need to dig further; but moreover, digging further would be an error. — Banno

I agree, if by "right direction" you mean as Wittgenstein says, the sign-post (rule) fulfils its purpose. If it fulfils its purpose it has lead you in the right direction. However, the possibility that it will be misunderstood is very real, and that's when explanation is necessary.

Wittgenstein could have stopped there, accepting that the possibility of misunderstanding is very real. If epistemologists said to him, you have a problem because doubt arises from the possibility of misunderstanding, he could have just replied that doubt is a fact of life, if that's a problem for your epistemology, then deal with it. Thus he might provide us with some grounds for skepticism. However, Wittgenstein did not stop there. He seems to have become obsessed with the idea that doubt is some sort of problem, and proceeded in On Certainty, in an attempt to limit doubt in some foundationalist way. But why? If his description of rules is accurate, and the result is that propositions of doubt and skepticism are valid propositions, then so be it.

it's as if you were asking why the bishop only move diagonally, and wanting not an explanation from the history of the game, but a further rule within the game. — Banno

I don't see what you are saying. The rule is the sign-post. I see a sign-post, (rule) and I'm not certain that I understand what it is telling me. If I need other sign-posts to understand that sign-post, then the probability of misunderstanding likely increases. Also, infinite regress is possible. My best option might be to proceed in the direction that I think the sign-post is telling me, but without certainty, with some degree of doubt.

Again I'd suggest moving on, since there is no further way to convince Meta that it's a rabbit and a duck if he only sees the duck. The point must be taken as moot. As the conversation moves on, other points of disagreement will arise. — Banno

I think you have the roles reversed. I see the rabbit and the duck, skepticism and foundationalism. The problem is that to assume both is incoherent. If the sign-post (rule) is designed such that it will tell you both "I'm a duck", and "I'm a rabbit", then it's not a sign-post (rule) at all, because it's designed to confuse you. And when the purpose is to confuse you, we call that deception. We ought not allow so-called sign-posts, whose purpose is to deceive, fulfil their purpose.

To remove doubt, we seek an explanation. But then the explanation requires an explanation, and unless it's the final one, it's as if the explanation is hung in the air. Wittgenstein prevents this possibility of infinite regress of doubt and explanation, by asserting that an explanation is only needed, "if required to prevent a misunderstanding". — Metaphysician Undercover

The Wikipedia article defines Foundationalism thus: "Foundationalism is an attempt to respond to the regress problem of justification in epistemology. According to this argument, every proposition requires justification to support it, but any justification also needs to be justified itself. If this goes on ad infinitum, it is not clear how anything in the chain could be justified. Foundationalism holds that there are 'basic beliefs' which serve as foundations to anchor the rest of our beliefs."

The basic beliefs of foundationalism are the "final" explanations to which Wittgenstein refers here:

But similar doubts to those about the name “Moses” are possible about the words of this explanation (what are you calling “Egypt”, whom the “Israelites”, and so forth?). These questions would not even come to an end when we got down to words like “red”, “dark”, “sweet”. - “But then how does an explanation help me to understand, if, after all, it is not the final one? In that case the explanation is never completed; so I still don’t understand what he means, and never shall!” - As though an explanation, as it were, hung in the air unless supported by another one. — PI 87

Wittgenstein's solution is to provide a circuit breaker to the regress. We don't need to justify every word or statement, as the regress problem would have it; we only need to provide an explanation in order to avoid a misunderstanding. Wittgenstein cuts off the regress near the surface level of language use, rather than at the foundation.

Whereas an explanation may indeed rest on another one that has been given, but none stands in need of another - unless we require it to avoid a misunderstanding. One might say: an explanation serves to remove or to prevent a misunderstanding —– one, that is, that would arise if not for the explanation, but not every misunderstanding that I can imagine. — PI 87

It is hard to see why you think that this is a foundationalist philosophy. There is no chain of justification ending at basic beliefs here: "none stands in need of another - unless we require it to avoid a misunderstanding".

You provided a quote from the end of §87:

It may easily look as if every doubt merely revealed a gap in the foundations; so that secure understanding is possible only if we first doubt everything that can be doubted, and then remove all these doubts. — PI 87

Yes, it may easily look like that, HOWEVER....

The signpost is in order - if, under normal circumstances, it fulfils its purpose. — PI 87

That is, the signpost is in order if, under normal circumstances, no further explanation is required to avoid a misunderstanding. Conversely, we avoid a misunderstanding if, under normal circumstances, the signpost (or words used) fulfils its purpose.

it's as if you were asking why the bishop only move diagonally, and wanting not an explanation from the history of the game, but a further rule within the game.
— Banno

I don't see what you are saying. — Metaphysician Undercover

Indeed.

