Post #1
What JTB+U is claiming

My paper defends a practice-oriented refinement of the traditional JTB account. I call it JTB+U: “justified true belief” plus Understanding. My point is not to add a new requirement onto JTB as if we had discovered a fourth ingredient. My point is to make explicit something justification already presupposes in everyday epistemology, i.e., the competence to grasp what counts as support, what counts as error, and what would count as correction within a practice.

On this view, many familiar puzzles arise when we picture justification as something essentially private, an inward sense of being entitled (e.g. the use of know as an expression of a conviction), as if the fact that a belief feels well supported could stand in for the standards by which it is actually assessed. But in ordinary epistemic life, justificatory standing is not conferred by confidence or by an internal impression of rightness. It depends on the grammar of our practices, the criteria by which we count something as evidence, the ways we identify error, and the norms by which we correct it. When we bring that grammar into view, Gettier cases lose much of their force because many depend on a mismatch between seeming justified and having justificatory standing.

Upshot: I am not replacing JTB, I am strengthening it by making explicit the Understanding that is already doing quiet work inside justification.

Questions for critique:

Does the “+U” clarify anything real, or is it a relabeling.

Where would you draw the boundary between justification and understanding, if you think there is one.

What is your strongest reason to think Gettier still bites even after this move.

The spine of my paper will be covered in seven posts.

1. What JTB+U is claiming

2. What I mean by justification as practice grammar

3. What “Understanding” is doing

4. The guardrails (No False Grounds, Practice Safety, Defeater Screening)

5. The five routes of justification

6. Hinges as non-epistemic background

7. Gettier diagnosis and upshot

Should we comment as you go along or wait till you've presented the whole thing?

You can comment as I go along, but many of the questions about what I mean by this or that will be explained in later posts.

Post 2 of 7:
What I mean by “justification”

When I use the word “justification,” I am not talking about something private, a feeling of confidence, or a mere report of how things seem from a subjective point of view. I mean justificatory standing, the sort of standing a belief has when it is supported by the standards that govern a practice, standards for what counts as evidence, what counts as error, and what counts as correction.

That is why I sometimes describe justification in terms of grammar (Wittgensteinian grammar). The point is not that knowledge is “only language,” but that the difference between being entitled and merely thinking one is entitled is built into how our practices work. We learn what it is to justify by learning how claims are checked, challenged, repaired, and sometimes withdrawn. Those norms are not optional decorations added after the fact. They are part of what makes the idea of justification intelligible.

This is also why I emphasize the public character of justification. “Public” here does not mean popular agreement or institutional permission. It means that justification has criteria that can, in principle, be articulated, assessed, and disputed within a shared practice. A belief can be held with sincerity and conviction and still fail to have justificatory standing.

Upshot: justification is a normative standing within a practice, not an inner endorsement, and that is the background against which the “+U” move makes sense.

Questions for critique:

Do you think justificatory standing can be explained without appeal to shared criteria, or does that collapse into a purely psychological picture.

Is my use of “grammar” illuminating here, or does it obscure what is really going on.

Does “public in this sense” capture what we need for justification, or does it leave out something essential.

An interesting, well thought out, and well written OP. I have an overall question to help me decide whether to participate and then I’ll wait till you've posted everything.

These issues are things I've spent a lot of time thinking about. I'm trying to figure out if my way of seeing things compliments or contradicts yours. I take a very pragmatic approach--knowledge is meant to be used to decide how to act. Both your understanding and mine focus on what it means to justify potential knowledge. For me, the requirement is adequately justified belief. I define "adequate" as providing enough certainty about outcome for us to make a responsible decision. I have particular standards to apply to determine that.

So--does it make sense for me to participate?

Post 3 of 7:
What “Understanding” is doing in JTB+U

In JTB+U, “Understanding” is not a new mental ingredient added on top of truth, belief, and justification. It names a feature already at work in justification, the grasp of the concepts and inferential roles that make justificatory standards applicable at all. If justification is a standing within a practice, then understanding is the competence by which a person can genuinely participate in that practice, not merely mimic its conclusions.

