That's different.

My interpretation of OC comes closest to Danièle Moyal-Sharrock (University of Hertfordshire). I arrived at my interpretation quite independent of her or any other philosopher. My idea of pre-linguistic beliefs, which I've often compared with animal beliefs is similar to comments she made about the animal in OC (OC 359). I believe, as does she that Wittgenstein solves the infinite regress problem in epistemology, which is one of his contributions to the subject of epistemology. As she says, "it puts a logical stop to infinite regress."

"Wittgenstein's revolutionary insight in On Certainty is that what philosophers have
traditionally called 'basic beliefs' – those beliefs that all knowledge must ultimately be based
on – cannot, on pain of infinite regress, themselves be propositional beliefs. They are really
animal or unreflective ways of acting which, once formulated (e.g. by philosophers), look like
propositional beliefs. It is this misleading appearance that leads philosophers to believe that at
the foundation of thought is yet more thought. For, though they often resemble empirical
conclusions, basic certainties (or 'hinge certainties' or 'hinges' – as I shall also call them
following Wittgenstein's hinge metaphor [OC 341]) constitute the ungrounded,
nonpropositional underpinning of knowledge, not its object. In thus situating the foundation
of knowledge in nonreflective certainties that manifest themselves as ways of acting,
Wittgenstein has found the place where justification comes to an end, and solved the regress
problem of basic beliefs – and, in passing, shown the logical impossibility of radical or global
scepticism. I believe that this is a groundbreaking achievement for philosophy – worthy of
calling On Certainty Wittgenstein's 'third masterpiece' (The Animal in Epistemology:
Wittgenstein's Enactivist Solution to the Problem of Regress, by Daniele Moyal-Sharrock)."

What may count as good reasons for you may not be what others regard as good reasons. Once again: — Fooloso4

Well, I don't view good reasons as something subjective, as if it's just some decision I make arbitrarily.

336. But what men consider reasonable or unreasonable alters. At certain periods men find
reasonable what at other periods they found unreasonable. And vice-versa.
But is there no objective character here?
Very intelligent and well-educated people believe in the story of creation in the Bible, while others
hold it as proven false, and the grounds of the latter are well known to the former.

Unpacking this can be tedious, but I don't think there is any problem here. I'm not talking in absolute terms but in general terms. You seem to be pushing Witt into a more relativistic position, but I don't. There is a relativistic point to all this of course, but there is also an objective component, which is more important.

If I had to characterize “hinge proposition” I would say it is one where a human accepts it and its logical consequences as a whole. This acceptance would not be because it strikes us as true but that it has some pragmatic effect on us that when we put them into practice it brings value and meaning to our lives. — Richard B

I'm not sure that we have the same view on hinge beliefs. It depends on what you mean by "logical consequences" of a hinge belief. There is no doubt that hinge beliefs have consequences in our acts (linguistic and non-linguistic), and that there is a logical scaffolding to our belief systems. However, we have different views of hinges if you use "logical consequences" as a synonym for correct reasoning (inductive and deductive). Also, hinge beliefs don't depend on some practical effect. A practical effect would give some justification for the belief, which goes counter what a hinge belief is.

Some may have as part of their hinge beliefs that sacrificing a child will yield more crops. So, are hinge beliefs relative to some system of beliefs? Yes. But this doesn't mean we aren't capable of sorting out what I call "proper" hinge beliefs from "improper" ones. The question becomes, are there good reasons to reject or doubt what they consider a hinge belief? If there are good reasons to doubt, then it's not a hinge. The fact that we're constantly arguing over, belief in God, shows that at least some doubting is warranted, if not most or even all doubts are warranted. It's certainly not like doubting that there are objects that exist in space. I can't understand what a doubt about the existence of objects would even entail. However, I can and do understand doubting the existence of God; and even though my e.g. at the beginning of this paragraph is more extreme, the same point holds.

Not to those who are convinced otherwise. To doubt it would put everything, their whole system of beliefs, into doubt.

Is there any support in Wittgenstein for the notion of a "proper hinge"? — Fooloso4

Of course they're convinced, which is why they consider it a hinge.

