EDIT: I agree that it isn't possible to claim 1 without also claiming 2, and vice versa. Perhaps that's all you mean by "Why not both?" If so, it's fine. — J

I’m trying to leave the forum for now. But, yes, claim 1 and claim 2 are semantically the same (with a possible semantic difference regarding emphasis). As to “why not both?” I gave an overview for why both will need to occur for JTB knowledge to obtain. Someone who is steadfastly certain in their belief that X (is true) without having any reason to believe it (this being synonymous with not having any justification for it) … ought to be trusted to in fact know what they’re talking about? If this were so, then, heck, planet Earth must be hollow and inhabited by sapient beings living in paradise. This then being a factual truth because others are so certain of it. I’ve encountered such. As to differing forms of knowledge, again, the knowledge-by-acquaintance and knowledge-by-JTB dichotomy I’ve previously mentioned showcases this. The first is had devoid of conscious belief; one doesn’t believe that one is seeing green grass but simply so does (and thereby knows one does, this in the knowledge by acquaintance sense of knowledge and not the JTB sense). But once belief is introduced, it must be both true and one must have (valid) reason for believing it so in order to count as knowledge. Some people want all knows to have the strength of knowledge-by-acquaintance. We can dream away all we like, but that is not the nature of the reality we’re living in. Else, again, the planet must then be hollow.

Thermometers never commit epistemic errors; they can only mislead those who uncritically rely upon them. Likewise, the same can be said of a 'believer's' utterances.

The dilemma is either

A. a belief merely refers to the coexistence of a believer's mental state and an external truth-maker, where the external truth-maker is decided by the linguistic community rather than the believer. In which case the intentionality associated with the believer's mental state is irrelevant with respect to the belief that the community ascribes to the believer as a matter of linguistic convention rather than of neurological fact.

or

B. Beliefs refer to the actual physical causes of the believer's mental-state - in which case the believer's intentionality is relevant - so much so, that it is epistemically impossible for the believer to have false beliefs. (Trivialism). — sime

The situation isn't different with humans as measuring devices. And hence as with the example of a thermometer, either humans have intentional belief states, in which case their beliefs cannot be false due to the object of their beliefs being whatever caused their beliefs, else their beliefs are permitted to be false, in which case the truthmaker of their belief is decided externally by their community. — sime

So we have two distinct notions of truth in play: Intersubjective mathematical truth... versus what we might call "John's subjective truth"... — sime

Consider this post a bookmark, as I have been wanting to respond to these posts but haven't had the time and am now occupied again.

I think there are false dilemmas occurring here, owing to a presupposition that can hopefully be explored later on, but which is close to the presupposition that "the situation isn't different with humans as measuring devices."

The key will be to see that one's truthmaker is not stipulated merely by oneself, and that the truthmaker is not merely a consensus reached by an external community. For the realist there is an object that exists in reality which one is trying to understand, and correctly understanding the object will not be a matter of aligning oneself with any particular linguistic community. In a more preliminary way we would want to ask why the dichotomy you present would be plausible. Why think that the two options you present are exhaustive?

@Banno@Janus@Count Timothy von Icarus @Ludwig V @Sam26
Thanks, and coincidentally, I also have to be offline for 2 weeks, as I'm going out of the country. Appreciate the conversation and look forward to chatting with everyone when I get back.

Right, and to restate my point, J's objection holds against any theory of knowledge which takes truth to be a necessary condition of knowledge, and this is not just JTB, it is pretty much every theory of knowledge. — Leontiskos

I am not sure about that implication of what J has been arguing, but I think truth is a necessary condition of knowledge, — Janus

@J's central move is to say that if someone thinks truth is a necessary condition of knowledge, then they must explain how truth can be known apart from all the other conditions of knowledge (such as justification or belief), and since no one can do that, therefore truth is not a necessary condition of knowledge. This is endlessly confused.

and I also think knowing the truth and knowing how you know it is also a necessary condition of knowledge. That said, I am not claiming that we cannot think we have knowledge and yet be wrong. — Janus

Okay.

I will just link to , particularly the second half. If someone thinks this:

The problem, as I pointed out earlier, is that if we don't know whether the justifications for our beliefs are themselves [sound] then [...] How do we know they are adequate as justifications? — Janus

...Then they are making justification into something other than justification. Justification is per se persuasive. Persuasiveness isn't something that gets tacked onto justification. A false justification is something that purports to be persuasive but is not. The question of how we know whether a justification is adequate has to do with logic, inference, validity, etc., and goes back to what about "the Aristotelian way to develop such an idea."

(Still, even once we understand how soundness pertains to justification, there remains a difference between the concept of soundness and the concept of truth. They do not collapse into each other even in those cases where they are biconditional.)

Edit: Part of the problem here is the semantic range of the word "justification." Properly speaking, what is needed for the internalism that is being presupposed is for one to have the explanation (aitia) for why something in reality is the way it is. One must be able to (correctly) explain why it is true. "Justification" can mean that, but it can also mean providing an ad hoc or unsound account, and the critiques of a justification condition are presupposing this latter meaning (of faux justification).

