My interpretation is that J is not questioning whether global doubt is incoherent, but is asking why grammar should be considered sufficient to settle the issue. In other words, what explains why grammar imposes the limits it does? — Esse Quam Videri

Yes, though at this point I do wish we had a different term than "grammar," since grammar has such a specific meaning within language. Obviously none of us is saying that English grammar can settle philosophical questions. What sort of grammar, then, are we referencing? I tend to translate it as "mutual conceptual coherence," but perhaps there are other ways.

Grammar is the surface expression of deeper constraints built into what it means to doubt, inquire, and correct at all. — Sam26

A good insight, and a potential answer to the question raised above. Again, it allows us to turn away from the idea that language is actually the issue. Doubt and inquiry are practices, not units of language.

global doubt misfires because it cancels the very conditions that make doubt an intelligible, or an answerable activity — Sam26

Yes. And I'm focusing on these "very conditions" -- how should we describe them? What ontological commitments are involved, exactly? It sounds like all three of us see the same basic picture, but we're each working to give the most perspicuous account of what we see. I may be over-obsessing about the idea of "distinguishing appearance from reality," but is this really what we must claim for justificatory practices? To ask it differently: Could we instead claim that we distinguish truth from opinion? Is our warrant for talking about truth any stronger than our warrant for talking about reality? It's a genuine question; I'm not sure.

I feel like I keep repeating myself. When I say, “the conditions that make doubt intelligible,” I mean the basic setup that makes checking and being checked possible. For any practice of inquiry to work, it has to treat some outcomes as settled and others not. Otherwise “I doubt,” “I tested,” and “I corrected myself” become empty statements.

We don’t have to start with the heavy phrase “appearance vs reality.” We can start with something leaner. For instance, settled vs unsettled, correct vs incorrect, passes the check vs fails the check. Those distinctions are already enough to rule out global doubt, because global doubt tries to remove the very idea that anything could ever count as settled.

“Truth vs opinion” can express the same structure, but only if truth means “what would be correct even if no one endorsed it.” If “truth just means “what our group happens to treat as correct,” then the difference between error and correction disappears into sociology. So, the real commitment isn’t a grand metaphysics of Reality with a capital R, it’s the thinner claim that correctness answers to something beyond mere endorsement. Call that truth, call it reality, call it constraint, it’s the same role.

I believe that’s the ontological answer here, not a theory of what exists, but the insistence that inquiry isn’t just opinion-management, it’s answerable to what settles these epistemological questions.

I agree with you, though many would disagree. I was curious where you would fall on the question. Sounds like we broadly agree on these issues. — Esse Quam Videri

Even if you were omniscient someone would disagree. It means nothing, don't you think?

Continuing with paper...
Post #13

8. Broader Consequences for Epistemic Life Today

The refinement offered by JTB+U is not meant to remain at the level of conceptual reconstruction. Its point is to clarify how our epistemic practices actually work, and to make visible the distinctions that are now repeatedly blurred. In many contemporary settings, the appearance of support is treated as if it were justification, fluency is treated as if it were understanding, and conviction is treated as if it were certainty. The result is not merely disagreement. It is a weakening of the grammar of knowledge, a drift in the very criteria by which we distinguish knowing from persuading, and truth from mere plausibility.

One consequence of the framework is that it restores the place of justification as a public practice. When justification is treated as something private, or as an inner feeling of confidence, the discipline of epistemic life collapses into rhetoric. JTB+U makes explicit that justification depends on shared criteria, on the ability to locate a belief within an established route of support, and on the willingness to submit that standing to correction. This is why the language-games of knowledge depend on practices of challenge and withdrawal. A belief that cannot be corrected within a practice is not thereby strengthened. It is severed from the ordinary conditions under which justification has its point.

A second consequence is that the model clarifies the role of testimony in a world saturated with information. Testimony is not a lesser route. It is among the most common routes in ordinary life. Yet the present environment often treats testimony as interchangeable with assertion, as if the mere existence of a claim in circulation were enough to give it standing. JTB+U makes clear that testimony has standing only within the practices that grant it, and that this standing depends on criteria that are often ignored in modern informational contexts. When those criteria are weakened, testimony does not disappear. It becomes unstable, and epistemic life becomes susceptible to persuasion that imitates the surface of justification.

A third consequence concerns the probabilistic character of justification. Much of what we count as knowledge is not secured by absolute certainty. Our justificatory practices are often graded, and they frequently operate under conditions of limited information. This is not an embarrassment to epistemology. It is part of the grammar of our epistemic life. The mistake is to treat this fallibility as if it implied that knowledge is impossible, or that the classical model must be abandoned. JTB+U instead clarifies how fallibility and knowledge coexist. We can have knowledge without having what philosophers sometimes treat as conclusive proof, because the standing required for knowledge is determined within a practice, under disciplined constraints, against a stable background of bedrock certainties.

