If it's true, then do I already know that it's true?

And, if I know that I know something, then do I know it? I'm not sure I know what knowing that I know could mean, beside an expression of not knowing something until reflecting on e.g. its coherence with other beliefs.

I hope that makes sense / is cogent...

  • youtube.com/watch?v=4SQpczc8mGg Commented Jun 14, 2014 at 9:49
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    Its an axiom that is part of epistemic logic; it only makes sense really if you are studying it; Commented Jun 14, 2014 at 11:18
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    that's a strange comment to make - really it can't be understood without vast amounts of logic?
    – user6917
    Commented Jun 15, 2014 at 16:23

1 Answer 1


The KK principle doesn't imply that everything that is true is already known. That's a very different claim. There are people who endorse it--Kant does, for instance. But many contemporary philosophers would take this to lead to some kind of pernicious idealism.

What the KK principle says is that everything you know, you know that you know. If I know paris is the capital of france, then I know that I know that paris is the capital of france. In other words, knowledge is transparent. It is impossible for me to have some knowledge which I am unaware of.

The reason to hold some thesis like this is a claim about the nature of knowledge. If you think to have knowledge is to have some evidence, or something like that, then you'd be attracted to the principle.

On the other hand, if you think that knowledge can be produced by reliable belief forming processes or something that operate whether you are conscious of them or not, then you'd want to deny the principle.

it is clear that you can fashion consistent epistemic logics either with or without the KK principle, so the question whether the KK principle is true or not isn't a logical, but a philosophical question.

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    Oh, for more on the claim that everything true is known, see The Fitch Paradox, sometimes also called the paradox of knowability. There's a great article in the Stanford Encyclopedia on it.
    – user5172
    Commented Jun 14, 2014 at 13:37
  • Shane left very little to add. Two minor notes: (1) From the epistemic logical point of view, accepting or denying the KK means accepting or denying the transitivity of the epistemic accessibility relation; (2) There is an ever stronger principle, which we could call 'NKKNK', which says that if you don't know something (¬Kφ) then you know that that's the case (K¬Kφ). This also rejected principle corresponds to the assumption that the epistemic accessibility relation is euclidean. Commented Jun 14, 2014 at 15:39

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