Isn't understanding the same thing as justification? I'm not sure what the U adds to JTB, given that we assess understanding in terms of justifications.

As for deciding whether a refutation is valid or not, this rests upon the truth of one's auxiliary hypotheses. So unless those can also be tested, one cannot know whether the refutation is valid, which is the staple criticism of Popper's falsificationism - that individual hypotheses are impossible to test, since their validity stands and falls with the truth of every other hypothesis. So the bridge from practical refutation in everyday life, which often involves the testing of individual hypotheses under the assumption of true auxilliary hypotheses, doesn't withstand skeptical scrutinty and the standards demanded by scientific epistemology - an essentially unattainable standard, relegating JTB to the realm of the impossible, or to the realm of semantics that is epistemically vacuous. — sime

On the first point: understanding is not the same as justification. Justification is the giving of reasons that satisfy the standards of a language-game. Understanding is a matter of concept-mastery, the ability to use terms correctly within that grammar. A student can repeat reasons in a way that looks justified, but without grasping the concepts, they do not understand—and so they don’t know. The “+U” is needed because justification can sometimes be mimicked or borrowed without genuine uptake.

On the second point: you are right that Popper’s falsificationism raised the problem of auxiliary hypotheses, and that one cannot isolate hypotheses absolutely. But this does not mean that knowledge is impossible. It means that justification is corrigible and practice-bound. When we test a claim, we do so against a backdrop of hinges and auxiliary commitments. If anomalies arise, we do not simply abandon the claim, but we check whether the defeater is genuine. This is why defeater-screening is part of the JTB+U framework.

The skeptical worry that this makes JTB impossible arises from a mistaken demand: that justification must be final and immune to revision. Wittgenstein helps us dissolve that demand. Knowledge does not require absolute independence from auxiliary assumptions; it requires that our reasons hold up against available defeaters in the practices that give those reasons sense. Here the distinction is crucial: the JTB framework itself—truth, belief, justification (+U)—remains the definition of what knowledge is. But our application of that framework in practice is fallible. We can misidentify truths, we can mistake apparent reasons for genuine justification, and we can claim understanding where only parroting exists. The framework is sound; what fails is our use of it.

So the linkage is this: justification is public and corrigible, understanding is the uptake that prevents mere parroting, and truth remains the non-negotiable condition. Together, they let us say that knowledge is possible without pretending that justification must ever be perfect or final. Our judgments may fall short, but that is an error of application, not a defect in the framework itself.

Right, but if you cannot be sure that you have true beliefs now why should you trust your own beliefs about the long term trend of knowledge or epistemology more generally?



:up:

I am interested though, since you recommended a Bayesian approach, how you think they are able to deal with the problems of selection narratives. The structure of BT by itself does not seem to get around the problem that fitness vis-á-vis reproduction/survival does not seem to necessarily track with truth.

Right, but if you cannot be sure that you have true beliefs now why should you trust your own beliefs about the long term trend of knowledge or epistemology more generally? — Count Timothy von Icarus

That question rests on a misunderstanding of what knowledge is. It assumes that unless I can be sure of my beliefs in the sense of absolute, indubitable certainty, then I have no rational grounds for trusting them. But knowledge has never required that kind of infallibility. On JTB+U, knowledge requires truth, belief, justification, and understanding. Those conditions are demanding, but they do not amount to immunity from error.

Part of the confusion here comes from how we use the word certainty. It can mean at least three different things. First, there is subjective certainty, the psychological feeling that I cannot be wrong. That is fallible, since I can feel certain and yet be mistaken. Second, there is objective certainty, the hinge-level background we do not doubt—like that the world has existed for a long time. These certainties are not proved but stand fast as the conditions of doubt and knowledge alike. Third, there is epistemic certainty, where a claim is true and justified to the point that doubt has no footing within a given practice. Even this form of certainty remains corrigible if new defeaters arise.

The challenge you raise trades on conflating these senses. It assumes that unless I can have absolute, infallible certainty, I cannot call my beliefs knowledge or trust them for long-term reflection. But this is simply not what knowing is. Knowledge, on the JTB+U account, is defeasible but real: I can hold a belief that is true, justified in my practice, and conceptually understood, even though I remain open to correction.

So why trust my beliefs now, including beliefs about epistemology? Because they have withstood defeater screening across the routes of justification available to me: testimony, reasoning, sensory experience, linguistic clarity, and logical consistency. If new defeaters arise, I will adjust. But until then, the best explanation for their stability is that they are tethered to truth.

The upshot is that skepticism here demands the wrong thing. It asks for absolute certainty, when what knowledge actually requires is justified, true, and understood belief within our forms of life. To see that distinction is to dissolve the challenge.