This is also where the distinction between the different senses of certainty matters. Subjective certainty is conviction. It can be intense, and it can be sincere, yet it does not settle anything about truth. Hinge certainty is bedrock, it stands fast and makes doubt possible, yet it is not knowledge. Epistemic certainty is the kind of stability a belief can have within a practice of justification, where the belief is resistant to relevant challenge and supported in the way the practice requires. Absolute certainty belongs to logic and necessity. Modern discourse often collapses these into one undifferentiated notion of certainty, and the collapse produces confusion. Conviction is treated as evidence. Bedrock is treated as dogma. Logical necessity is treated as a demand for knowledge. JTB+U separates these senses and returns each to its proper use.

A further consequence is that the framework explains why disagreement can persist even among sincere and competent thinkers. Disagreements are not always disputes over evidence. They can arise from differences in the background against which evidence is assessed, from differences in how concepts are being used, and from differences in which defeaters are treated as relevant. None of this makes truth relative. It shows that our practices of justification are complex and that the stability of knowledge depends on more than the production of arguments. When we recognize this, we are less tempted to treat disagreement as evidence of irrationality, and more able to locate what is actually at issue.

Finally, the framework provides a disciplined response to the current pressure to treat epistemic life as a contest of narratives. Persuasion is not the same as justification. A persuasive claim can be memorable, emotionally forceful, and socially reinforced, while still lacking standing within a practice of justification. JTB+U gives us a way to say this without moralizing. It identifies where the grammar breaks down. The guardrails make the point concrete. No False Grounds blocks claims whose support depends on what is not so. Practice Safety blocks claims that succeed only by coincidence or rhetorical timing. Defeater Screening blocks claims that remain compelling only because relevant challenges have been excluded or ignored.

Wittgenstein’s distinction between criteria and mere signs is useful here. Many things accompany knowledge: confidence, fluency, repetition, even social approval. Yet these are not what justify a claim. They are at best symptoms, and often only disguises. The criteria for knowledge belong to the practice: the routes by which justification is given, the guardrails that discipline it, and the ways a claim can be corrected, withdrawn, or defended when challenged. When those criteria are replaced by signs, epistemic life becomes vulnerable to persuasion that imitates the surface of justification.

In this sense, the account is realist without dogmatism. It affirms truth as the success condition. It affirms the public character of justification. It affirms the necessity of bedrock certainties without treating them as items of knowledge. It affirms fallibility without conceding skepticism. It also encourages a kind of epistemic humility that is not a retreat from truth but an acknowledgement of the limits built into our practices. The point is not that we should doubt everything. The point is that we should recognize what must stand fast for justification to function, and then take seriously the discipline by which beliefs earn their standing as knowledge within the language-games we share.

Even if you were omniscient someone would disagree. It means nothing, don't you think? — Sam26

Ha. Indeed. I try to see disagreement as an opportunity to learn something new or refine what I already know, hence my curiosity.

I basically agree with 's reply here. There is a minimal metaphysical commitment that I would say is unavoidable; namely, that there is something that makes judgments true or false, independently of our taking them to be so. That’s enough metaphysics to ground inquiry — and no more than that.

I'm curious. What's fueling your "obsession" with the metaphysical question? Do you suspect that there is more to it than this?

Continuing with paper...
Post #14

9. Objections and Stress Tests

Before closing, it is worth testing the framework against a few cases that are often used to pressure classical accounts of knowledge. The point is not to chase intuitions, but to show how the routes and guardrails clarify why some beliefs have the standing required for knowledge and why others do not, even when the surface looks similar.

Fake barn environment. Consider the case in which a person looks at what appears to be a barn, forms the belief “that is a barn,” and happens to be looking at the only real barn in an area filled with convincing façades. The belief is true, and from the person’s point of view the perceptual situation seems ordinary. Yet the belief lacks the standing of knowledge. JTB+U does not need a new condition to explain this. The belief proceeds through sensory experience, but the environment has altered the standing of that route. Practice Safety is decisive. In a setting saturated with decoys, the belief would easily have been false under nearby variations that the practice treats as relevant. The problem is not that perception stops functioning, but that the ordinary stability required for knowledge is not present. Defeater Screening also matters. The relevant defeater is built into the environment itself, namely that many barn-like objects are not barns. The point is not what the person privately considered, but what standing the belief has within a practice once that defeater is in play.

