I think it is the case that we don't know anything for certain. But if that is the case, how can we know that we don't know anything for certain? This is related to Socrates's famous remark that all he knows is that he knows nothing for certain. But maybe we can't even know if we know nothing.

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    We don't know that "for certain" either, but we are pretty sure. As with everything else, "knowing for certain" is a useless expression when taken literally. Only omniscient God knows anything "for certain".
    – Conifold
    Commented Oct 31, 2023 at 20:23
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    What if we just quasi-know, for certain, that we don't know, for certain? And you might ask, "How do we know that we quasi-know?" but then we could reply, "Ah, but we don't, we quasi-know that we quasi-know," and proceed apace. Commented Oct 31, 2023 at 23:10
  • If I remember Sextus Empiricus correctly in Pyrrhonian Skepticism we do not claim to know this but we have observed that we can always produce isosthenia (two opposing arguments of the same strength) and we will do so if we ever have to counter our belief in certainty
    – dlrlc
    Commented Nov 1, 2023 at 13:24
  • If you are imagining that there is some sort of distinction between "knowing" and "knowing for certain" (this seems to be strongly suggested by the way you phrase your question), then there is no contradiction in saying "I know that I don't know anything for certain". There would only be a contradiction in saying "I know for certain that I don't know anything for certain".
    – Pilcrow
    Commented Nov 1, 2023 at 15:04
  • @Conifold: You're too pessimistic. Can't you know for certain whether you exist? I mean, what's the point of your comment, if not?
    – Marxos
    Commented Nov 2, 2023 at 21:35

2 Answers 2


I think part of this is what we mean by know. If we take knowledge as justified true belief (i.e., must be the result of true premises and an inference method), then you need to be rational to know anything; this rules out most, if not all other species from knowing anything.

However, I'll take the foundationalist view that there are some unjustifiable true facts upon which we can reason from.

Specifically, we know one at least one thing for certain - we are (ala Descartes). It is a brute fact that is immediately known and irrefutable. You cannot be fooled into thinking you exist, nor can we say it is an illusion, if only because an illusion (or any experience) needs a subject and therefore if there is an experience there is the subject having that experience, by necessity.

This is well summarized by James Pryor in “There is Immediate Justification”, in Turri, Steup, & Sosa (eds.) Contemporary Debates in Epistemology. 2nd Edition, Blackwell (2013)

I believe that I feel tired, that I have a headache, that I intend to get a glass of water, that black is not white; and in each case, it doesn’t seem that my justification is mediated by any other proposition. This supports the claim that there are foundational beliefs, though it does not speak directly to the thesis that all other beliefs must depend, ultimately, on foundational beliefs for their justification.

(Source: Hasan, Ali and Richard Fumerton, "Foundationalist Theories of Epistemic Justification", The Stanford Encyclopedia of Philosophy (Fall 2022 Edition), Edward N. Zalta & Uri Nodelman (eds.), URL = https://plato.stanford.edu/archives/fall2022/entries/justep-foundational/)

People confuse this basic fact with more nuanced positions that make claims beyond the necessary experience-experiencer pairing, which is where we get into Reliabilism, content externalism, etc which move from just "I am a subject" to trying to interpret the world beyond our minds.

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    I’m a bit sceptical that the “cogito” is a tough argument in the light of current philosophy of mind taking into account also neuroscience. Because even introspection leads only to the content of our self-model. The latter is a brain construct as the result of much internal processing. Its function is to provide an aggregated and consistent view of all stimuli and perceptions. The self-model is embedded into the world-model. (1/2)
    – Jo Wehler
    Commented Nov 1, 2023 at 7:32
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    We know from mental disturbances that both models may have faults – an analogue of the malevolent demon of Descartes, but in the absence of God. - The self-model theory is due to Th. Metzinger and is under discussion like the Integrated Information Theory is. One key feature: Both models are transparent. But we cannot experience that they are models while pretending direct access to the world. (2/2)
    – Jo Wehler
    Commented Nov 1, 2023 at 7:32
  • @JoWehler can you dumb down you comments for me ;-) I'm having a hard time grasping what you are getting at. I am not arguing for the reality of an eternal self or homunculus, if that is what you are getting at. A subjective experience is, necessarily, aware of itself, right? That awareness is direct, unmediated knowledge of having that experience. I'm not saying that knowledge tells us anything further (e.g., we have a soul, there is an outside world that looks like it appears to me). What I was getting at above is we are certain of the contents of our self-model.
    – Annika
    Commented Nov 1, 2023 at 12:38
  • Sorry for being unclear. – I agree with the first part of your comment, up to the question mark. – I am sceptical about the attribute “direct” in the second part. My point is that even our self-model can fail. Each software has faults, also the self-model may have faults or may become faulty. Then our self-model fools us, producing mental disturbances up to ego disorder and several forms of psychosis. - Concerning the self-model theory see "Thomas Metzinger: Being No One". For me it is a very challenging book, even when reading his many popularizations first. It is a heavyweight like IIT.
    – Jo Wehler
    Commented Nov 1, 2023 at 15:37
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    "What is the thing that it is failing to do?" The self-model of a person with a mental disorder fails to process the input stimuli in a way which allows the person to orientate oneself and to act like nearly all other humans do in the same environment. (I do not touch on the problem how to define a norm.) – Please let me know if I misunderstood your question.
    – Jo Wehler
    Commented Nov 1, 2023 at 16:44

If I remember right, Socrates did not say "I know that I know nothing", but "I do not believe to know what I do not know (Apology 21 d7 )".

I understand the latter statement as follows: I know that also I myself do not know the answer to the far reaching questions which I ask to the experts. The experts, who being experts on their field, believe to know also the right answers on many more other fields.

  • "I seem, then, in just this little thing to be wiser than this man at any rate, that what I do not know I do not think I know either." -Socrates, in Plato's 'Apology'
    – CriglCragl
    Commented Oct 31, 2023 at 23:20

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