Because they have withstood defeater screening across the routes of justification available to me: testimony, reasoning, sensory experience, linguistic clarity, and logical consistency. If new defeaters arise, I will adjust. But until then, the best explanation for their stability is that they are tethered to truth — Sam26

But you have already allowed that cultural-historical regressions might lead to a case where a culture widely accepts that a true idea/theory has been "defeated" when it hasn't been. How do you know that you're not in that situation?

The move of: "scholasticism lost ground because it was properly defeated, but if secular naturalism and exclusive humanism lose acceptance that will be simply a regression," seems arbitrary unless you can show why some beliefs are actually true and cannot be the result of regression/error. That is, an apparent defeater or error is not solid evidence that a theory/idea is actually wrong, since you have already allowed that whole cultures can misidentify defeaters and errors for long periods.

But you have already allowed that cultural-historical regressions might lead to a case where a culture widely accepts that a true idea/theory has been "defeated" when it hasn't been. How do you know that you're not in that situation?

The move of: "scholasticism lost ground because it was properly defeated, but if secular naturalism and exclusive humanism lose acceptance that will be simply a regression," seems arbitrary unless you can show why some beliefs are actually true and cannot be the result of regression/error. That is, an apparent defeater or error is not solid evidence that a theory/idea is actually wrong, since you have already allowed that whole cultures can misidentify defeaters and errors for long periods. — Count Timothy von Icarus

That is the way some pushback on this idea, but I think the apparent arbitrariness disappears once we distinguish between (a) the framework for knowledge and (b) our fallible application of it. There is always a difference between what I think counts as knowledge and what really is knowledge. Gettier cases make this clear: someone thinks they are justified, but the justification is defective, so they do not actually know. The same thing can happen at the cultural level—whole societies can misidentify defeaters or mistake regression for progress. That does not show that knowledge is impossible; it shows that our application of JTB+U can go wrong. The framework itself—truth, belief, justification, and understanding—remains intact. What fails is our judgment, our recognition of what counts as a genuine defeater.

So how do we avoid arbitrariness? By keeping the distinction clear between apparent defeaters and genuine defeaters. An apparent defeater is what a culture or individual takes to undermine a claim at a given moment. A genuine defeater is one that endures across error-signals, survives cross-checking through multiple justificatory routes, and holds up under defeater screening in the long run. Misfires don’t erase the difference between appearance and reality; they only show that human uptake often lags behind truth.

This is why I say Scholasticism lost ground for reasons that were not merely political or sociological. Its justificatory practices proved less able to handle new error-signals. If secular naturalism were later abandoned, the question would not be settled by its decline in popularity or survival-value but by whether the reasons against it genuinely exposed its falsity. To decide that requires the same thing JTB+U always requires: truth, belief, justification, and understanding tested against defeaters.

The risk of cultural error is real, but that does not make all judgments arbitrary. It means we must hold our claims with epistemic humility, open to correction, but not collapsing into relativism. Some beliefs are true and will survive defeater screening indefinitely (mathematical truths, some moral absolutes). Others are corrigible. What matters is whether our justificatory practices are strong enough to keep those differences visible.

For JTB+U to be viable as a framework, it has to work more often than not. If the framework only rarely connected belief with truth, it would collapse into skepticism or relativism. But the very fact that our practices of knowing guide us successfully in daily life, science, history, and moral reasoning shows that it does work.

We navigate the world, build functioning technology, diagnose illnesses, and correct one another’s errors. These are not flukes. They demonstrate that justification, when tethered to practice and subjected to defeater screening, is in fact truth-conducive. Understanding ensures that justification is not merely parroted but conceptually grasped. This combination makes it more likely than not that our beliefs line up with reality.

Of course, mistakes and regressions happen, both individually and culturally. But if error dominated, the very concepts of knowledge and justification would lose their grip. The fact that we can identify mistakes as mistakes already shows the framework is working. Our ability to mark regressions as regressions depends on having a more stable body of truths against which those failures stand out.

So, JTB+U is viable because it works in practice most of the time. Its fallibility is not a weakness but a strength: it builds in the possibility of correction without demanding infallibility. What matters is that the framework links belief, justification, and understanding to truth with enough reliability to sustain our practices of inquiry, correction, and progress.

Error is the thing that makes knowledge possible. This is counterintuitive.

Imagine you're inhabiting a character in a dream who is running from the mafia. You're hiding in a cabin in North Dakota, but a man enters your dwelling and you know he's there to kill you.

The concept of knowledge is in play here, and it mostly signifies confidence. It's just turbo-charged belief.

It wouldn't make sense to say it's an opinion, because the mafia threat isn't a matter of opinion. It wouldn't make sense to say the character knows it, but it's not true. So we could add on truth.

I did kill the guy in the dream. I didn't have any choice.

It wouldn't make sense to say it's an opinion, because the mafia threat isn't a matter of opinion. It wouldn't make sense to say the character knows it, but it's not true. So we could add on truth. — frank

It makes sense to say the man thinks he knows, but he doesn’t. This is something we see all the time: people confuse what they believe with what they actually know. The key difference is that conviction alone isn’t knowledge, and sometimes the evidence that seems to support a belief doesn’t really justify it.