One could argue based on some of Witt's remarks that there are hinges of different kinds and that what's considered a hinge at T1, might not be at T2. We acknowledge that hinges change and that some of these changes are more pronounced than others. Wittgenstein doesn't use some of my terminology, but that's because I'm trying to expand on Witt's ideas. I'm not saying that all of my remarks can be supported by passages in OC or anywhere else. My remarks are a combination of my conclusions based on passages in OC, and my expansion of his ideas whether they agree or not.

My view is that belief in God is not a hinge belief.
— Sam26

In an earlier post you said: — Fooloso4

For many religions, belief in God is a hinge.
— Sam26

I'm not saying that people don't use it as a hinge. I'm saying it's not a proper hinge. There could be some beliefs within any system, even ones that contain myths, that are viewed as hinges. What makes a belief a proper hinge is that it doesn't make sense to doubt it (what does making sense here mean?). Doubting that there is a God makes perfect sense. It's nothing like doubting there are objects, or hands, or minds, etc. People may act as though it's a hinge (belief in God), which shows they believe it's a hinge, that's all.

There seem to be certain core beliefs that most systems of belief recognize as hinge. In other words, there are overlapping systems of belief that contain the same core beliefs (hinges), but they also contain other beliefs, considered hinges, but not recognized as such within those other systems. So, you end up with systems with competing hinge beliefs. Sorting this out happens over time.

I would just repeat that a claim to know is not knowledge in the sense of definitely knowing the truth of some proposition but is rather merely belief. — Janus

I believe this is incorrect, and it's a misunderstanding of what it means to know. I assume your use of the phrase "definitely know the truth" means to know with 100% certainty. Most of what we claim to know is not known with absolute certainty. Most of what we claim to know is what's probably true or likely the case, and this follows from logic (inductive reasoning). I think your idea of knowledge is too restrictive.

Also, a strong inductive argument wouldn't be considered "mere belief," since it would have strong evidence to support it. A mere belief to me is a belief that's based on no evidence or very little evidence, like an opinion.

He does not agree with your claim that hinges are not epistemological because: — Fooloso4

I know that he doesn't agree, I've talked with him and listened to his lectures on Youtube. My point in bringing him up was that he talks about how a religious epistemology might try to use belief in God as a hinge, i.e., as an arational belief. My view is that belief in God is not a hinge belief.

I have followed his disagreements with other philosophers who hold a similar position to mine. So, I'm familiar with his interpretation of Wittgenstein and his view on hinges.

I read Pritchard's paper on Hinge Epistemology. The first thing to be noted, as can be seen in the title, is that he regards hinges as epistemological. — Fooloso4

I know that, what's your point?

I'm not sure what you mean.

What is the nature of a hinge belief? What if someone's world picture includes belief in God as a hinge belief? Or, what if another world picture excludes belief in God as part of their hinge beliefs? Can we just decide whether this or that belief is a hinge? And, if for example, belief in God is a hinge, then there is no need to justify the belief as true or false, since they're arational beliefs. Does Wittgenstein address this problem, or do we end up with conflicting hinge beliefs? Dr. Duncan Pritchard often mentions this in his papers and his lectures. I believe Wittgenstein does address this issue.

"I should like to say: Moore does not know what he asserts he knows, but it stands fast for him, as also for me; regarding it as absolutely solid is part of our method of doubt and enquiry (OC 151)."

It seems clear that Wittgenstein is not only saying Moore's use of know is a misuse, but also that it's not knowledge. The beliefs (arational and hinge beliefs) Moore claims to know are the bedrock, foundation, and solid "...part of our method of doubt and enquiry." It forms a whole system of beliefs that "...characterize the way [we] judge, characterize the nature of judgment (OC 149)." The "nature of judgment" includes our epistemological language games and our language games of doubting. This means that justification and truth are an outgrowth of what stands fast, which is why, generally speaking, hinge beliefs are not justified and not true or false. How can this be? There is no how or why it's simply how we act. "Why do I not satisfy myself that I have two feet when I want to get up from my chair? There is no why. I simply don't. This is how I act (OC 148)."

Does this mean that the system of our judgments doesn't change, of course not, it just means that at any given point in time, there is a system of judgment that we don't question. Some of the beliefs in the system will remain unchanged and some will be removed, and others added, but the system will always be there as part of our bedrock beliefs. That there is a system of judgment is unchanging, it can't be otherwise. There is a limit to reason, to justification and truth, and it's an arational system of beliefs.