Testimony under distorted informational conditions. A second pressure point concerns testimony in an environment where repetition is treated as standing. Here the route is still testimony, but testimony has standing only within practices that supply criteria of credibility, provenance, and correction. No False Grounds blocks a common failure. Testimony can look supportive while resting on fabricated reports, altered media, or untraceable sources. A belief placed on such grounds can be compelling and socially reinforced, yet the support is defective at the point where the practice treats the defect as disqualifying. Practice Safety and Defeater Screening complete the diagnosis. A claim can be true by coincidence and widely repeated, while remaining unstable under ordinary informational variation. A claim can also remain persuasive only because relevant challenges are excluded rather than addressed. In either case, what is missing is not sincerity or intensity of conviction, but the standing a belief must have within a practice of justification to count as knowledge.

Human and AI hybrid cases. A third test concerns cases in which a person uses an artificial system as an aid. The temptation is to treat fluent output as knowledge, or to treat the user as having knowledge simply by receiving an answer. The framework clarifies the difference. A person can acquire knowledge with the help of AI only if the belief formed on the basis of the output is placed within a practice of justification that satisfies the guardrails. No False Grounds matters because an output can include invented citations or a false claim doing essential work. Practice Safety matters because slight prompt changes can produce incompatible outputs, which signals instability. Defeater Screening matters because relevant counter-considerations can be present and must be addressed within the practice if the belief is to have standing. This also shows the proper role of understanding. If the output is treated as a substitute for conceptual competence, then the belief can have the appearance of support while lacking the internal structure required for genuine justification. AI can be a powerful instrument within human epistemic life, but that does not collapse the distinction between producing true sentences and knowing.

What these tests show. These cases do not require a patch to JTB. They show that when justification is treated as a public practice with disciplined constraints, the difference between knowledge and lucky success is not mysterious. Truth remains the success condition. What varies is the standing of a belief within a practice, and that standing depends on the routes by which it is supported and on the guardrails that discipline that support. In this way, JTB+U does not replace the classical model. It clarifies what the model already presupposes when we speak carefully about what it is to know.

I basically agree with ↪Sam26 's reply here. There is a minimal metaphysical commitment that I would say is unavoidable; namely, that there is something that makes judgments true or false, independently of our taking them to be so. That’s enough metaphysics to ground inquiry — and no more than that.

I'm curious. What's fueling your "obsession" with the metaphysical question? Do you suspect that there is more to it than this? — Esse Quam Videri

On the minimal commitment, yes, I agree that it can ground inquiry. But are you also saying that philosophy can't or shouldn't be asking about what the "something" is that makes judgments true or false?

My perhaps obsessive concern with the appearance/reality question springs from my dislike of the term "reality" in philosophy. It's not that I think there's "more to it than this," but the opposite: I think there's less to it. I don't think we should say that epistemic justification can show us what is "real" -- though see @Sam26's point above, about how "truth," "reality" and "constraint" are all aiming at the same role in this discussion. Which is part of why I try to avoid "reality" as a term. I don't think it does much independent work. And at worst, it can blur the distinction between questions about being, and questions about thinking.

Which is part of why I try to avoid "reality" as a term. I don't think it does much independent work. And at worst, it can blur the distinction between questions about being, and questions about thinking. — J

That's a fair worry. Like you I would resist any attempt to blur this distinction, but I would equally resist any attempt to detach truth from reality. If truth were nothing more than coherence of belief, stability within practice or endorsement by a community then the distinction between truth and opinion, or error and disagreement would collapse. I would argue that the normativity of truth requires that claims are answerable to something that is not exhausted by belief, endorsement or correct usage. As @sam26 said, this "something" doesn't have to be a full-blown metaphysical picture of Reality with a capital-R, but it does have to be robust enough to make sense of correction, learning, discovery and the possibility of being wrong.

Thoughts?

Continuing with the final post of the paper.
Post #15

10. Conclusion

The classical model of knowledge as justified true belief remains a sound starting point, not because it answers every philosophical worry, but because it captures the grammar of our ordinary epistemic life. When we call something knowledge, we are not merely reporting a psychological state of conviction. We are placing a belief within a practice of justification and marking that it has succeeded in being true. This is why the model has endured. It reflects what we already do when we distinguish between mere opinion and beliefs that genuinely have standing.

The refinements developed here do not replace that model; they make explicit what the classical formulation leaves implicit. Justification does not operate in isolation. It functions within shared language-games and presupposes a background of bedrock certainties that stand fast for us. These certainties are not items of knowledge, and they are not established by further justification. They are foundational in a non-epistemic sense. They set the conditions under which doubting, checking, and justifying have their point. This is why the demand to justify everything does not express greater rigor. It reflects a misunderstanding of the role that what stands fast plays in our epistemic life.

Understanding, likewise, is not an optional addition to justification; it is internal to it. To justify a belief is to use the relevant concepts correctly within a practice, to move competently among their connections, and to recognize what counts as correction and withdrawal when the practice requires it. The beetle in the box makes the point vivid. If we treat understanding as an inward item, something to which one privately points as the basis of epistemic standing, we detach justification from the criteria that give it life. We do not strengthen knowledge by relocating its basis to the private interior. We dissolve the conditions under which the concept of knowledge functions at all.