It makes sense to say the man thinks he knows, but he doesn’t. This is something we see all the time: people confuse what they believe with what they actually know. The key difference is that conviction alone isn’t knowledge, and sometimes the evidence that seems to support a belief doesn’t really justify it. — Sam26

I don't think your conception of knowledge is going to stand up to a skeptical challenge. At any time, we may be mistaken about our justifications. So, to nail the jello to the wall, how do you determine if the evidence in front of you is sufficient for knowledge? I say you have no way to do that. You only use the word "knowledge" to signify confidence in your beliefs.

A side issue is that I knew the man was there to kill me because I created the dream specifically to confront certain fears. I knew he was there to kill me in the same way I know the bishop goes diagonally. Life is frequently like this, but realizing this requires grasping the extent to which we live in our own dreams.

I don't think your conception of knowledge is going to stand up to a skeptical challenge. At any time, we may be mistaken about our justifications. So, to nail the jello to the wall, how do you determine if the evidence in front of you is sufficient for knowledge? I say you have no way to do that. You only use the word "knowledge" to signify confidence in your beliefs. — frank

If knowledge is just confidence in one's belief, then one's confidence/conviction that one knows would suffice, that can't be correct. Sure, we can be mistaken in what we think justifies our belief, but as I pointed out earlier that doesn't justify being skeptical about JTB. Your skepticism is unfounded, you seem to think that if we can't know in an absolute sense, then we can't have knowledge (at least in the sense that I'm proposing). We don't use the concept knowledge,generally, in the way you seem to think. Even in science our conclusions are mostly probable.

In the last three pages I explained this in detail.

If knowledge is just confidence in one's belief, then one's confidence/conviction that one knows would suffice, that can't be correct. — Sam26

I didn't say knowledge is confidence in one's belief. I said we use the word to express that we're confident. The reasons for that confidence vary.

Instead of trying to provide a definition for knowledge, think about how the word is used. The next time you catch yourself using the word, stop and reflect on what you're trying to convey.

Instead of trying to provide a definition for knowledge, think about how the word is used. The next time you catch yourself using the word, stop and reflect on what you're trying to convey. — frank

If this is what you think I'm doing, then you haven't understood anything I've said. My impression @frank is that you haven't read my posts in the last few pages, because if you had, you would know how foolish your remark is.

It may be objected that nothing truly novel is added by the ‘+U.’ Some have held that unless a person grasps the concepts at work, their justification is not genuine to begin with. In that sense, understanding has always been latent in the J-condition. My argument is not that I am introducing an alien element, but that by making U explicit we secure what has too often been assumed in silence. Once drawn into the open, the requirement of understanding keeps us from mistaking parroting for uptake, appearance for reality, or borrowed reasons for genuine justification. If the condition seems obvious, that is precisely the point: it has always been there, but left unnamed, it has allowed too much misdescription to slip through.

Possibly I also haven't been clear about why the PoV matters -- who is doing all this. The phrase "point to" is meant to raise this question. — J

You are right. It makes a lot of difference what the context is. My apologies if someone else has responded while I've been away.

I think you've been assuming, in this discussion, that a single person is taking all these steps, but there's nothing in JTB that requires that. We don't ask, "Have I verified that this sentence is true?" but rather "Is this sentence true?"; we don't ask "Have I provided good justifications?" but rather "Are there good justifications?" — J

JTB amounts to a procedure for working out whether some random belief is actually knowledge. It's not exactly a discovery procedure for knowledge, because the belief needs to be given - unless it is actually a hypothesis.
If the random belief is someone else's claim to knowledge (and perhaps, in a way, all one's beliefs are claims to knowledge, if they are beliefs without qualification). The JTB makes most sense if we suppose that someone (A) is evaluating someone else's (B) belief that P. Then, (1) the justification needs to be B's justification. (2) P needs to be true. (3) ex hypothesi the belief is B's belief.
What seems odd at first sight is that, if A goes through all of these steps and accepts them, A knows that p. But I don't think that is a bug. I think that it is a feature. It should not be surprising that members of a social group have ways of sharing information. If we didn't have such a system, we would almost certainly invent it.
I don't think it is circular, but it does presuppose that, to put it this way, A needs to be qualified to carry out such an evaluation, that is, needs to understand the relevant proposition in its linguistic and epistemic context, which means that A needs to be competent in the relevant skills. The same applies to B. I think this observation picks up the idea of understanding.
When the justification in question is conclusive, the T clause is otiose. When the T clause is false, the J clause is otiose.
It is unfortunate that the format here makes it difficult to emphasize that propositions cannot be considered individually, as if they were atoms. They are always part of a system..