Someone can hold a true belief and even cite a correct supporting data, while still failing to grasp what that support is doing, what would count against it, what would defeat it, and what would count as a relevant correction. In that situation the belief can look justified from the outside, and even to the person themselves, but the justificatory standing is fragile, because the person does not reliably track the mistake-conditions that the practice treats as decisive. Understanding, in this sense, is the operative structure of justification, the competence that makes justificatory standards genuinely operative rather than merely repeatable.

This is also why I resist treating “justification” as if it were only a list of supporting propositions. A list can be repeated by rote. Understanding is what makes the support more than a recitation, it is the ability to locate the claim within the space of reasons, objections, defeaters, and revisions that the practice recognizes. That is not infallibility, and it is not an impossible demand. It is simply the difference between having a standing and merely borrowing one.

Upshot: “+U” marks the competence that makes justificatory standards operative, it is not a separate add on.

Questions for critique:

Is this notion of understanding genuinely distinct from justification, or does it collapse into it.

Does tying understanding to error signals, defeaters, and correction make the account clearer, or does it over intellectualize ordinary knowing.

Can you think of a counterexample, a case where someone lacks this competence but still seems to have genuine justificatory standing.

Yes, it makes sense for you to participate, and I think your pragmatic approach can fit naturally with mine, as long as we keep the different uses of “certainty” from sliding into each other.

I divide certainty into different uses:

Subjective certainty, conviction, how settled a claim feels.

Hinge certainty, the bedrock that stands fast and makes inquiry and doubt possible at all.

Epistemic certainty, defeater resistant stability in practice, the kind of standing we treat as enough for responsible action within a domain.

Absolute certainty, logical or moral necessity.

With that in view, your “adequate certainty about outcome” sounds closest to what I call epistemic certainty, not absolute certainty, and not merely subjective certainty. In other words, it is not infallibility, and it is not just confidence. It is a claim having the right kind of stability under the relevant checks, given the stakes and the standards of the practice you are operating in.

Where our approaches might meet is that both of us think justiification is disciplined by standards. Where we might differ is that I frame those standards in terms of justificatory standing within a practice, including what would count as a mistake, what would count as a defeater, and what would count as a responsible correction. Practical stakes can raise the bar, but they do so by tightening what counts as adequate support, not by demanding absolute certainty.

So yes, participate. If you want a clean point of contact, tell me what your “adequacy” standards are in a concrete case, and we can ask how they relate to defeater resistance, false grounds, and practice safety, and which sense of certainty they are aiming at.

Post 4 of 7:
Three guardrails that discipline justification

If justification is a standing within a practice, it still needs discipline. Not every chain of support confers standing, and not every true belief that happens to be well supported counts as knowledge. In the paper I use three guardrails to mark common ways justification fails, even when a belief looks respectable.

No False Grounds (NFG). A belief cannot have genuine justificatory standing if the support it depends on is false, or if it is being carried by a false presupposition that is doing the real work. The point is simple: if the ground is false, whatever looks like support is a counterfeit support.

Practice Safety. A belief is practice safe when it is formed and maintained in a way that reliably tracks the mistake conditions recognized by the practice. This is not infallibility. It is the idea that the route by which the belief is held is not fragile, lucky, or insulated from the ordinary error signals that would count against it in a particular domain.

Defeater Screening. Even when the grounds look good, justificatory standing is undermined when there are live defeaters that have not been faced. A defeater is not merely a contrary opinion. It is a consideration that, if true, would remove or weaken the support, or would show that the apparent support is misleading. Defeater screening is the discipline of identifying and addressing such considerations, rather than ignoring them.

These are not meant as extra conditions stapled onto JTB. They are ways of making explicit the constraints that ordinary epistemic practice already applies when it distinguishes genuine support from luck, from illusion, and from rationalization.

Upshot: the guardrails do not add a new theory of knowledge, they articulate the failure modes that explain why “seeming justified” can diverge from genuine justificatory standing.

