A recent question about the Plato's formula K=JTB (knowledge is justified true belief) made me curious as to what Kant thought on the matter. In the prefaces and the Introduction to the first Critique knowledge is mentioned in every other paragraph, but surprisingly Kant never spells out what he means by it, or mentions JTB. He distinguishes empirical and a priori knowledge, and even pure and impure a priori knowledge. He is very pragmatic on empirical knowledge saying that "empirical judgement never exhibits strict and absolute, but only assumed and comparative universality (by induction); therefore, the most we can say is — so far as we have hitherto observed, there is no exception to this or that rule".

In principle, Kant's usage can perhaps be subsumed under JTB, but it seems equally consistent with "knowledge first", where it is an irreducible notion taken for granted. While JTB may sit well with his pure a priori knowledge, his empirical knowledge might better fit into modern pragmatic theories. This pragmatism and sharp separation between knowledge and belief ("I had to limit knowledge to make room for faith") make me skeptical that Kant is operating under JTB. Weyl, with his strong Kantian leanings, also explicitly contrasts knowledge and belief. Plato is mentioned in the Introduction only to be mocked:"Plato, abandoning the world of sense because of the narrow limits it sets to the understanding, venture upon the wings of ideas beyond it, into the void space of pure intellect. He did not reflect that he made no real progress by all his efforts; for he met with no resistance which might serve him for a support...".

Did Kant state his position on knowledge and its relation to JTB definitively somewhere? What does modern scholarship make of his uses of "knowledge"? Did he inspire some modern alternatives to JTB?

2 Answers 2


Key text here may be On opinion, knowledge and belief, CPR B 848-859.

There is conviction [Überzeugung]. It is the subjective part necessary for knowledge:

Taking something to be true is an occurrence in our understanding that may rest on objective grounds, but that also requires subjective causes in the mind of him who judges. If it is valid for everyone merely as long as he has reason, then its ground is objectively sufficient, and in that case taking something to be true is called conviction. (B848)

The "objective" aspect of knowledge is "certainty" [Gewissheit], and only if both occur together, this can be called knowledge. Kant speaks of three possible variations in respect to conviction:

Taking something to be true, or the subjective validity of judgment, has the following three stages in relation to conviction (which at the same time is valid objectively): having an opinion, believing, and knowing. Having an opinion is taking something to be true with the consciousness that it is subjectively as well as objectively insuffıcient. If taking something to be true is only subjectively sufficient and is at the same time held to be objectively insufficient, then it is called believing. Finally, when taking something to be true is both subjectively and ob- jectively sufficient it is called knowing. Subjective sufficiency is called conviction (for myself), objective sufficiency, certainty (for everyone). (B850)

To paraphase:

Opinion: We are neither convinced regarding the objectivity of the proposition because of a valid judgement nor certain that this judgement will be the same for every rational being.

Belief: We are convinced that it is true because it is the result of valid reasoning based of our personal experience ("subjective causes in the mind of him who judges"), but not certain that it is the same for every rational being.

Knowledge: We are convinced that it is true because it is the result of valid reasoning based on our personal experience ("subjective causes in the mind of him who judges"), and certain that it is the same for every rational being (because even if it is based on personal experience (empirical), it is - itself - not reliant on that particular experience).

It is different from JTB in that beliefs - taken this to be true - are always justified. Also, "truth" cannot be empirical truth, but has to be a priori, as only there, certainty is to be found.

To further bolster my assessment as being backed by Kant's own words:

l must never undertake to have an opinion without at least knowing something by means of which the in itself merely problematic judgment acquires a connection with truth which, although it is not complete, is nevertheless more than an arbitrary invention. Furthermore, the law of such a connection must be certain. For if in regard to this too I have nothing but opinion, then it is all only a game of imagination without the least relation to truth. In judging from pure reason, to have an opinion is not allowed at all. For since it will not be supported on grounds of experience, but everything that is necessary should be cognized a priori, the principle of connection requires universality and necessity, thus complete certainty, otherwise no guidance to the truth is forthcoming at all. (B850-51)

One aspect is that of "problematical" judgements, which could be understood as "may be"-judgements (see e.g. GMM, 4:414-5). The other one is that he seems to claim here that all knowledge (other than a priori principles themselves) has to be derived from a priori principles, which, albeit "resting on empirical grounds", remain a priori (see Prol., Ak. 4:373-4,fn.). This is closely linked to Kant's understanding of science, which I have elaborated in the context of this answer.

On truth, a priori, and certainty

The status of a priori knowledge is questionable and I am sympathetic with a reading originally worked out by Onora O'Neill ('89, '90, '92) and summarised by Pawel Lukow (Kant-Studien 84:2, 204-221, pp. 205-6) as follows:

According to a constructivist reading of Kant's approach, philosophy uses and can only use a negative procedure: it rejects all claims that do not survive self- criticism, and all claims that cannot be followed by all. Even the process of vindicating reason uses, and can only use, these two strategies. On the one hand we reject principles which, as far as we can determine, are self-defeating, and, on the other hand, we reject principles that not all can follow. In consequence, we provisionally retain only principles which do not contradict themselves and which we hold that all can follow. By these procedures, we arrive at an account of certain principles — which we come to view as those of reason — which resist refutation when subjected to reflexive self-criticism. This is not to say that these principles are the right ones, judged by some transcendent conception of reason, or that these are all the unrestricted legitimate principles there are. The principles that survive testing are still open to criticism. Vindication of reason is viewed as an incompletable task, standards of reasoning are provisional: construction is a matter of (negatively) rejecting some provisional proposals and retaining others rather than that of (positively) proving determinate proposals.

