I don't really understand why some philosophers claim that it's impossible to be absolutely certain of anything except my own consciousness. Isn't that absurd? Personally I believe that this kind of extreme skepticism is just wrong and that it's possible to obtain 100% certainty. I believe that we're just looking at what we don't know in the wrong way. The best argument I have heard so far is: we can't be 100% certain of anything because we don't know everything. I mean, I don't know why I perceive colors, does that mean I can't be 100% certain I perceive them. What do you think?

  • It's depressing not to know with ABSOLUTE certainty that climate change even exists within reality in the first place. Do you understand what I am saying? Honestly I don't believe this kind of nonsense philosophy, to me extreme skepticism is as wrong as no skepticism, but I would like to understand why so many people actually agree.
    – user34482
    Aug 6, 2018 at 17:17
  • Yes, I know what you're saying. And people should indeed be very careful not to draw the wrong conclusion from this kind of extreme skepticism: when applied to climate change, it would indeed be all too easy for someone to say: "well, but we're not 100% certain it's there, so why should I care" ... and the obvious problem is that while 99.999999999% certainty is not 100% certainty, that's no reason to basically say "whatever". It's the same mistake people make when they dismiss something like the theory of evolution with a simple "it's just a theory". So yes, I'm with you!
    – Bram28
    Aug 6, 2018 at 17:21
  • Anyway, from your comment I think I didn't quite correctly interpret the point of your post. ... it wasn't so much challenging the truth of the claim, but maybe more the usefulness of it? And the practical usefulness of extreme skepticism? Does that sound about right? If so, maybe you could edit your post and make that more clear? And if so, you also may want to change your title to be more reflective of that.
    – Bram28
    Aug 6, 2018 at 17:24
  • Yes but the idea that the theory of evolution will NEVER reach 100% certainty is just something I can't understand. Correct me if I am wrong but the claim: We cannot know anything with absolute certainty because we don't know everything is preposterous. I can't describe how gravity actually works but I am 100% certain it exists.
    – user34482
    Aug 6, 2018 at 17:28
  • 1
    This reminds me C.S. Peirce:"It is easy to be certain. One only has to be sufficiently vague". "I don't know what gravity is but I know it exists" is already problematic. If "gravity" is meant traditionally then on general relativity it does not exist, it is an illusion created by spacetime curvature. There is an inverse relation between certainty and substance, at 100% certainty we get 100% vacuity like "I am certain that something". The trick is to be certain enough in something substantive enough, 100% is moot.
    – Conifold
    Aug 8, 2018 at 1:50

3 Answers 3


In our philosophy, the sentence, We can't be 100% certain of anything because we don't know everything, is not completely true and needs revision:

We can be 100% certain of the existence of a thing but we cannot be sure of its properties because we don't know everything about that thing.

For example, assume we close our eyes and somebody puts a thing in our hands. We would try to touch it, smell it ... to imagine it with our experience about things. OK! Then we are sure there is a thing in our hands, but what is it? What are its properties? There are maybe many other questions we need answered about it.

There is a very nice poem from molavi in the book, masnavi:

The elephant was in a dark house: some Hindús had brought it for exhibition.
In order to see it, many people were going, every one, into that darkness.
As seeing it with the eye was impossible, (each one) was feeling it in the dark with the palm of his hand.
The hand of one fell on its trunk: he said, “This creature is like a water-pipe.”
The hand of another touched its ear: to him it appeared to be like a fan.
Since another handled its leg, he said, “I found the elephant's shape to be like a pillar.”
Another laid his hand on its back: he said, “Truly, this elephant was like a throne.”
Similarly, whenever any one heard (a description of the elephant), he understood (it only in respect of) the part that he had touched.
On account of the (diverse) place (object) of view, their statements differed: one man entitled it “dál,” another “alif.”
If there had been a candle in each one's hand, the difference would have gone out of their words.
The eye of sense-perception is only like the palm of the hand: the palm hath not power to reach the whole of him (the elephant).
The eye of the Sea is one thing, and the foam another: leave the foam and look with the eye of the Sea.
Day and night (there is) the movement of foam-flecks from the Sea: thou beholdest the foam, but not the Sea. Marvellous!
We are dashing against each other, like boats: our eyes are darkened, though we are in the clear water.
O thou that hast gone to sleep in the body's boat, thou hast seen the water, (but) look on the Water of the water.
The water hath a Water that is driving it; the spirit hath a Spirit that is calling it.