Do I think Wittgenstein is correct? Absolutely, and it changes the nature of epistemology, and moreover, it shows the limits of epistemology. I believe many philosophers and thinkers have overlooked Wittgenstein's final remarks.

The most difficult part of Wittgenstein's epistemology is to understand the groundlessness of our epistemology. The whole system is predicated on arational beliefs, and this is what is so different about Wittgenstein's approach to knowing and doubting. I believe that if you don't see this, you're missing the core of what Wittgenstein is saying.

"Must I not begin to trust somewhere? That is to say: somewhere I must begin with not-doubting; and that is not, so to speak, hasting but excusable: it is part of judging (OC 150)."

"When Moore says he knows such and such, he is really enumerating a lot of empirical propositions which we affirm without special testing; propositions, that is, which have a peculiar logical role in the system of our empirical propositions (OC 136)."

The propositions Moore claims to know, viz., those listed in his paper A Defense of Common Sense are the propositions Wittgenstein is referring to. Besides the most commonly used of Moore's statements "I know this is a hand," others include, "There exists at present a living human body, which is my body," and (paraphrasing) "There are other human bodies of the same class that have lived on Earth and have had many different experiences." These are the propositions Wittgenstein is referring to as empirical propositions that we affirm without special testing. In other words, we don't normally need a justification (epistemologically) for these beliefs. These are hinge propositions (I prefer to call them hinge beliefs), and they fulfill the logical role of being bedrock, foundational, or basic to our whole system of epistemological language games. It's where justification ends (no special testing required). Why? Because special testing or justification gets its life from these hinge beliefs. Not only do these beliefs give life to our epistemological language games, but they also give life to the language games of doubting. Such beliefs also reflect an ungrounded way of acting, which is at the core of our world picture or inherited background.

And where it's proper to give a justification for Moore's propositions, i.e., the exceptions, then these propositions are not hinges. So, they can function as proper propositions in certain contexts, but not generally. As I've mentioned elsewhere, and where I've expanded on what I think follows from OC, is that these beliefs at their core are pre-linguistic beliefs, shown in our actions.

It's not only Moore's use of know that is problematic, but saying these hinge beliefs are generally true is also problematic in similar ways.

Yes, we do disagree. I don't think we are likely to change our opinions now, but we have both over time changed our understanding to some degree. So, I do think there is value in discussing and defending our take on things. In defending our views we go back to the text and sometimes we find something new. — Fooloso4

I'm not saying there's no value in discussing and defending these ideas because there is, and I know that others are reading as we write. The frustration is that people are constantly misinterpreting things, so I have to keep repeating myself. I think I'm being clear, but not so much apparently. I find it an agonizing process, but I can't stop. I stop for a bit, and then in a few months, I'm right back at it. It's a love-hate relationship.

We disagree, I'm moving on.

"Can one say: "Where there is no doubt there is no knowledge either (OC 121)." The doubt, in the sense of challenging one's knowledge claim, is essential to what it means to have objective knowledge. Otherwise, we end up with pronouncements like Moore's, as if the pronouncement itself is enough. It also seems to be why Wittgenstein says in OC 4 to consider the negation of these kinds of propositions. If the negation doesn't make sense, then it's not epistemological it's a hinge. The epistemological use of "I know..." has to make sense when considering its negation. If it doesn't then it's just an expression of a hinge belief. It's the doubt that separates the epistemological from the hinges. In the former the doubt makes sense, in the latter it doesn't.

We have to remember that Wittgenstein never finished this work (OC), so it hasn't been edited. We don't know what passages would have been left in, and which passages would have been removed.

With regard to knowledge and doubt in On Certainty:

6. Now, can one enumerate what one knows (like Moore)? Straight off like that, I believe not. - For otherwise the expression "I know" gets misused. And through this misuse a queer and extremely
important mental state seems to be revealed.