These clarifications also reposition the role of Gettier in epistemology. Once justification is understood as a standing within an epistemic practice, disciplined by criteria of correct use and constrained by what stands fast, Gettier-style cases lose their supposed significance. They do not show that the classical model is inadequate, but that many discussions of Gettier rely on a conception of justification that fails to reflect how our epistemic practices actually operate.

To make these points concrete, I distinguished five routes through which justification typically proceeds: testimony, logical inference, sensory experience, linguistic training, and pure logic in its boundary-setting role. These routes are not ranked by epistemic importance. They reflect the order in which justificatory support most commonly appears in our language-games. Alongside these routes, I described three guardrails that express the discipline internal to justification: No False Grounds, Practice Safety, and Defeater Screening. These guardrails do not add new conditions to knowledge. They clarify what it is for support to count as justificatory within a practice and help explain why some beliefs that look well supported fail to have the standing required for knowledge.

The structural parallel with Gödel reinforces the same lesson from a different angle. Gödel’s results show that formal systems have limits that arise from their internal structure, limits that are not defects but conditions of the system’s character. Wittgenstein’s remarks on hinges show that justificatory practices have limits as well. Not everything that makes justification possible can itself be justified. The parallel is structural, not mathematical, but it is instructive. It helps us see that the presence of limits does not entail skepticism. It marks the conditions under which epistemic life can proceed.

The application to artificial intelligence illustrates why these distinctions matter now. Artificial systems can produce true statements, sometimes with impressive reliability. Yet knowledge is not merely the production of truths. It is true belief that stands within a practice of justification, governed by routes, constrained by guardrails, and framed by what stands fast. AI systems can assist human knowers and function as powerful instruments within our epistemic practices. But to treat them as knowers is to blur the grammar of knowledge at exactly the point where clarity is most needed.

What emerges, then, is an account of knowledge that is realist without dogmatism. Truth remains the success condition. Justification remains a practice governed by shared criteria. Bedrock certainties stand fast without becoming items of knowledge. Understanding is not a private achievement but a competence displayed in use. The result is not a new theory erected on top of the classical model, but a clearer view of its working parts and of the background that makes them possible. If there is a practical upshot, it is this: when the appearance of support is everywhere, the task is to recover the discipline of justification and to keep the grammar of “know” clear enough to do its work.

If truth were nothing more than coherence of belief, stability within practice or endorsement by a community then the distinction between truth and opinion, or error and disagreement would collapse. — Esse Quam Videri

Completely agree.

something that is not exhausted by belief, endorsement or correct usage. — Esse Quam Videri

Yes again, and @Sam26 certainly sees it this way too.

this "something" doesn't have to be a full-blown metaphysical picture of Reality with a capital-R, but it does have to be robust enough to make sense of correction, learning, discovery and the possibility of being wrong. — Esse Quam Videri

This is where I've been focusing. I think we've come a long way in clarifying what the "something" needs to do, but questions may remain. At this point I want to give myself time to read Sam's paper in its entirety, as so far I've only been responding to the original summary and subsequent discussion. Then I may be better able to say more.

Do you think hinges are real features of our epistemic life, or are they a philosopher’s invention to stop regress. — Sam26

I think this would take a whole separate thread, but my impression is that these kind of statements are not actually used nor are a functional part of justification, but are categorically separate, though my experience with On Certainty is much less than yours and, moreover, less than it should be to be anywhere near as sure as that sounds.

I do recognize our greater world is out there without which nothing we do would be possible, but I don’t see when anyone goes around pointing it out or claiming anything about it because it is so ubiquitous and uncontested as to be banal. No one is going to ask for justification if I say “The sun will come up tomorrow”, nor can I think of an example (outside of radical skepticism) where such a statement would be a final justification because I can’t imagine the request that would lead to it, nor anyone thinking that it would conclude a matter (of justification, not skepticism).

I think the fact that it is certain (as pure logic is) makes it desirable as an attempt to ensure closure with some sense of force, but I would think we should be able to agree that that kind of certainty is not necessary (a requirement) for justification of a belief, and I take that to be because the way justification works is not on a scale with certainty as the pinnacle (nor radical skepticism as its nemesis). More along your other points, the structure of each practice provides for the way in which justification is reached in a matter (including justification itself), not even taking into account an actual particular case.

All that is to say that I think the matter of when and where justification ends is not the antithesis of classic, philosophical skepticism. I take that world-ending skepticism to come from an initial and voracious desire for abstract, timeless universality that wipes out all ordinary, rational criteria of particular practices or cases. No fact is enough to satisfy it, but I think that’s because justification is not about being more abstract and general, but more specific and detailed.