Questions for critique:

Do you think these guardrails capture real failure modes, or do they smuggle in something stronger than ordinary justification.

Is Practice Safety a useful idea, or does it collapse into defeater screening or into reliability talk.

Can you think of a case where a belief meets these guardrails and still intuitively fails to count as knowledge.

I will wait until you’ve posted everything and I’ve had a chance to read it. Then we can see where it goes from there.

Post 5 of 7:
Five routes of justification (non exhaustive)

In the paper I lay out five primary routes by which beliefs commonly acquire justificatory standing. The point is not to rank them or claim that every case fits neatly into a single category. The point is to map the main ways we actually come to know, so that we can ask where a claim is getting its support, and what standards and error conditions belong to that route.

Testimony. Most of what we know comes from others, ordinary reports, books, videos, expert claims, historical records, and lived witness. Testimony can confer justificatory standing, but it has its own standards: credibility, independence, competence, convergence, and the absence of relevant defeating information.

Logic (inductive and deductive reasoning). We justify beliefs by inference, sometimes strictly, sometimes probabilistically. Here the relevant standards include valid form where appropriate, good inductive support, sensitivity to base rates, and the ability to identify where an inference is overextended.

Sensory experience. Experience is a central route of support in ordinary life. It has its own error conditions: illusion, distortion, poor conditions, and conflict with other well established checks. Sensory experience does not need to be perfect to justify, but it must be situated within the ordinary corrective practices that make perception reliable in the domain.

Linguistic training. Some things are “known” because we are trained into a practice, trained to use terms correctly, to recognize criteria, to follow rules, and to distinguish correct application from misuse. This route is often invisible because it is basic to how we learn the grammar of our concepts, but it is indispensable for explaining how justification becomes possible at all.

Pure logic (boundary setting only). There are limits that are not empirical discoveries but logical constraints, what is possible, what is coherent, what follows from definitions, what collapses into contradiction. This route does not supply new facts about the world. It sets boundaries, clarifies entailments, and exposes category mistakes.

This five route map is not meant to replace the earlier guardrails. The guardrails discipline justification. The routes describe where justification is coming from. In any concrete case, the question becomes: which route is in play, what are its standards, and do the guardrails hold.

Upshot: the routes give us a practical way to locate a claim in the space of support, standards, and error conditions, without turning epistemology into a single method.

Questions for critique:

Are these five routes a helpful map, or do you think the categories blur in a way that makes the list misleading.

Do you think “linguistic training” deserves to be a distinct route, or is it better treated as part of the background of the other routes.

Is my use of “pure logic” as boundary setting clear, or does it need a different label.

:up:

Post 6 of 7:
Hinges and why justification has stopping points

At some point justificatory questions come to an end, not because inquiry has failed, but because the very practice of giving and asking for justification presupposes a background that is not itself justified. If you demand a justification for everything, including the conditions that make justification possible, you do not reach a deeper standard. You undermine the justification.

This is where hinge certainties come in. A hinge is not a hypothesis, not a conclusion, and not a belief held because we have evidence for it. It is something that stands fast in a practice, a bedrock commitment expressed in how we proceed, what we take for granted, what counts as doubt, and what counts as a mistake. Hinges are not the kind of things we arrive at by argument, but they are also not arbitrary. They belong to the inherited background against which reasons, evidence, and defeaters can have their force.

That matters for two reasons. First, it explains why the demand for ultimate proof is misguided. Proof and justification always operate within a framework, and the framework is not itself established by the same tools it makes possible. Second, it explains why skepticism so often feels powerful. Skeptical questions typically target hinges and treat them as if they were ordinary empirical claims. Then, when those hinges cannot be proven in the skeptic’s demanded way, skepticism concludes that nothing can be known. The mistake is grammatical. The skeptic is asking for a kind of justification that cannot apply to the role hinges play.