What is this mental state? — Fooloso4

The mental state Wittgenstein seems to be referring to is the mental state of conviction. Moore's use of "I know..." is just that, a conviction of certainty. In OC 42 Witt refers to what is expressed by tone of voice and gestures (expressing a conviction), which fits Moore's use of "I know..." as he pronounces "I know this is a hand," by raising his hand before an audience. It's not an epistemological use of the words "I know..." where one is expressing a justified true belief.

In OC 7 Witt points out that our lives show (by our actions) these kinds of hinge beliefs, for example, by getting the chair or shutting the door. These are the subjective certainties of our world picture, which is how we act in the world. It's a misuse of know in the epistemological sense, we don't justify these kinds of beliefs, which is what Moore is trying to do and why Witt is criticizing his use of know. If OC 7 isn't about one's inner certainty, then it would be making the same mistake Moore makes.

Just to reiterate, there's a difference between one's inner subjective certainty (or using know as an expression of a conviction) and the epistemological use of "I know..." as an expression of objective certainty (knowledge). Witt uses know and certain in both ways, and it's important to distinguish between the two.

Knowledge claims are epistemological. Justification does not mark a distinction between epistemological and non-epistemological knowledge claims. — Fooloso4

Again, what I'm saying is that there are uses of the word know, as Witt points out, that are not epistemological. For example, "I know...," as an expression of a conviction, which is what Moore's use of know amounts to. This is a non-epistemological use; it refers to how I feel about a belief.

Science is a form of knowing in a participatory and a practical sense. We know the world, in the sense of participating in it, via science. It is practical too in the that it is a practice, a know-how. Propositional knowledge though, it seems to me, requires observation. I know I have hands because I can see them, observe myself using them and so on. I know it is raining when I am out and I feel the rain on my body and see the drops falling. In those kinds of cases, of which there are countlessly many in our lives, we cannot be mistaken, barring faux-doubt and bizarre thought-experiment scenarios, which I don't believe deserve our concern. — Janus

Science uses the same justification methods we all do, logic (inductive and deductive reasoning), sensory experience (observation), and testimony (peer reviewed papers, lectures, etc). It's just that science is generally more precise with these methods than the general public. Most knowledge in general is practical, not just science. Moreover, science draws conclusions based on whatever method of justification it's using, and these conclusions are in the form of propositions. If science presents a theory based on experiments or mathematical models, then someone probably believes the conclusions are either true or false. If they believe they're true or false, they're using propositions. Most all of what we know is in the form of propositions.

Knowledge can come in the form of a skill (know how) or in the form of a belief. Mostly when we talk about knowledge we're talking about beliefs not knowledge as a skill (like riding a bike or conducting skillful experiments). Although skills overlap with knowledge as a belief.

When you say "So, I could say without sounding weird that I have good reasons to believe I know X, but that there is a small chance I could be mistaken." I have no problem agreeing with you because it is not a claim that I know, but a claim to have good reason to believe that I know. And this highlights the strangeness of saying that I could know, without knowing that I know. For me, if I don't know that I know, as I say I do in cases like 'I am a human being' 'my body is bilaterally symmetrical (more or less)', I have hands and feet'. 'My head sits on my shoulders' and so on endlessly, then I would say instead that I don't know, but I believe or don't believe this or that, or I reserve judgement. — Janus

A claim to have good reason to believe X is partly what we mean by know. Good reasons are how we justify many of our beliefs and why we make claims that a proposition is true. It is a claim to know.

Part of Wittgenstein's argument against Moore is that we don't know we have hands. The hinge belief that we have hands is just part of the world picture we have along with a million other things, but it's not knowledge. I believe Witt is correct about this.

I see, not knowing and doubting, but believing and doubting as more inextricably tied. The problem I have with the idea that knowing involves uncertainty or defeasibility, is that it seems weird, inconsistent or incoherent. to say that you know, but that you could be mistaken. — Janus

It could simply mean that your inductive reasoning, which is a legitimate form of knowing is only probable (most of science is inductive). So, I could say without sounding weird that I have good reasons to believe I know X, but that there is a small chance I could be mistaken. This happens all the time. Evidence changes and so do our conclusions. I think the problem is when we conflate the meaning of knowledge as JTB for example, and one's claim to knowledge, they are two different things. The definition is one thing, that is what it means to know, but your inductive claim doesn't have the same force of necessity (if necessity is the correct word).