JTB wants to pin down the correct use of "I know"; I'm suggesting that it might be more profitable to look at the ways we actually use "I know." I don't think they correspond to JTB. There are many things I believe I know, but am not certain they are true. JTB would argue that, therefore, I'm using "know" incorrectly. Whereas I'm saying that it's JTB that needs correction, not me. This latter position lacks punch, of course, unless the "me" can be turned into "us" with sufficient frequency. We need a fairly widespread agreement on the faults of JTB in order to claim that it doesn't capture our common practice. — J

I'm all for paying attention to how "know" is actually used. But it may not be easy to discern a single, consistent use, or uses may be different in different contexts. There are some common uses of "know" that, I think, philosophy needs to discount. If I place a bet on an outsider in a race, and exclaim "I knew it would win", it is a rhetorical use of little interest to philosophy. At most it expresses the subjective certainty of the speaker. I don't see that little tidying up for philosophical purposes would go amiss.
I do think that there is fairly widespread agreement that it is surprisingly hard to formulate a generally acceptable articulation of JTB. If someone could come up with a reasonably acceptable alternative - and perhaps the view that "know" is a primitive term is one such - I would expect it to attract support.

So the bridge from practical refutation in everyday life, which often involves the testing of individual hypotheses under the assumption of true auxilliary hypotheses, doesn't withstand skeptical scrutinty and the standards demanded by scientific epistemology - an essentially unattainable standard, relegating JTB to the realm of the impossible, or to the realm of semantics that is epistemically vacuous. — sime

OK. So what's your alternative?

On the first point: understanding is not the same as justification. Justification is the giving of reasons that satisfy the standards of a language-game. Understanding is a matter of concept-mastery, the ability to use terms correctly within that grammar. A student can repeat reasons in a way that looks justified, but without grasping the concepts, they do not understand—and so they don’t know. The “+U” is needed because justification can sometimes be mimicked or borrowed without genuine uptake. — Sam26

Adding another clause to JTB just to ruling out mimicking or parroting seems a bit over the top. What is much more important is to recognize the importance of the competence of the knower, as you do, of course.

The framework is sound; what fails is our use of it. — Sam26

Well, I would agree that we presuppose that the framework is sound. But I don't think they are necessarily set in stone and they may need to be modified.

The structure of BT by itself does not seem to get around the problem that fitness vis-á-vis reproduction/survival does not seem to necessarily track with truth. — Count Timothy von Icarus

Perhaps not. But if truth was not at least compatible with reproduction and survival, we would surely abandon it or die out. Though some events in the world make me wonder whether that is the case and how committed most people are to truth. Perhaps truth is not as important as we philosophers like to think it is.

JTB amounts to a procedure for working out whether some random belief is actually knowledge. — Ludwig V

I think it's just an expression of one of the meanings of "knowledge."

.Then they are making justification into something other than justification. Justification is per se persuasive. Persuasiveness isn't something that gets tacked onto justification. A false justification is something that purports to be persuasive but is not. The question of how we know whether a justification is adequate has to do with logic, inference, validity, etc., and goes back to what ↪I said about "the Aristotelian way to develop such an idea." — Leontiskos

To be persuaded is no guarantee of the soundness of what has done the persuading. I just don't see how the truths or falsities that constitute a purported justification for some belief can be irrelevant. You yourself say that a "false justification is something that purports to be persuasive but is not", which seems to agree with what I just said. Although the "purports to be persuasive" seems wrong, inapt since people are often persuaded by falsities. I would change the "persuasive" there to 'true'.

I think it's just an expression of one of the meanings of "knowledge." — frank

Yep, there are at least a few others.

I think it's just an expression of one of the meanings of "knowledge." — frank

OK. Then can you tell me anything about the other meanings?

OK. Then can you tell me anything about the other meanings? — Ludwig V

There's know that and there's know how. Sometimes it's know of. In some cases, it might be a combination?

I know how you feel.
You should know better than to eat wild mushrooms.
I didn't know which path I should take.
I want to know what it's like to jump from an airplane.
How do the migrating butterflies know the way to Mexico?
I love you more than you'll ever know.
Frank doesn't know his ass from a hole in the ground.

I don't think it's really necessary to build a formula for each usage. Do you?

There's know that and there's know how. Sometimes it's know of. In some cases, it might be a combination?

I know how you feel.
You should know better than to eat wild mushrooms.
I didn't know which path I should take.
I want to know what it's like to jump from an airplane.
How do the migrating butterflies know the way to Mexico?
I love you more than you'll ever know.
Frank doesn't know his ass from a hole in the ground. — frank

If I say “I know how you feel because I too have lost a parent”, then the structure does fit JTB:

Truth: it is true that I have felt grief of that sort.

Belief: I believe that what I experienced is relevantly similar to what you are feeling.

Justification: I can give reasons (describing my past emotions, circumstances).

Understanding (U): I actually grasp what fear, grief, or joy feels like from the inside.

Here the claim is epistemic — a propositional one: “Your feeling is of type F, and I have also experienced type F.” That does fall within JTB+U, though it is grounded in testimonial and experiential justification rather than inference or measurement.

