"Skepticism, while logically impeccable, is psychologically impossible, and there is an element of frivolous insincerity in any philosophy which pretends to accept it. Moreover, if skepticism is to be theoretically defensible, it must reject all inferences from what is experienced; a partial skepticism... has no logical justification, since it must admit principles of inference which lead to beliefs that it rejects." Russell, Human Knowledge.

Why is skepticism psychologically impossible? I am presuming he means that one cannot go about the world being a skeptic. But this presumes that actions require knowledge (if defined in a complete sense) which is at the very least a controversial position.

One can acknowledge that justification for a belief cannot be possible without having faith in certain axioms (such as the world being real) and yet still do things based on that faith. Where is the “impossibility” here? I’d argue we do this all the time.

  • It seems the great Bertrand Russell, like his fanatical protégé Ludwig Wittgenstein, had an early and late phase.
    – Hudjefa
    Sep 7, 2023 at 2:42
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    – Philip Klöcking
    Sep 7, 2023 at 4:31
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    The question is unanswerable without the context that explains what Russell meant by "skepticism". AFAICS only Descartes style radical skepticism is psychologically impossible, whereas e.g. scientific skepticism is a learned skill, has no implications of perfection or total absence of cognitive biase, and is best (IMHO) implemented as a deliberate choice. Sep 7, 2023 at 12:05
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    @DikranMarsupial - a good context (maybe not the same source...) is B.Russell, Human Knowledge Its scope & limits (1923), Part III, Ch.II Solipsism, page 191-on: "We may distinguish two kinds of solipsism, which I shall call "dogmatic" and "sceptical" respectively." Sep 7, 2023 at 12:54
  • @MauroALLEGRANZA I did a bit of looking around and I think he may have been talking about Descartes type of skepticism specifically, in which case my response is "well, duh!" (I think Descartes may have agreed). Sep 7, 2023 at 14:43

6 Answers 6


Consider Buridan's Ass -- the story of the perfectly logical donkey standing between two equal sized bales of hay. The donkey has no reason to choose one bale over the other and hence it starves.

Now consider the perfectly skeptical llama in the adjacent field. The llama stands in front of a single bale of hay. Unfortunately for it, the llama is perfectly skeptical. Due to its skepticism, the llama has no reason to believe the bale of hay is there. It also has no reason to believe the bale of hay is not there.

In both cases you have an animal that must ditch its philosophy in order to justify any action.

But the llama is in an even bigger pickle than the donkey. For the llama must ditch its philosophy in order to justify any inaction.

Bad news for Mr Llama.

  • that's really good! playful and to the point
    – Deipatrous
    Sep 7, 2023 at 13:07
  • I love this answer but I think if you are not familiar with ''Buridan's ass" (I didn't name it!) you might not understand that there's a very specific idea of 'logical' required. In other words, I think the idea that starving while looking at two perfectly good piles of food is 'logical' might be a little confusing to many people.
    – JimmyJames
    Sep 7, 2023 at 21:30

We're all extremely far from our impoverished state of birth, riddled with knowledge and justification. The brain learns how to operate its own body early on. We'd have no concept for skepticism before acquiring vast amounts of knowledge. We can turn to Chomsky at this initial stage, he says few triggers early on in our development unlock exponentially more knowledge, justification, belief, etc, as some of this capacity is innate waiting to be triggered. Another strong quote from neuroscience is "the first thing the brain knows is the body", by Dean Buonomano. Skepticism is thus always retroactive, and instinct is always contaminated with it.

You'd have to learn how to block it all out after the fact, but how could a skeptic do that? Unlearn by learning how to pare it all down, and then become a skeptic at the end? Sounds like the opposite of psychologically tenable. Sounds like denial and suppression.

I don't think this is quite Russell's data in support of his argument, but it's not too far off, and uses recent ideas like Chomsky's and neuroscience. This is for strong skepticism, and we do not do this all the time. What do we call a toddler who refuses to learn? Stubborn. Not skeptical.


'Skeptic' in the stronger sense means disbelief in knowledge. So, to make the claim that there is only belief and nothing is justified, true, or certain is actually a rather radical claim. Intuitively, most thinkers understand that there are certain beliefs that are reliable. I see the floor in front of me, and I needn't worry about dropping into a pit. I feel hungry, I believe I'm hungry, then I know I'm hungry. Why would anyone doubt that? It would take an exceptional person to engage in such systematic doubt. In fact, Rene Descartes is famous for introducing that doubt as a flavor of foundationalism.

