On Wikipedia, knowledge is defined as justified true belief:

The concept of justified true belief states that in order to know that a given proposition is true, one must not only believe the relevant true proposition, but also have justification for doing so. In more formal terms, an agent S knows that a proposition P is true if and only if:

  • P is true
  • S believes that P is true, and
  • S is justified in believing that P is true

So can we really know something if we cannot know whether it is true? For example, if I know dinosaurs did exist once, then:

  • Dinosaurs did exist once
  • I believe dinosaurs did exist once
  • I'm justified in believing that dinosaurs did exist once

The last two are satisfied: I do believe dinosaurs did exist once, and I'm justified in believing that, by what I know through biology and archaeology (ancient, large bones that match the shapes of giant weird animals). It is very strong evidence, but I still not know whether or not dinosaurs did exist once.

Now, I know not all truths are established truths. From The Analysis of Knowledge (Stanford Encyclopedia of Philosophy):

Something’s truth does not require that anyone can know or prove that it is true. Not all truths are established truths. If you flip a coin and never check how it landed, it may be true that it landed heads, even if nobody has any way to tell. Truth is a metaphysical, as opposed to epistemological, notion: truth is a matter of how things are, not how they can be shown to be.

So it seems that for anything that we cannot directly check its truth but only infer it, we can only have justified belief on it. But then, the statement "Dinosaurs did exist once" is commonly regarded as "knowledge". So is this statement actual knowledge, or is it just justified belief?

  • 1
    Why "do you not know whether dinosaurs did exist once" ? Feb 27, 2020 at 12:08
  • Asserting P is the same that saying "P is true". Are you asserting "Dinosaurs did exist once" ? Feb 27, 2020 at 12:09
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    Maybe useful Knowledge as Justified True Belief: The Truth Condition: "Most epistemologists have found it overwhelmingly plausible that what is false cannot be known. One can only know things that are true." Feb 27, 2020 at 13:08
  • The wikipedia page doesn't say "Knowledge is defined as justified true belief". Don't misrepresent your sources.
    – E...
    Feb 27, 2020 at 13:19
  • @Eliran sorry, the quote was not exact. At first I was try to write it on my own, then later decided that I should quote it. But I didn't delete my version. Anyway, it does say "Justified true belief is a definition of knowledge". It doesn't much affect my question I suppose
    – Ooker
    Feb 27, 2020 at 13:46

2 Answers 2


Justified True Belief as a criteria for knowledge sets two conditions which are not satisfiable for the vast majority of what we know. Empiricism operates off an indirect realism assumption, in which we can arrive at most likely working hypotheses about reality, but can never have certainty for any of them. This means we do not have access to "truth" for empirical questions. IE nothing we learn from science or any other empirical process can satisfy the "true" criteria of Justified True Belief.

Additionally, the Munchausen Trilemma points out that all "justifications" must reference an unjustified assumption, be infinite series (and therefore never completed), or be logic loops (and therefore fallacies). IE, none of our knowledge, be it empirical OR rational, satisfies the strong concept of logical "justification" either.

Yet we clearly know things. Pragmatically, the inventory of knowledge we learn from teachers, family, and peers is massively useful in dealing with the world. What we learn is therefore knowledge. The definition you used -- does not accurately delineate what knowledge is.

Most people grow up believing in direct realism, not indirect realism. Your example, dinosaurs, is designed to short circuit anyone who tries to assert direct realism provides access to truth, and therefore evade one aspect of the problem, as the existence of dinosaurs is only inferred indirectly.

One solution is to accept that knowledge does not require either "truth", or a strong logically fully consistent "justification", but is a pragmatic term, for things we can think we know with a high degree of certainty. The problems with knowledge is one reason why science is predominantly a pragmatic field, not a logic-focused one.

To answer your question, scientists and most people use a pragmatic definition of knowledge, without demanding truth, or full logical "justification", but instead good supporting rationale. Yes, for those who treat concepts and knowledge pragmatically, one can know that dinosaurs did exist once.

This pragmatic knowledge IS "justified belief", with a weak meaning of "justified" where it is "well supported" not logically established.

  • "This pragmatic knowledge IS "justified belief", with a weak meaning of "justified" where it is "well supported" not logically established." Why do you speak of "logically established": no empirical knowledge can be "established" with logic alone. Facts are known through experience (direct and indirect) and this is exactly the way we (humans) have used to know about the existence of dinosaurs (and quarks). Feb 28, 2020 at 9:37
  • @MauroALLEGRANZA - The Munchausen Trilemma shows that all rationales depend on unjustified assumptions, or a logical fallacy. Empirical science depends on the empirical process. Empiricism is itself justified by its pragmatic effectiveness, which IS an empirical justification IE a self-referential logic loop. Empirical knowledge does not satisfy the logic category of "justified", just as it does not satisfy "true". Yet it IS knowledge, hence knowledge does not need to satisfy JTB.
    – Dcleve
    Feb 28, 2020 at 15:08

I think it is important to make a distinction — with the caveat that few people make this distinction, to everyone's detriment — between the politics of knowledge and the pragmatics of knowledge. Pragmatically, when we say we know something (following Wittgenstein), what we mean is that we have recognized a pattern in the world and can make fruitful hypotheses about it. What we know is a model of the world, and that model can be revised and elaborated in ways that make it more useful or functional. In that sense our model might tangentially approach a 'true' description of the world-as-it-is, but we never know the world-as-it-is in any meaningful sense.

Politically, however, every knowledge claim is also a power claim. We want to say "Dinosaurs existed" in that flat, declarative tone, not "The observations I have amassed lead me to a model of the world in which dinosaurs once existed." The latter statement sounds as though one is merely offering an opinion, not presenting a functional truth based on evidence, reasoning, and hard research. Lots of less than savory people are willing to use that apparent 'softness' as an avenue to present off-the-wall theories with questionable power motivations of their own. Anglophone philosophy has fixated on this political aspect because of the peculiarly combative relationship it has with established religious authority, and so a lot of time and effort has gone into the question of how to establish a right to declarative truth of this sort.

It's all pretty much to no avail, of course, but it has made for a lot of interesting philosophical discussions.

In the Justified True Belief system, point 1 ('P is true') is always a matter of metaphysics, and point 3 ('S is justified in believing that P is true') is always treated in an under-theorized and somewhat shallow sense. 'Justification' is not the simple, linear, in-your-face concept in the way it is often presented.

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