By contrast, when it’s used loosely (“I know how you feel” as mere reassurance), it slips into the convictional/expressive use Wittgenstein noted — no propositional claim is really being advanced.

So: this phrase actually shows how the same sentence can belong to different language-games depending on how it is meant. Sometimes it’s epistemic (anchored in truth, belief, justification, and understanding); other times it’s expressive (an act of sympathy).

“You should know better than to eat wild mushrooms.”
Here “know” means having the practical awareness or standing knowledge of a danger. It presupposes JTB in the background (“these mushrooms are poisonous”), but the utterance functions as rebuke, not as a truth-claim.

“I didn’t know which path I should take.”
Epistemic use: this is propositional knowledge — lack of knowledge about which option is correct. It fits the JTB structure directly (truth of which path is best, belief about it, justification for choosing).

“I want to know what it’s like to jump from an airplane.”
This is a case of experiential knowledge (“knowledge by acquaintance”). It’s outside JTB’s domain, which focuses on propositional knowledge.

“How do the migrating butterflies know the way to Mexico?”
Here “know” is metaphorical. Butterflies don’t form justified beliefs. It’s a shorthand for innate mechanisms or instinct. Not JTB.

“I love you more than you’ll ever know.”
Purely expressive. “Know” here means “imagine” or “comprehend.” It’s not epistemic at all.

“Frank doesn’t know his ass from a hole in the ground.”
Colloquial. It means “Frank lacks competence.” It’s not propositional knowledge but a judgment of practical incompetence.

Knowing that → propositional knowledge, the domain of JTB (and your JTB+U). It’s about truth-evaluable claims: knowing that the train leaves at noon, that water boils at 100°C, that a promise was broken.

Knowing how → practical or skill knowledge. It’s about abilities or competences: knowing how to ride a bike, how to play the violin, how to fix a sink. This is not easily reducible to propositional form. Gilbert Ryle made this point sharply in The Concept of Mind: “knowing how” is not just a set of facts one has memorized but an ability to act appropriately.

That said, the boundary isn’t always rigid:

When someone says “I know how to ride a bike,” what they’re really claiming is competence in a practice — which is different from holding a justified true belief.

But “knowing how” often presupposes some propositional knowledge (e.g., knowing that you must balance, pedal, and steer).

Conversely, “knowing that” is often reinforced by “knowing how” (a surgeon who knows that a procedure requires precision must also know how to carry it out).

In my framework:

JTB+U is designed to cover knowing that — propositional knowledge.

Knowing how is better understood as a different language-game of “know”: one rooted in practice and skill rather than truth-apt propositions.

The two overlap in that “knowing how” can feed into propositional knowledge (e.g., an expert mechanic has knowledge-that cars behave in certain ways, because he knows-how to fix them).

JTB is fits into many different language-games, and the definition is based on Wittgenstein's family resemblance idea.

:up:

In agreement with much of your post.

To come at this from my own perspectives, in the examples frank provided I only see three differing types, or species, of consciously held knowledge addressed:

-- Knowing-that, which seems to always be knowledge-via-JTB.

-- Knowing-how, which I find is one subset of the more generalized category of knowledge-via-understanding (which I take can slightly bifurcate so as to apply both to conscious apprehensions as well as to consciously engaged in behaviors). Examples of this species of knowledge include: knowing (consciously understanding) the meaning of (e.g., of a word); knowing (behaviorally understanding) how to catch a ball; knowing (consciously understanding) another’s motive(s) and thereby knowing the other in this regard (i.e., holding a conscious understanding of who or what the other is); and the more philosophically renowned “know (consciously understand) oneself (as in: consciously understand what oneself as being is)”. This is what to me the butterfly question, for one example, would most likely addresses: how does a butterfly (granting it is in some way sentient even though not sapient) behaviorally understand how to navigate their way toward Mexico. Yes, many a conscious understanding can of course be justified, but an understanding is not quite a belief, being instead that upon which all beliefs are founded.

And, as your JTB+U maybe indirectly specifies, knowledge by understanding can be an utterly different beast in comparison to knowledge by JTB. For one example, one may not know (consciously understand) how to justify that which one knows via understanding (e.g., one’s knowledge via understanding of what is/being is) much less know (understand) how to convey it via words to oneself or to others. Even so, one’s known via understanding nevertheless so remains a known via understanding (e.g. no competent adult can claim with a straight face not to know/understand what is/being is, certain US presidents aside, even though we’re all at a loss for how to define it). Same with any skill one knows how to put to use so as to accomplish some end (and thereby behaviorally understands how to put to use so as to accomplish some end). Knowing (behaviorally understanding) how to ride a bicycle as an example of this. And, maybe needless to add, many an understanding can be non-conscious: e.g., someone with amnesia that discovers they yet know / behaviorally understands how to play piano, although they did not know (hold knowledge-by-acquaintance) that they so knew / behaviorally understood. Same could then be theoretically said of an amnesiac not knowing by acquaintance that they know by understanding what a complex scientific theory signifies (e.g., the theory of relativity or the theory of evolution) until coaxed into providing answers to certain theory-related problems. And “A doesn’t know his ass from a hole in the ground” is basically stating that A lacks satisfactory discernment (which is just saying that A lacks knowledge-by-understanding regarding differences which are otherwise commonly understood). Aldous Huxley’s Knowledge and Understanding gives some great insights into the uniqueness of understanding. For example,