Overcoming the Skeptic Problem can be seen an excellent epistemological exercise because most people have such a strong intuition that one knows and does not merely believe that it's rather difficult to convince people to be skeptical about what they are habitually attuned to (as per Hume's psychological explanation for using induction). Some might even say that radical skepticism is self-refuting. Consider that to "claim strongly" that nothing can be known begs itself a justification, and any attempt to justify the claim instantly carries with assertoric force. Almost by definition, certainly by psychology, claims of fact are claims of knowledge.

Is it possible for people to think and conduct discourse without fact? It seems hard to imagine how. It would be so unnatural to have an ontology and modality presumed in one's speech as to require constant caveat's?

Today is Friday, though I might be wrong. Friday's are my favorite days, I think but might reconsider. My friend will meet tonight, though I'm not sure why I trust his testimony. We're going out for a beer, presuming beer exists.

That's just unnatural.

  • if some things are true but we don't know them only believe them true, then a lot of discussion is useless, for sure. what is happening when we try to justify things to others?
    – user67675
    Sep 6, 2023 at 23:07
  • All of this hinges upon the assumption that we need justifications to act. We don’t. We merely need instinct. Everything is a gamble. Gambles that “seem” more reasonable aren’t actually that. What seems more reasonable is itself another gamble, an instinct of sorts. Everything is instinct.
    – user62907
    Sep 6, 2023 at 23:36
  • @prof_post We are attempting to persuade them by getting them to agree on outcomes.
    – J D
    Sep 7, 2023 at 13:23
  • @thinkingman It would be a very clever response except for the fact that you obviously felt the need to provide a justification in your response. Clearly among our instincts is the instinct to justify.
    – J D
    Sep 7, 2023 at 13:27

I assume you mean to ask does anyone really believe it?

Like he points out, it is logically consistent to think that nothing can be justified except that nothing can be justified (this isn't self refuting, just poorly worded by me). At times, people don't attempt to justify any beliefs, only use instinct to act, don't reason about anything. Does that mean they never do?

If you have beliefs, you would be hard pressed to convince me that you cannot justify any of them and that doesn't matter to you, let alone anyone else. The belief the GPS is working, tacit or not, would amount to something different if you couldn't justify it, tacitly or not. You'd check it more, anyway. You might reply that you instinctively suspect that it's stopped working, cannot justify the claim that you are going the right way, but

some people class reliable processes as justifying ones

A functioning GPS is reliable, so why doesn't it justify - to you or objectively - your belief in your location?

Two quick examples - everyone has had knowledge, and without it our beliefs are unreliable - of reasons to think that it is psychologically implausible to claim you cannot justify anything. It may not be certainly so, but then philosophy rarely deals in certainty.


I was taken to task recently for saying that there are definitely no aliens visiting the Earth, because I could not rule out the 1% chance that they are. (A reasonable estimate of that probability would be more like 1 in 10^100, but my interlocutor was the sort of person who might think that 1% is the smallest sort of chance you can get.)

And we encounter this attitude from time to time: they retract to the austere position that nothing (but nothing!) can be known with full certainty. True enough. But in practice we treat something as (as good as) certain when the odds of it not being so fall below an agreed-upon tolerance level.

(What sets that level is a whole field of study in its own right, but we will leave that aside.)

Russell is commenting here on that stance. The heroic skepticism of one "who doubts everything" could not possibly be sustainable for more than a moment in real life (both for psychological reasons and others) and in practice we have to deal with the much tougher question of where we draw the lines.

  • One who doubts everything is a practical position. One who disbelieves everything is an impractical one - some things must be true or the whole system fails.
    – Suncat2000
    Sep 8, 2023 at 23:27

Skepticism is a belief that nothing can be known with absolute certainty. If one accepts that definition, then skepticism being logically impossible that is logically impossible, so I disagree with Russell. It also depends on the amount of uncertainty one is willing to accept.

For example, the air I breathe is one of the things that is keeping me alive. I am skeptical that the air is completely pure and it may in fact be harming me. However, since I am still breathing and still alive, I plan to keep doing it, regardless that I am not 100% certain that breathing the air won't kill me.

We may accept patterns that the universe behaves in certain ways but it only takes one instance of contradiction to prove that absolute certainty does not exist. Skepticism is simply doubting that everything is perfect.

I posit that lack of skepticism is psychologically impossible. With our imperfect knowledge, skepticism is psychologically necessary in order to adapt our activities to compensate for the knowledge we lack. But I'm not perfectly certain of that.

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