None of this licenses dogmatism. It is true that some hinges can shift as practices are repaired, methods change, or persistent error signals force a reorientation. But it is equally true that some hinges do not shift, at least not within anything we would still recognize as the same form of life. Their role is constitutive, they are part of what makes inquiry, correction, and assessment possible at all. Where a hinge does shift (e.g. we are objects separate from other objects), the change is usually not a matter of ordinary argument but a deeper reorganization of the practice itself.

Upshot: hinges are not additional reasons. They are the background that makes reasons and defeaters possible, and recognizing this prevents both regress and skeptical distortion.

Questions for critique:

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

Does treating skeptical challenges as hinge confusion actually answer skepticism, or does it merely set it aside.

Can you name a hinge you think my framework relies on, and say whether you think it should stand fast or be challenged.

Post 7 of 7:
Gettier, and why “seems justified” can mislead

Gettier cases are designed to make the traditional JTB account look inadequate. The familiar pattern is that a person has a true belief, and can cite what appears to be a justification, yet we hesitate to call it knowledge. The standard moral is that JTB is missing some extra condition. My paper argues that this moral is too quick, because it treats “justification” as if it were exhausted by having a supporting consideration that can be stated.

On the view I am developing, the key distinction is between a belief that looks justified, and a belief that has genuine justificatory standing within a practice. In Gettier style cases, the subject often has support that is either dependent on a false ground, or is insulated from the relevant mistake conditions, or is undermined by an undefeated defeater. In other words, the cases exploit a gap between seeming to meet the justification requirement and actually meeting it once the ordinary constraints on justification are made clear.

This is where the guardrails matter. If a belief depends on a false ground, No False Grounds blocks it. If the route is fragile and the belief is true by luck, Practice Safety blocks it. If there is relevant defeating information that has not been faced, Defeater Screening blocks it. The upshot is not that Gettier reveals a defect in JTB, but that Gettier is trading on an impoverished picture of justification, and once justification is properly described, the cases no longer force an additional condition.

This also brings the “+U” into focus. Understanding is not a decorative addition. It marks the competence by which a person can genuinely track what their support does, what would count against it, and what would require revision. A person can cite a reason and still be out of contact with those mistake conditions. When that happens, the belief can be true and can look justified, yet it lacks the stability we normally require for knowledge.

Upshot: Gettier cases do not show that knowledge needs a mysterious extra ingredient. They show that we should not confuse the appearance of justification with genuine justificatory standing.

Questions for critique:

Do you think Gettier cases still refute JTB even if we build in the guardrails and the “+U” clarification.

Is my diagnosis too dependent on relabeling the justification condition rather than answering the core intuition.

If you have a favorite Gettier case, post it and say which guardrail you think it slips past, if any.

Clarifications and terms (so we do not talk past each other)

Before continuing, I want to clarify a few terms that can easily be misunderstood.

What “+U” is and is not. In JTB+U, “Understanding” is not a new ingredient bolted onto JTB. It is a way of making explicit what justification already presupposes in ordinary epistemic practice, the competence to grasp what counts as support, what counts as error, and what would count as correction in the domain.

What I mean by “public.” When I say justification is public, I do not mean popular agreement or institutional permission. I mean that justification has criteria that can, in principle, be articulated, assessed, challenged, and corrected within a shared practice.

Practice Safety is not a demand for infallibility. Practice Safety means that the route by which a belief is held is not fragile or lucky with respect to the mistake conditions the practice recognizes. It is about tracking error signals in the domain, not about achieving certainty in the absolute sense.

What I mean by a defeater. A defeater is not merely disagreement. It is a consideration that, if true, would remove or weaken the support, or would show that the apparent support is misleading. Defeater screening is the discipline of identifying and facing such considerations rather than ignoring them.

Hinges are not reasons. Hinges are not hypotheses supported by evidence. They are background certainties that stand fast and make evidence, doubt, and correction possible in the first place.

Four uses of “certainty.” I distinguish subjective certainty (conviction), hinge certainty (bedrock), epistemic certainty (defeater resistant stability in practice), and absolute certainty (logical or moral necessity). When we disagree, it often helps to say which sense of certainty is in play.