Epistemological considerations may come much later but knowing and doubting do not. It is not clear what the distinction you are making between knowing and doubting and their epistemological uses. If the point is that epistemology as an branch of philosophy arises later then yes, of course. — Fooloso4

Witt seems to point to two senses of know and certainty throughout OC. He talks about using know as an expression of a conviction which is not an epistemological use. He also talks about subjective certainty which is the same as know when used to express one's conviction. This is what I mean by non-epistemological uses of these words. An epistemological use of these words includes the proper justification and their truth.

Since hinges can and do change, even if only rarely and slowly, epistemological considerations are not off the table — Fooloso4

While it's true that most hinges can and do change, some don't. I gave these examples earlier, but you seem to ignore them or you're not reading everything. My examples include, there are objects, there are other minds, we have hands, etc. It's hard to see how there are objects could change.

If you going to critique what I say at least read with more care. That said, I'm sure we have disagreements nothing new here.

I'm saying that knowing and doubting as epistemological uses are more sophisticated language games. Knowing and doubting does not occur as an epistemological language game when speaking of hinge beliefs, generally. So, if you're speaking in terms of primitive man there is no knowing and doubting epistemologically. And, even if we're talking about modern man and their language games hinge beliefs also fall outside epistemological considerations.

OC 3 is just an example of where it might be proper to doubt and how we might satisfy that doubt. Moore's use is not such a case.

7 is referring to a subjective knowing and certainty. That's my interpretation.

None of the rest of your e.g.'s hurt my position. You don't seem to be following my position carefully. At least that's what it seems to me.

But recall that Wittgenstein regarded the ordinary meaning of "to know" to not imply infallibility, in the sense that even if a fact P necessarily implies another fact Q, "knowing that P" does not necessarily imply Q. — sime

Right, he never implies that "to know" means some infallibility on our part.

I don't think Wittgenstein would use phrasing like "P necessarily implies some fact," or what others use, viz., "P if and only if P," etc.

This stems from his epistemic consideration that in a literal sense nothing is knowable in the sense demanded by a philosopher. And yet he appreciated that everyone including himself ordinarily use the verb "to know" all the time. Therefore he concluded that the ordinary meaning of "to know" isn't an insinuation of ideal knowledge. — sime

Philosophers don't, as a general rule, hold to the notion that knowledge implies infallibility if that's what you're implying. Inductive reasoning is probabilistic, so any knowledge gained by inductive reasoning is not infallible by definition. I think Wittgenstein's point is that some uses of "I know.." are not epistemological as in Moore's case, at least that's part of Witts point.

What I am emphasizing here is what Wittgenstein says in On Certainty in the following:

110 “….As if giving grounds did not come to an end sometime. But the end is not an ungrounded presupposition: it is an ungrounded way of acting.” — Richard B

Yes, that's an important part of his thinking in OC.

"Giving grounds [justification], however, justifying the evidence, comes to an end;--but the end is not certain propositions' striking us immediately as true, i.e., it is not a kind of seeing on our part; it is our acting [non-linguistic], which lies at the bottom of our language game (OC 204)."

Wittgenstein's ideas seem to build on each other. At the bottom, i.e. the grounding or the world picture, then we have our actions (non-linguistic actions) within that grounding. On top of this comes a primitive language, then more sophisticated language games like knowing and doubting. Knowing and doubting come much later, it's parasitic on the world picture.

"The reason why the use of the expression "true or false" has something misleading about it is that it is like saying "it tallies with the facts or it doesn't", and the very thing that is in question is what "tallying" is here (OC 199)."

It seems very easy to say that a proposition is true because it tallies, mirrors, corresponds, etc. with the facts, but in Moore's case what does it mean? Moreover, what does it mean for any proposition to tally with the facts? There must be a way of deciding for or against a proposition (OC 198). Some propositions are determined to be justified and true based on what method of justification we're using, for example, logic, sensory experience, testimony, linguistic training, etc. To determine how most propositions are true we use one of these justification methods. The question though, for Wittgenstein has to do with certain kinds of propositions, Moorean propositions, which hold a special place in our system of beliefs, viz., the grounding of our epistemological talk of justification and truth. If justification comes to an end with hinges, then tallying loses its meaning with hinges, which seems to be why the question "What is tallying with the facts?"