[JTB type of] Knowledge is always in terms of concepts and can be passed on by means of words or other symbols. Understanding is not conceptual, and therefore cannot be passed on. It is an immediate experience, and immediate experience can only be talked about (very inadequately), never shared. — https://www.anthologialitt.com/post/aldous-huxley

-- All other provided examples to me consist of knowledge-by-acquaintance, of which knowing-of is a subset. An example of this type of knowledge I haven’t yet mentioned in the thread is that when one as a consciousness (aka, as a conscious being) is X, one as a consciousness knows this via a non-dualistic form of knowledge-by-acquaintance regarding oneself as consciousness: e.g., when one is angry, tired, sad, joyous, pleased, confident, in pain, etc., one knows one is so via direct and non-dual acquaintance with one’s one state of conscious being (such that there is no distinction between the subject of awareness (oneself) and its object of awareness (one’s momentary state of being)). Here, “to know” and “to be aware of” can be fully interchangeable expressions of the same. Hence, for example, knowing (being aware of) what it feels like to X. Or, “I love you more than you’ll ever know (i.e., more than you’ll ever be aware of)”.

At any rate, I again so far can only discern three types of knowledge in the examples provided: 1) knowledge by JTB, 2) knowledge by understanding, and 3) knowledge by acquaintance.

And I agree that the three can easily become, at least at times, indiscernibly entwined. This can, again, for example jive with your proposal of JTB+U (to which could also be technically added “+ knowledge by acquaintance”, for nothing can be otherwise known in the compete absence of any awareness, and all instances of awareness grant some form of knowledge by acquaintance, such as in what beliefs one upholds).

But my main reason for coming back to the forum to post this post is as follows:

I’m very curious to see if anyone can discern any other species of knowledge via the way “to know” is used within language that would not fit into any of the three categories just mentioned. (I haven’t yet found any.)

We don’t need epistemology to know; epistemology is an after-the-fact rationalization of what life already does. Epistemology is like a priest arriving after the festival, declaring rules for the dancing that already happened.

We knew long before we invented epistemology. Epistemology is only the fevered dream of a mind that cannot trust its own eyes, its own blood, its own joy.

Epistemology is a conceptual retrojection. Epistemology is the dualistic philosopher’s revenge on life: he invents rules for knowing after the fact, then declares life itself illegitimate without them.

There's know that and there's know how. Sometimes it's know of. In some cases, it might be a combination?

I know how you feel.
You should know better than to eat wild mushrooms.
I didn't know which path I should take.
I want to know what it's like to jump from an airplane.
How do the migrating butterflies know the way to Mexico?
I love you more than you'll ever know.
Frank doesn't know his ass from a hole in the ground.

I don't think it's really necessary to build a formula for each usage. Do you? — frank

Of course, there's "know that .." and "know how ..". I'm not sure about "know of..". Perhaps knowledge by acquaintance as well?
Whether you want a formula or not for each of your examples probably depends on how much store you put on them. I wouldn't necessarily want to set up a different kind of knowledge for each of your examples. Knowledge applies in a wide variety of language games and we can expect its definition to be adjusted to suit each context. Still "I know how you feel" is clearly different from "I want to know what it's like to jump from an airplane" and "I love you more than you'll ever know". All of them are different from "I know when it is high tide".

We don’t need epistemology to know; epistemology is an after-the-fact rationalization of what life already does. Epistemology is like a priest arriving after the festival, declaring rules for the dancing that already happened. — DifferentiatingEgg

Yes. I can see that you are sceptical about the point of philosophy and it is indeed doubtful. However, rationalizing what life already does is what philosophy does best, it is does anything at all. Compare Augustine on time.

This is what to me the butterfly question, for one example, would most likely addresses: how does a butterfly (granting it is in some way sentient even though not sapient) behaviorally understand how to navigate their way toward Mexico. — javra

The fact that they do it is powerful evidence that they do know what they're doing. Perhaps one day we'll understand how they know the route . But it's not impossible that we might come to the conclusion that the butterfly doesn't "really" understand or know what it is doing or why. It's a very limited bit of know-how - not the same as understanding how to navigate the world. Compare migrating wildfowl which are rather less limited and more flexible.

[JTB type of] Knowledge is always in terms of concepts and can be passed on by means of words or other symbols. Understanding is not conceptual, and therefore cannot be passed on. It is an immediate experience, and immediate experience can only be talked about (very inadequately), never shared. — https://www.anthologialitt.com/post/aldous-huxley

It depends what you mean by "shared". We can both understand how to drive a car, even though I cannot understand on your behalf, nor you on mine. It's a bit like eating in that respect.