Much of this is already written out, which is why I can respond quickly sometimes.

Optional sidebar: Hinges and Gödel, a structural parallel

A brief note for readers interested in foundations. In my paper I suggest a structural parallel between hinge certainties and Gödel style limits. The parallel is not evidential, and it is not a proof of anything in epistemology from mathematics. It is a comparison of structure.

In Gödel’s setting, once a formal system is rich enough, there are truths expressible within the system that cannot be proven by the system’s own resources, and consistency cannot be established from within in the strongest way one might want. The upshot is not that mathematics collapses, but that the practice operates with boundary conditions that are not resolved by the same methods the system makes possible.

In the hinge setting, justificatory practices also have stopping points. Certain things stand fast, not as conclusions of inquiry, but as the background that makes inquiry, doubt, evidence, and correction possible. The upshot is not that justification collapses, but that justification always operates within a framework whose role is not that of an ordinary claim awaiting ordinary support.

So the comparison is this: both domains exhibit limits on what can be achieved from within, and both continue rationally once those limits are acknowledged. That is all I mean by the parallel.

If you want to press on this, I would welcome it, but it will help to keep the debate focused on whether the analogy is illuminating rather than on technical details of Gödel’s proofs.

When I use the word “justification,” I am not talking about something private, a feeling of confidence, or a mere report of how things seem from a subjective point of view. I mean justificatory standing, the sort of standing a belief has when it is supported by the standards that govern a practice, standards for what counts as evidence, what counts as error, and what counts as correction. — Sam26

I've read all seven of your chapters. Just for workability, I'm going to respond to each chapter separately. This may mean that what I have to say will be a bit disjointed. We'll see.

My biggest overall issue--JTB generally applies to propositions but most of the knowledge we have and use is not really expressible in that form. As an engineer, I usually talked about "conceptual models," which means an overall picture of the situation--in my case it was real estate properties and the soil and groundwater characteristics distributed across the site and at different depths. Models like that will generally be judged and justified as accurate rather than true. As I indicated, as I see it, the way we use knowledge on a daily basis tends to be more like how I've described it rather than just the truth of propositions.

This is highlighted by your discussion of the idea of standards of practice which are used to justify truth. In general, I think that's right, but how standards are applied under JTB (or JTB-U) is different from how various practices apply their standards. How do I apply an engineering standard to a simple declarative statement?

So, I worry that I am going to send your discussion off on a tangent. Now that you've seen some of the substance of my thoughts, should I continue?

Also--I am not really familiar with Wittgenstein, so my comments will not be in terms of his way of seeing things.

I've read all seven of your chapters. Just for workability, I'm going to respond to each chapter separately. This may mean that what I have to say will be a bit disjointed. We'll see.

My biggest overall issue--JTB generally applies to propositions but most of the knowledge we have and use is not really expressible in that form. As an engineer, I usually talked about "conceptual models," which means an overall picture of the situation--in my case it was real estate properties and the soil and groundwater characteristics distributed across the site and at different depths. Models like that will generally be judged and justified as accurate rather than true. As I indicated, as I see it, the way we use knowledge on a daily basis tends to be more like how I've described it rather than just the truth of propositions.

This is highlighted by your discussion of the idea of standards of practice which are used to justify truth. In general, I think that's right, but how standards are applied under JTB (or JTB-U) is different from how various practices apply their standards. How do I apply an engineering standard to a simple declarative statement?

So, I worry that I am going to send your discussion off on a tangent. Now that you've seen some of the substance of my thoughts, should I continue? — T Clark

I don't think this is a tangent, I think it's exactly the kind of stress test that helps clarify my ideas.

On the first point, I agree that a great deal of what we rely on is not best described as a single proposition. Much of it is a competence, a grasp of a situation, a model, or a way of seeing how things hang together. In engineering, the object of assessment is often a conceptual model, and the operative question is whether the model is accurate, robust, and fit for use across the relevant conditions, not whether a sentence is true in isolation.