Wittgenstein's solution is to provide a circuit breaker to the regress. We don't need to justify every word or statement, as the regress problem would have it; we only need to provide an explanation in order to avoid a misunderstanding. Wittgenstein cuts off the regress near the surface level of language use, rather than at the foundation. — Luke

If these sign-posts (rules) do not need further explanation, then they are foundational. You are simply calling them "surface level". Anyway, whether it's properly called foundational or surface level is irrelevant, the point is that whatever you call it, it doesn't succeed as an attempt to justify certainty.

It is hard to see why you think that this is a foundationalist philosophy. There is no chain of justification ending at basic beliefs here: "none stands in need of another - unless we require it to avoid a misunderstanding". — Luke

There is a problem of infinite regress of explanation described by Wittgenstein at 87. Unless it is the "final" explanation, it is as if the explanation is just hanging in the air. He makes "an attempt to respond to the regress problem", as per your definition of foundationalism. The "none stands in need of another
- unless we require it to avoid a misunderstanding", represents that attempt. Call it surface level rather than foundational if you want.

The problem, as I just explained to Banno, is that to avoid misunderstanding requires that we eliminate the possibility of misunderstanding. (In On Certainty he describes objectively certain as logically excluding the possibility of mistake). Remember, what Wittgenstein is trying to curb is doubt, and doubt is induced by the possibility of misunderstanding. But, due to the nature of rules, having the characteristics of sign-posts, there is always a possibility of misunderstanding. Therefore an explanation would always be required to avoid the doubt incurred by the possibility of misunderstanding. So, Wittgenstein's attempt to avoid the infinite regress fails.

That is, the signpost is in order if, under normal circumstances, no further explanation is required to avoid a misunderstanding. Conversely, we avoid a misunderstanding if, under normal circumstances, the signpost (or words used) fulfils its purpose. — Luke

Right, I took this up with unenlightened already. How would one determine "normal circumstances" to know whether an explanation is required or not, to avoid misunderstanding. Further, how would you know whether or not the sign-post fulfilled its purpose, and avoided misunderstanding until after it is too late to avoid misunderstanding. This principle is completely impotent as an attempt at indicating when an explanation is or is not required. It amounts to stating "If there was normal circumstances, and the sign-post fulfilled its purpose, then misunderstanding was avoided". It tells us nothing about how to know when misunderstanding is probable, and therefore an explanation is required.

Indeed. — Banno

Misunderstanding, therefore explanation was required.

You simply repeat the interlocutor's concern at §87: "But then how does an explanation help me to understand, if, after all, it is not the final one? In that case the explanation is never completed; so I still don’t understand what he means, and never shall!”

Yet you fail to acknowledge or be satisfied by Wittgenstein's response.

I have no further interest in attempting to explain it.

You simply repeat the interlocutor's concern at §87: "But then how does an explanation help me to understand, if, after all, it is not the final one? In that case the explanation is never completed; so I still don’t understand what he means, and never shall!”

Yet you fail to acknowledge or be satisfied by Wittgenstein's response.

I have no further interest in attempting to explain it. — Luke

Yes. The so-called interlocutor's concern is a concern which Wittgenstein had about his description of rules, or else he would not have brought it up as a concern. And, as I've explained, Wittgenstein's response to that concern is lame. It's inconsistent with his description. He may have been better off not to have broached the issue of doubt. It's an issue he was not prepared to deal with.

...there is always a possibility of misunderstanding. Therefore an explanation would always be required to avoid the doubt incurred by the possibility of misunderstanding. So, Wittgenstein's attempt to avoid the infinite regress fails. — Metaphysician Undercover

You complain that doubt can always remain; that we can always fall short of an exact understanding, but these are merely imagined possibilities. The logical result of this claim is that understanding (or exact understanding) is impossible.

Can you honestly state that there has never been an occasion on which you have understood a signpost or what someone tells you? Understanding signposts and what people say is both possible and actual - it happens every day.

So, what do you mean by exact understanding?

No single ideal of exactness has been envisaged; we do not know what we are to make of this idea - unless you yourself stipulate what is to be so called. But you’ll find it difficult to make such a stipulation - one that satisfies you. — PI 88

You complain that doubt can always remain; that we can always fall short of an exact understanding, but these are merely imagined possibilities. The logical result of this claim is that understanding (or exact understanding) is impossible. — Luke

They are not imagined possibilities, they are what Wittgenstein describes. I believe what he describes, but if you think his description is imaginary, that's between you and him. Look at how he describes exactness at 88. The degree of exactness which we strive for, which is required, is relative to our purpose, the goal, what we are doing (his example of time is very good).

I think we should have the same attitude with respect to misunderstanding, and doubt. We should limit the possibility of misunderstanding (this is doubt, recognition of the possibility of misunderstanding), to the degree required for our purposes. Wittgenstein is rejecting the notion that we strive for "ideals". But if he posits "certainty', or "leaves no room for doubt", as what he is striving for, he is just being hypocritical. In this case he has made his goal an ideal, an absolute, and this is inconsistent with the way that he says we use words. We do not strive for ideals, we settle for what is required relative to the purpose at hand.