I’m very curious to see if anyone can discern any other species of knowledge via the way “to know” is used within language that would not fit into any of the three categories just mentioned. (I haven’t yet found any.) — javra

I don't see any reason to suppose that list is complete. But much depends how you distinguish a species of knowledge from knowledge of different kinds of subject-matter.

JTB is fits into many different language-games, and the definition is based on Wittgenstein's family resemblance idea. — Sam26

You are right about that. Partly, the flexibility is the result of the flexibility of justification which is "played" in different ways in different language-games - just as winning is differently defined in different games. But I think it is most at home in the context of "know that.."

To be persuaded is no guarantee of the soundness of what has done the persuading. I just don't see how the truths or falsities that constitute a purported justification for some belief can be irrelevant. You yourself say that a "false justification is something that purports to be persuasive but is not", which seems to agree with what I just said. Although the "purports to be persuasive" seems wrong, inapt since people are often persuaded by falsities. I would change the "persuasive" there to 'true'. — Janus

You are fixing on "persuasive" too much, and also ignoring the difference between soundness and truth that I have pointed out to you on many occasions.

Your objection is something like, "But justifications don't always objectively justify;" or, "But justifications are not always sound." And again, this involves an equivocation between two different kinds of justification (material vs. formal or subjective vs. objective). The claim, "But justifications are not always true," just muddies up the difference between justification and truth. Justification has to do with soundness or validity, and truth is different from justification. Particular truths cannot be known apart from mental acts and justification/explanation, but the concept of truth remains different from the concept of justification.

One could perhaps dispute the idea that justification and truth should ever be separated, even conceptually, but that is a very unorthodox idea which would involve one in an extreme form of internalism. Given the nature and limits of human memory it simply isn't plausible.

We don’t need epistemology to know; epistemology is an after-the-fact rationalization of what life already does. Epistemology is like a priest arriving after the festival, declaring rules for the dancing that already happened. — DifferentiatingEgg

OK, I can see how some out there want to pigeonhole everything into their own devised conceptual containers (i.e., schemas). For one among many examples: everything is physical (this being the devised conceptual container) so therefore all thoughts, intentions, passions, etc., too must be and thereby are purely physical. Yet there are also those whose main intent is to seek understanding via their studies and inquiries, such that first there is X and then there is understanding of what X is. Here, then, epistemology is simply the striving of greater understanding regarding an X that already is, an X taking the form of the epistemic, and this via its study. To better understand the ready-existent regulations by which something operates is not the same as pigeonholing everything into rules of one’s own creation.

Yes, this presupposes a great value to understanding. But that’s maybe a different topic.

[JTB type of] Knowledge is always in terms of concepts and can be passed on by means of words or other symbols. Understanding is not conceptual, and therefore cannot be passed on. It is an immediate experience, and immediate experience can only be talked about (very inadequately), never shared. — https://www.anthologialitt.com/post/aldous-huxley

It depends what you mean by "shared". We can both understand how to drive a car, even though I cannot understand on your behalf, nor you on mine. It's a bit like eating in that respect. — Ludwig V

To better illustrate A. Huxley’s views via a more extreme example: a mystic’s understanding of reality at large (which can be presumed gained via some form of, say, ecstatic experience or some such) cannot be shared in the complete absence of JTB knowledge regarding this understanding, via which the understanding could then be convincingly communicated to others. Notwithstanding, the given understanding nevertheless occurs, as then does the respective knowns-via-understanding regarding reality at large. As to possible examples of this, both Jesus Christ and the Buddha could be deemed to have been in possession of some such understanding which they did their best to impart, to not here get into William Blake and many another. More mundanely, though, most understandings among adult humans in a society are commonly held by all individuals (e.g., the understanding of which side of the road to drive on). But consider how kids learn language: they must come to their own understanding regarding what words in their proper contexts signify. One cannot impart this understanding to children directly (in contrast to how a JTB can be directly imparted among adults), but can only lead the way toward it via affirmations and negations regarding what is correct. This until the understanding clicks.

I don't see any reason to suppose that list is complete. But much depends how you distinguish a species of knowledge from knowledge of different kinds of subject-matter. — Ludwig V

Right. Never say never. Which is why I’m asking a broad community for examples that exemplify knows which are neither JTB, nor understanding, nor awareness (and the acquaintance it entails).

As to distinguishing species of knowledge from knowledge of different kinds of subject-matter:

Awareness of does not require either understanding or belief. So knowledge by acquaintance is distinct from the other two as a species of knowledge.

Understanding does not require belief of what is understood, and, though it does require awareness, it is additional to pure knowledge by acquaintance. So knowledge by understanding is also a distinct species of knowledge.

JTB, on the other hand, will require a) belief (that is both true and endlessly justifiable in valid manners in principle), b) some measure of understanding, and c) awareness. So it too is distinct from the other two.

That briefly addressed, each of the three types of knowledge can apply to vastly different kinds of subject-matter.