My reply is that this does not put the JTB family out of business, it forces a clarification of what “truth” and “justification” are doing. A model can be assessed for correctness in the world, it can succeed or fail, it can be refined under error signals, and it can be defeated by counterevidence. In other words, it has correctness conditions even if it's not naturally expressed as a single declarative statement. The “propositional” layer can be treated as a partial extraction from the model, for example, predictions, constraints, and consequences that can be checked. That is often how the model earns and keeps its standing.

On your second point, I agree that we should not imagine applying an engineering standard to an isolated declarative sentence as if that were the primary unit of knowledge. The better way to put it is that standards of practice govern the evaluation of the claim in its proper form, which may be a model, a procedure, a measurement protocol, or a forecast. When I say “public” or “practice-governed,” I mean that there are criteria for correct application, error, and correction that can be articulated and contested within the practice. Engineering seems like a textbook example of this, because the standards include calibration, measurement error, boundary conditions, sensitivity to assumptions, and the discipline of revising the model when it fails.

So, I would welcome you continuing, but with one focusing suggestion so we do not drift. When you respond to a post, pick one concrete engineering example of a conceptual model and say how it is justified in your sense. Then we can map it onto my vocabulary without forcing it into a single sentence: which route of justification is doing the work, what would count as a defeater, where No False Grounds shows up, and what “practice safety” looks like in that domain. If we can do that once, the “propositions versus models” worry will either dissolve or become precise enough to evaluate.

The “propositional” layer can be treated as a partial extraction from the model, for example, predictions, constraints, and consequences that can be checked. That is often how the model earns and keeps its standing. — Sam26

Yes, this is headed into the direction that I find most useful.

When you respond to a post, pick one concrete engineering example of a conceptual model and say how it is justified in your sense. Then we can map it onto my vocabulary without forcing it into a single sentence: — Sam26

Here is something I stole from a post I made a few years ago.

A site conceptual model is just a description, image of the site which lays out all the information gathered during the investigations. To me, the most useful way of presenting a SCM is visually, using figures. Data tables are also needed. There will also be calculations e.g. groundwater flow direction and velocity, contaminant degradation rates, averages. On the figures, you can show the locations of the sources of the contamination and how it has moved and is presently distributed across the site. You can also show the expected distribution of contamination in the future based on groundwater and fate and transport modelling. You can also show the locations of existing and potential human and environmental receptors.

Typical data points include boring logs; analytical results of soil, groundwater, and sediment samples; visual observation of site conditions; topographic and bathymetric surveys; geophysical surveys; and wetland surveys. Going deeper, there are assumptions associated with laboratory analytical methods. Which in particular are you talking about?

I’m going to be gone for a while

Really strong OP, thanks. I especially admire how you invite critique, even offering your own sense of the possible weak points for discussion.

There's a great deal of interest to comment on, but I'll start with something relatively simple, but important.

From post #3:

If justification is a standing within a practice, then understanding is the competence by which a person can genuinely participate in that practice, not merely mimic its conclusions. — Sam26

I think I've grasped how you use "understanding" here, and why it isn't a fourth criterion for knowledge, but rather an attempt to clarify what justification actually entails. At this point, an example would be helpful. The question of what it means to "mimic the conclusions" is central, I think. You write:

Someone can hold a true belief and even cite a correct supporting data, while still failing to grasp what that support is doing, what would count against it, what would defeat it, and what would count as a relevant correction. In that situation the belief can look justified from the outside, and even to the person themselves, but the justificatory standing is fragile, because the person does not reliably track the mistake-conditions that the practice treats as decisive. — Sam26

As an example, I picture a student who writes a paper on some topic in science; the paper describes a true belief which the student holds, and cites all the correct data. Why is the student only mimicking the conclusions? Because their understanding of why the data really do provide that support has to involve a simultaneous understanding of the conditions under which they wouldn't -- the defeaters, in other words. If the student lacks this understanding, their claim to justification is at best shaky, and probably false.