This view of vindication is exemplified by Kant's specifically juridical6 under- standing of 'deduction'. He makes a trial (or experiment; Versuch] where main procedure is negative. A 'deduction' is not a logical proof but legitimization (Rechtfertigung-, cf. for example Kr.d.p. V., 45).

Thus, arguably, a "deduction" (juridical sense) that shows that a proposition is not self-contradictory and can be followed by all is what makes a belief justified in the sense of certain beyond a reasonable (rational!) doubt. Mind, for Kant reason works on the basis of experience (Prolegomena, 4:373 fn.) and pure speculation is irrational and has to be vindicated by critical reason. In other words: Radical scepticism with Cartesian spectres like Brains-in-a-vat is irrational as in "purely speculative".

Also, there is no differentiation between true and justified because there would have to be an independent, justifiable, true criterion for truth leading to an infinite regress or scepticism.

Since the Kantian conception of knowledge is supposed to defeat sceptical objection above all else, it seems fitting that Lukow concludes:

Although the authority of reason cannot be proved in this way, it has at least survived refutation. (207)


Altogether there are some similarities, but I would say the Kantian concept of knowledge is much more restrictive since his understanding of truth forbids knowledge being empirical - following Hume's philosophy but going beyond.

The main difference is that there is no differentiation between true and justified since the justification is what determines the truth.

Edit as I stumbled across it:

In his Metaphysical Foundations of Natural Sciences Kant restates this strict sense of knowledge, saying that knowledge [Wissen] that is founded in empirical findings is not to be called knowledge [Wissen] in a strict sense (Ak. 4:468). He distinguishes once more between knowledge [Erkenntnis], that is apodictically certain and systematically gained by principles a priori, and experience [Erfahrung] that is founded by empirical facts and/or gained through empirical principles.

What is therefore needed for knowledge is the "construction of the concept" (any Hegelians knowing this? now you know how strong Kant's influence was!) through schematism, i.e. especially pointing out the connection between a priori and intuition in order to prove the objective reality of the concept. Förster describes this in his chapter on the Foundations, reflecting on the preface.

  • Ah, I forgot about that section. "Problematical" judgements seem to refer to empirical ones, where Kant allows for opinion, but only on condition that their connection to the truth, if not their content, is a priori grounded. Then it would seem that he allows for less than truth in "empirical knowledge". It is also interesting that he treats knowledge and belief disjointly, on his meaning knowledge is not a particular case of belief b/c belief "is recognized as being objectively insufficient". This is how intuitionists interpret it too, so I guess Kant is the source.
    – Conifold
    Commented Jan 4, 2016 at 21:19
  • @Conifold: Regarding intiutionists, I'd rather say that Fichte and Hegel are the source on that one, because they are strongly influenced by and using kantian terminology, but are trying to enable pure intuition as a possible "direct" way to knowledge for human beings.
    – Philip Klöcking
    Commented Feb 16, 2016 at 18:47
  • 1
    Off topic perhaps, but it is, to put it mildly, 'controversial' that JTB is Plato's formula.
    – sand1
    Commented Feb 17, 2016 at 9:40
  • @sand1 - My thought also.
    – user20253
    Commented Jan 21, 2019 at 14:44

To understand Kant's concept of knowledge, it is necessary to note that

(1) for him, knowlege is not first a relation between a subject and a proposition but a relation between a subject ( the knower) and an object ( a thing).

(2) according to him, knowledge as knowledge-that ( as relation to a proposition) is a component of knowledge as knowledge of a thing, or of an object: it is through knowledge-that that knowledge-of comes to it's accomplishment.

What shows that knowledge-of is more fundamental to Kant than knowledge-that is that kant attemps to provide a transcendental logic: before determining whether our judgments are true or false ( before determining whether they qualify as knowledge-that) it is necessary to explain the possibility of the relation existing between subject and object, that is it is necessary to explain knowledge-of.

Knowledge as knowledge-that is defined in the Logic, and also in the part of the Critique of pure reason called Methodology, where Kant distinguishes 3 kinds of " assent", 3 ways to " hold as true" a proposition ( the content of a judgment).

Knowledge as knowledge-of is analysed in the beginning of the Transcendental Aesthetics in the Critique of pure reason. For the human subject to have knowledge of something, 2 conditions must be met :

(1) first, the object has to be given, and this givenness of objects implies sensibility, sensible intuition ( which distinguishes a finite being's knowledge which requires receptivity, and an infinite's being knowledge that is productive, that produces objects by the same act as it knows them)

(2) second the object has to be thought, recognized as object, by means of a judgment that subsumes the object under the concept ( hence the necessity of categories, a priori concepts of an object in general).

So knowledge-of , in the case of human beings, is according to Kant an organised and stuctured combination of intuitions and of concepts. To know an object is to (1) determine through concepts and judgments an object that must be (2) given.

No knowledge without this combination : " intuitions without concepts are blind ; concepts without intuitions are empty."

  • 1
    Hey, thanks for taking the time to compose this answer. Maybe it could be improved by a) bolstering the overall correct assessments with references or quotes that link them to specific passages of Kant's writings, e.g. for the need to have the object as given vs. infinite mind CoJ §77, and b) adding something about the in fact problematic tension between the criterion of certainty which Kant ascribes to knowledge and the empirical knowledge not being "certain" in the same sense as knowledge a priori.
    – Philip Klöcking
    Commented Apr 1, 2019 at 8:41

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