I hope it was useful.

  • I made some edits. You may roll them back or continue editing. You can see the versions by clicking on the "edited" link above. Do you have a reference for the part that you quoted? That would help strengthen your answer. I did not edit that part because I did not know who wrote it. Aug 6, 2018 at 19:55
  • "somebody puts a thing in our hands." - is it possible that there is no thing? That we're getting freaky nerve signals? That we're dreaming? That we're having vivid hallucinations? Aug 6, 2018 at 22:50
  • thanks @frank-hubeny, there are many references in our philosophy like Bu-Ali Sina philosophy or Mulla Sadra's philosophy . Aug 7, 2018 at 0:10
  • @david-thornley, the answer of your question is very long but I tried to give a short answer._beacause the Man is limited in time and place_ could imagine out of them. it means when you are into a room, you could not think and imagine outside the room if you never saw the outside. no thing meant nothing.there are many things we could not touch, like the atmosphere or like mind, but we could have knowledge about them from them's effects.in other words: if we found effects(touchable or not touchable) we would try to find the who is made this effects but if no effects?. Aug 7, 2018 at 0:32

If by 'absurd' you mean 'weird' or 'unexpected', then sure, yes, this is a pretty weird claim: until we encounter these kinds of arguments in a philosophy class or book, we are all convinced that there is a reality out there, just as we perceive it. And in real life, we do make a difference between things we know for certain, and things we merely believe to be true. So, yes, in that sense the claim that nothing is certain (except, for one;s own consciousness) is a pretty 'absurd' claim.

Also, before you edited your question, you called the claim 'depressing'. And sure, yes, the claim is also 'depressing' in the sense that as human beings we like certainty, and this claim says that almost nothing is certain.

OK ... but so what? Especially given your claim that "I really don't understand why philosophers would say that ..." I get the feeling that you're trying to argue as follows: "The claim that we may not be certain of anything existing except one's own consciousness is absurd and depressing. Therefore, the claim is false"

But this is surely a fallacy! I mean, if true, climate change is depressing .. but that does not mean it's not true. Lots of absurd things happen in quantum mechanics, but that does not make it false.

In short, things are absurd, depressing, and true, possibly including the claim you're focusing on.

Finally, I completely agree that

we can't be 100% certain of anything because we don't know everything.

is a really bad argument. That's like saying: "Not everything is an apple. Therefore nothing is an apple." It's a real shame that you were not told any better argument. In fact, I don't know any serious philosopher who makes that argument for the claim that nothing (except our own csns) is certain. The classic argument comes from Descartes, and that's a much better argument. Do you know it?


One classic argument is that I cannot be absolutely sure that I am not a brain in a vat, hooked up with wires to a computer sending signals into my brain. In this scenario, the computer provides me with a simulated environment that I think is reality but it really is not (think The Matrix). Unlike in The Matrix, though, the simulated environment could in principle be completely unlike reality; for example, maybe there is no such thing as gravity in reality. Hence, for almost anything, we cannot be absolutely sure it exists in reality. (However, it should be pointed out that David Chalmers has argued here that such a virtual reality would still be truly "real" in important ways.)

  • 1
    Yeah but, once you understand that it is impossible, namely it is impossible to create consciousness in a simulation of some sort. Shouldn't we all be sure 100% of reality? After that someone could always make any other absurd argument, but that has nothing to do with certainty at all.
    – user34482
    Aug 7, 2018 at 10:42
  • I agree it is conceivable that at some point we somehow conclude that it is impossible for consciousness to arise from a simulation (for some definition of a simulation), though today there is no consensus on that and in fact many people think that in principle it should be possible. However, the brain-in-a-vat scenarios don't require that we create consciousness. A pre-existing brain, already generating consciousness, can be put in a simulation. (The wikipedia page on brains in vats above lists some examples where it is just a relatively humdrum VR simulation.)
    – present
    Aug 7, 2018 at 17:38

You must log in to answer this question.