Does all that sound right? OK, here's the question: If the belief "looks justified" both from the outside (publicly) and to the person themselves (privately), how should we describe the process that will show us it is not justified? It seems as if a verification of understanding requires a further, dialogic process with the one who claims justification (and knowledge). And that's fine, but perhaps you should emphasize the need for this further step. I agree that it still doesn't make for a fourth criterion, but it does seem significantly different from the process we would engage in to learn a person's justifications -- which, as you point out, can be merely cited or mimicked. Another homely example might be defending a thesis.

Maybe all of this is to say we can't "vet understanding" in the same way we can vet a proof, or even a proposition. The proof doesn't reply to our questions, but we do require the person to, otherwise we're not in a position to say whether the U part of JTB+U is present. This doesn't contradict your theory in the slightest, just elaborates it a bit, and puts it in a context of Habermasian "communicative action."

If justification is a standing within a practice, then understanding is the competence by which a person can genuinely participate in that practice, not merely mimic its conclusions.
— Sam26

I think I've grasped how you use "understanding" here, and why it isn't a fourth criterion for knowledge, but rather an attempt to clarify what justification actually entails. At this point, an example would be helpful. The question of what it means to "mimic the conclusions" is central, I think. You write:

Someone can hold a true belief and even cite a correct supporting data, while still failing to grasp what that support is doing, what would count against it, what would defeat it, and what would count as a relevant correction. In that situation the belief can look justified from the outside, and even to the person themselves, but the justificatory standing is fragile, because the person does not reliably track the mistake-conditions that the practice treats as decisive.
— Sam26

As an example, I picture a student who writes a paper on a topic in science; the paper describes a true belief which the student holds, and cites all the correct data. Why is the student only mimicking the conclusions? Because their understanding of why the data provides a justification has to involve a simultaneous understanding of the conditions under which they wouldn't -- the defeaters, in other words. If the student lacks this understanding, their claim to justification is shaky, and probably false.

Does that sound right? OK, here's the question: If the belief "looks justified" both from the outside (publicly) and to the person themselves (privately), how should we describe the process that will show us it's not justified? It seems as if a verification of understanding requires a further, dialogic process with the one who claims justification (and knowledge). And that's fine, but perhaps you should emphasize the need for this further step. I agree that it still doesn't make for a fourth criterion, but it does seem significantly different from the process we would engage in to learn a person's justifications, which, as you point out, can be merely cited or mimicked. Another homely example might be defending a thesis.

Maybe all of this is to say we can't "vet understanding" in the same way we can vet a proof, or even a proposition. The proof doesn't reply to our questions, but we do require the person to, otherwise we're not in a position to say whether the U part of JTB+U is present. This doesn't contradict your theory in the slightest, just elaborates it a bit, and puts it in a context of Habermasian "communicative action." — J

This is a strong reading of what I meant, and your student example captures the central point. “Mimicking the conclusions” is precisely the case where a person can reproduce the correct outputs, cite the right data, and sound fluent, while lacking a grasp of the mistake conditions, the relevant defeaters, and the revision pathways that the practice treats as decisive. In that situation, the belief can look justified, even to competent observers, because the surface marks of justification are present, but the standing is fragile because it's not anchored in the competence that makes those marks responsibly usable.

Your question about how we show that the belief is not justified is also right, and it helps to make explicit something I left implicit. In many domains we do not vet understanding by inspecting a static artifact alone, as if it were a completed proof. We vet it by exposing the claimant to the practice’s tests, especially its countercases. That often does require a dialogic dimension: questions, challenges, requests for boundary conditions, requests for what would count as defeating information, and requests for how the claim would be revised if those defeaters obtained.

But I want to put this carefully, so it does not look like an added criterion. The “further step” you describe is not a separate requirement piled onto justification, it's one of the ordinary ways a practice determines whether a person has justificatory standing or has only borrowed it. It is the difference between an utterance that happens to be correct and a competence that can carry that correctness across the relevant cases. In that sense, the dialogic process is a method of assessment, not an additional condition of knowledge.