"Really 'The proposition is either true or false' only means that it must be possible to decide for or against it. But this does not say what the ground for such a decision is like (OC 200)."

My interpretation is that the ground refers back to the world picture or inherited background, i.e., it grounds our very talk of justification and truth. Moore doesn't see that bedrock doesn't need grounding; it is the ground. Indeed, most of us don't see it. This solves the infinite regress problem, viz., where does justification end?

Wittgenstein's point is that no justification is required. Certain propositions, viz., hinge propositions are generally outside our epistemological language games.

"What does this mean: the truth of a proposition is certain (OC 193)?"

"With the word 'certain' we express complete conviction, the total absence of doubt, and thereby we seek to convince other people. That is subjective certainty.

"But when is something objectively certain? When a mistake is not possible. But what kind of possibility is that? Mustn't mistake be logically excluded (OC 194)?"

Wittgenstein uses certain in two different senses in OC, subjectively certain, as an expression of a conviction or feeling about a belief, and objectively certain, which is another way of expressing a piece of knowledge as JTB. So, certainty and knowledge both have their subjective and objective counterparts, and they are often confused.

OC 194 brings up a very interesting point, i.e., the tendency is to say, "I know...," and here one thinks one is using know in the epistemological sense (as Moore's does), as a guarantee that one knows, as if a mistake is not possible. However, if a claim to know is in itself knowledge, it would seem that knowing would lose its force, it would be akin to a conviction, opinion, or intuition. Knowledge must stand up to the doubt, "How is it that you know?" Note that with a mere belief, one might respond to the question "Why do you believe that?" with the answer "I just do," and that's acceptable as a mere belief; but a claim to knowledge as JTB requires more, it requires that the belief be justified and true. And of course, Wittgenstein in challenging Moore's use by asking what would count as a justification for "I know this is a hand." Wittgenstein is telling us that Moore's use of "I know..." is akin to an expression of a conviction, not objective knowledge as Moore thinks it is. Of course, this brings us full circle, viz., that the propositions that Moore retails as knowledge hold a special place within our world picture. Moore doesn't know, in his context, what he thinks he knows.

There is a lot to unpack here, and I've just scratched the surface.

"Even if the most trustworthy of men assures me that he knows things are thus and so, this by itself cannot satisfy me that he does know. Only that he believes he knows [my emphasis] (OC 137)."

There is a side issue with knowing that seems to get conflated with what we mean by knowledge (JTB), and what we claim as knowledge. A claim to know, even if one believes that they have the proper justification, doesn't always equate to knowing. This seems obvious, and yet people think that there is some problem with JTB because one can seemingly have a belief that's justified and true, and yet that belief can turn out to be false. Claiming to know is not necessarily knowing. We often believe we know, but later find out that we didn't know. It's simply a difference between one's claims and reality, they don't always match. Moreover, most of what we know is probabilistic and subject to what we think is likely the case, not what is necessarily the case. Given the probabilistic nature of most of our knowledge, it's reasonable to conclude that sometimes what we believe is justified and true, is simply false. This is just part of the nature of our claims and not a flaw in how we define knowledge (JTB). Within any system of beliefs, there will always be some false beliefs, even if we think those beliefs are well-established.

At the bottom of our epistemological use of "I know..." is an ungrounded way of acting, in other words, justification comes to an end. It ends with "...a lot of empirical propositions which we affirm without special testing; propositions, that is, which have a peculiar logical role in the system of our empirical propositions (OC 136)." It seems clear that Wittgenstein is referring to our world picture or our inherited background.

"The propositions, however, which Moore retails as examples of such known truths are indeed interesting. Not because anyone knows their truth, or believes he knows them, but because they all have a similar role in the system of our empirical judgments (OC 137)." It's the role hinges play in our system of judgments that's important, and it's certainly not about whether they're true or false. "We don't for example, arrive at any of them as a result of investigation (OC 138)." If someone wants to say they're true, then I ask, "How do you know they're true?" If you point to some criteria for their justification, then I believe you're missing Wittgenstein's point.