The "logical result", of "misunderstanding is possible" is not "understanding is impossible", and I don't know what you would mean by "exact understanding". The point is that we ought to limit the possibility of misunderstanding to a degree acceptable, relative to the situation. If the president of the USA has his finger on the nuclear button, there is a need to limit the possibility of misunderstanding to a high degree. When my wife gives me a list of items for the grocery store, I need to limit the possibility of misunderstanding to a lesser degree. But striving for certainty, in the sense of leaving no room for doubt, is nonsense in the context of PI. To strive for the ideal would actually defeat the purpose of the book.

Can you honestly state that there has never been an occasion on which you have understood a signpost or what someone tells you? Understanding signposts and what people say is both possible and actual - it happens every day. — Luke

This is judgement after the fact, it's irrelevant. What we are talking about is avoiding misunderstanding, preventing misunderstanding. We are talking about a judgement made by the person planting the sign-posts, prior to the act of reading the sign-posts. But I'll tell you one thing, the fact that understanding is possible, does not produce the logical conclusion that misunderstanding is impossible. You seem to be employing some bad logic.

Yes. The so-called interlocutor's concern is a concern which Wittgenstein had about his description of rules, or else he would not have brought it up as a concern. — Metaphysician Undercover

This is a continuation of the problem he addresses in 81:

All this, however, can appear in the right light only when one has attained greater clarity about the concepts of understanding, meaning something, and thinking. For it will then also become clear what may mislead us (and did mislead me) into thinking that if anyone utters a sentence and means or understands it, he is thereby operating a calculus according to definite rules.

We do not need or employ a calculus according to definite rules in order to use language. We do not have to remove all doubt in order to understand.

The question in 87:

“But then how does an explanation help me to understand, if, after all, it is not the final one? In that case the explanation is never completed; so I still don’t understand what he means, and never shall!”

The questioner is misled into thinking that if anyone utters a sentence and means or understands it, he is thereby operating a calculus according to definite rules. Wittgenstein himself was misled in this way. In the Tractatus he assumed that language was built on names of simple objects and that underlying them was logic, that is, the rules by which objects are connected and propositions operate. It was an image of perfect clarity. But it was wrong.

Language does not require perfect clarity. It is not built on a fixed structure of logic or rules. Misunderstanding is always possible, but this does not mean that understanding is impossible. When misunderstanding arises we attempt to correct it by an explanation. That explanation too might be misunderstood. But this does not mean that an explanation that leads to understanding is not possible. We cannot, however, eliminate the possibility of misunderstanding. No matter how precise the language, no matter how hard one attempts to anticipate where someone might misunderstand what is said, there will be someone who does misunderstand it. This is simply the way things are.

I'm with you there. Now the question I've been asking is why does Wittgenstein appear to persist in this misguided objective, to find the principles which exclude the possibility of misunderstanding, in On Certainty? And even here, at 85, where he says that the sign-post "sometimes leaves room for doubt and sometimes not"? If he has determined here, that there are no such principles of certainty, no such logic which excludes the possibility of misunderstanding, underlying our language and knowledge, and that it was misguided or wrong to have assumed such, then why does he proceed in that text, On Certainty, as if he is seeking these principles? Do I completely misunderstand his intention in On Certainty, is he trying to give "certainty" a different meaning which does not consist of excluding the possibility of mistake? Or does he misunderstand the principles he has stated here, himself?

The point being that if there is a possibility of misunderstanding, then some degree of doubt is justified. Therefore doubt cannot be completely dismissed as irrational. But Wittgenstein appears to have a desire to completely dismiss doubt in some situations, as completely irrational in those situations, without completely excluding the possibility of misunderstanding in those situations, and this itself is irrational.

There is a kind of foundationalism in On Certainty, but it's not traditional foundationalism. It's a foundationalism driven by language-games and context. So, if we were to look at chess as an example, the rules, the board, and the pieces are foundational to the game. One doesn't need to justify the rules, no more than one needs to justify the statement "This is my hand," it's just part of the background in which we act. There are many foundational statements in our language. One can generally spot them because knowing and doubting are for the most part senseless in relation to these kinds of bedrock statements.

Is Wittgenstein putting forth a theory of foundationalism, of course not, but it seems to follow from many of his thoughts. Many philosophers have interpreted Wittgenstein in this way, but they're careful about how they frame the idea. There is no doubt, at least as I interpret Wittgenstein, that Moore's statements
do fall into a kind of foundational thinking. Whether a statement is foundational depends on the context, and in Moore's context, viz, "This is my hand," it is foundational.