It is also worth noting that the need for dialogue varies by context. Sometimes understanding can be vetted through performance without explicit conversation, for example by reliable error detection, appropriate revision under new data, or correct handling of nearby cases. In other settings the quickest test is indeed oral examination, thesis defense, or cross examination. Either way, the underlying point is the same: understanding is shown in how the claimant navigates defeaters, boundary conditions, and correction, not merely in the ability to cite supporting considerations.

So, I agree with your closing line as an elaboration: we cannot vet understanding in the same way we vet a proof considered as a static object. We vet it by putting the claimant into the space of questions and challenges that the practice treats as intelligible. That is compatible with my view, and I think it helps readers see that “public” does not mean “a pile of citations,” it means susceptibility to the practice’s checks, including dialogic ones when the case calls for it.

If you want a single sentence version of the answer: when a belief looks justified on the surface, the practice distinguishes genuine standing from mimicry by testing whether the person can track defeaters and revise under correction, and that test is often, though not always, dialogic.

Here is something I stole from a post I made a few years ago.

A site conceptual model is just a description, image of the site which lays out all the information gathered during the investigations. To me, the most useful way of presenting a SCM is visually, using figures. Data tables are also needed. There will also be calculations e.g. groundwater flow direction and velocity, contaminant degradation rates, averages. On the figures, you can show the locations of the sources of the contamination and how it has moved and is presently distributed across the site. You can also show the expected distribution of contamination in the future based on groundwater and fate and transport modelling. You can also show the locations of existing and potential human and environmental receptors.

Typical data points include boring logs; analytical results of soil, groundwater, and sediment samples; visual observation of site conditions; topographic and bathymetric surveys; geophysical surveys; and wetland surveys. Going deeper, there are assumptions associated with laboratory analytical methods. Which in particular are you talking about? — T Clark

This is what I had in mind. A site conceptual model is a perfect case of knowledge that is not best expressed as a single proposition, but as an integrated representation: figures, tables, calculations, assumptions, and forecasts. In my terms, the unit being assessed is not one sentence but a model with correctness conditions, it can be more or less accurate, it can succeed or fail under error signals, and it can be revised when it runs into defeaters.

So, when I talk about justification here, I am not asking you to apply an engineering standard to a bare declarative sentence. I am asking how the SCM earns and keeps justificatory standing in the practice. Your description already points to the routes: sensory observation at the site, measurement and sampling, inference and modelling, testimony in the form of reports and lab results, and linguistic training in the way standards and classifications are applied. The important question is how those routes are disciplined.

That is where the guardrails map cleanly:

No False Grounds: what would count as a false ground in the SCM, a faulty assumption or input that is doing decisive work, for example a mistaken stratigraphic interpretation, a mislocated source term, or an analytical artifact that propagates through the map of contamination.

Practice Safety: what makes the SCM robust rather than lucky, for example triangulation across independent data types, sensitivity checks, conservative assumptions where appropriate, and repeated checks that would expose a fragile inference.

Defeater Screening: what kinds of findings would force revision, for example a new boring log that contradicts the stratigraphy, a plume boundary that violates the predicted hydraulic gradient, or receptor evidence inconsistent with the proposed pathway.

On your last question, I am not asking about one laboratory method in the abstract. I mean the assumptions that bear the weight in the overall chain that supports the SCM.

When I use the word “justification,” I am not talking about something private, a feeling of confidence, or a mere report of how things seem from a subjective point of view. I mean justificatory standing, the sort of standing a belief has when it is supported by the standards that govern a practice, standards for what counts as evidence, what counts as error, and what counts as correction. — Sam26

So you mean Doxa?

When I use the word “justification,” I am not talking about something private, a feeling of confidence, or a mere report of how things seem from a subjective point of view. I mean justificatory standing, the sort of standing a belief has when it is supported by the standards that govern a practice, standards for what counts as evidence, what counts as error, and what counts as correction.
— Sam26

So you mean Doxa? — Alexander Hine

Not doxa in the pejorative sense of mere opinion. I mean the normative standing a belief has when it is entitled by the standards of evidence and correction that govern a practice.