I think sometimes we lump hinges into a very large pot, as though they're all the same. However, that there are other objects or other minds isn't going to change, at least as far as I can see.

Watch out @schopenhauer1 the Wittgensteinians will take over the thread. :yikes:

It seems to me that knowledge and doubt are two sides of the same coin, i.e., you can't have one without the other. "Can one say, 'Where there is no doubt there is no knowledge either (OC 121)."

One could use the word doubt in a way similar to expressing an opinion, viz., there is no justification or very little justification for the doubt, similar to a feeling or intuition. However, just like many of our opinions, it generally carries very little weight. Just as knowledge is superior to mere belief, doubting backed by good reasons or good evidence is superior to a doubt that lacks some form of justification.

Some expressions of doubt are senseless. For example, doubting that there are other persons, grounds for doubt are lacking, everything speaks in favor of there being other persons and nothing against it. What would count as a grounding for such a doubt? "And couldn't we peacefully leave him to doubt it, since it makes no difference at all (OC 120)?"

"If you tried to doubt everything you would not get as far as doubting anything. The game of doubting itself presupposes certainty (OC 115)."

What is the certainty that is presupposed? Well, we've been talking about this in the previous posts, viz., the world picture or inherited background. Doubting by its very nature requires a place of certainty. "If you are not certain of any fact, you cannot be certain of the meaning of your words either (OC 114f)."

There is an important point about doubting that's similar to a point raised in earlier posts about knowing, viz., both have uses that point to an inner feeling; Knowing as an expression of conviction and doubting as an expression of intuition or a feeling of unease. Both of these uses are proper, but they are different from the uses of these words in an epistemological context.

"And isn't that what Moore wants to say, when he says he knows all these things?--But is his knowing it really what is in question, and not rather that some of these propositions must be solid for us (OC 112)?

Wittgenstein makes the point that some propositions must be solid for us. This is important in terms of what can be rationally doubted within our world picture or inherited background. However, given how broad our world picture is, there will inevitably be false beliefs within it, so what might be a hinge at T1, might not be at T2. In the past, I've mainly focused on hinges that tend not to change or that change very little over time, but Wittgenstein's hinges are much broader in scope. In other words, Wittgenstein's hinges would include actions (linguistic and non-linguistic actions) within any system of belief, even beliefs that are mere myths. There are groups of language games within these various systems that support the system, including epistemological language games. For many religions, belief in God is a hinge. So, we end up with competing systems, with hinges in one system that aren't hinges in another system. What's solid in one system won't be solid in another, and what is doubtable in one system may not be doubtable in another.

That said, certain hinge beliefs ground all of our systems, and these hinge beliefs tend not to change or change very little over time. Again, examples include: "There are other minds," "There are objects," "We have hands," and "The Earth has existed for a long time, etc." These hinges should be in a group of their own because they tend to be the most solid and beyond the reach of any reasonable doubt. They seem to be core hinges.

"And now if I were to say 'It is my unshakeable conviction that etc.', this means in the present case too that I have not consciously arrived at the conviction by following a particular line of thought, but that it is anchored in all my questions and answers, so anchored that I cannot touch it.

"All testing, all confirmation and disconfirmation of a hypothesis takes place already within a system. And this system is not a more or less arbitrary and doubtful point of departure for all our arguments: no, it belongs to the essence of what we call an argument. The system is not so much the point of departure, as the element in which arguments have their life (OC 103, 105)."

Of course, this refers again to the "inherited background or world picture" that forms the system in which we have our forms of life, language games, and our talk about epistemology. This also includes things that are not only true but also false, which explains why the riverbed of hinges can change. Some hinges are more fixed than others and the changes are more imperceptible.

Now that I think more about it @Fooloso4 there are some hinges that tend to be more immutable. For example, that we are beings that move through space, that I'm a being separate from other beings, that there are other minds, other objects, etc. These may even be necessarily hinges given the laws of the universe. I don't know if I've brought this up before, but maybe that's where you got the idea from. So, there are hinges that range along a kind of scale, some being more or less immutable, and most not being immutable at all.

Yes, and this is just what he did, he was in front of people when he expressed his "common sense" view that he knew he had a hand. It's not always as easy to spot the linguistic problem as you might think.