## Is it possible to be 100% certain of the existence of reality?

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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. – None – 2018-08-06T17:17:15.993

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 – 2018-08-06T17:21:27.807

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 – 2018-08-06T17:24:55.327

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. – None – 2018-08-06T17:28:43.197

The post is not about uselessness of extreme skepticism. It's rather about the wrongness of it. – None – 2018-08-06T17:33:29.147

Ah! OK, so my first interpretation was correct after all. Well, did you read my post? Claims can be absurd and depressing, but neither of that means the claims is false. – Bram28 – 2018-08-06T17:40:22.783

I see you made an edit.... but reading your post now you simply seem to deny the claim and not even attempt to give any argument at all. It's like: "They say this. I don't believe it. What do you think?". Well, I think that's not a very good question. I also think that in order for this to be a good question, you at least should make an attempt at an argument. Maybe you could try and argue how you are certain that gravity exists? – Bram28 – 2018-08-06T17:48:57.500

I believe it's false and I added depressing because it is and I was wondering if I was the one looking at it in the wrong way. I would rather focus on the wrongness or truthfulness of the claim. Maybe it's just me looking at it in the wrong way. I can say though that I am still not 100% certain of its wrongness. – None – 2018-08-06T17:53:09.733

Got it. Well, I personally believe it is true that very few things are 100% certain. (I also believe that plenty of things are 99.9999999% certain, but I suppose that's not the claim of interest). And, having read Descartes' argument, and just having been around long enough and having seen how often humans think something is true when it isn;t, the claim is no longer absurd to me. Indeed, i now believe it would be absurd if humans would be able to know things with absolute certainty. And finally, none of this is depressing to me. In most cases, 99.999.% certainty is good enough. :) – Bram28 – 2018-08-06T17:57:29.263

Ok, but there is literally people who claim that you can only know with 99.99999% probability that Descartes and humans actually exist. Isn't that just a wrong way of looking at what we don't know? – None – 2018-08-06T18:09:25.333

But even if Descartes never existed, I still think there is strength in the argument. Arguments don't fall or stand relative to whoever makes the argument. – Bram28 – 2018-08-06T18:20:41.197

What is reality? Try hiding an object where you know someone will find it and return it to you at an unspecified point in the future. It's satisfying.. reassuring. I was once about as monist, reductionist.... Scientific as it's possible to be. But as I've aged my concept of reality has become much less certain. I know that my current state of mind would be anathema to my younger self.. but that makes me wonder about the effect my younger self's hormones had on by certainty of universal reality. Rationally I believe my current state in error.. but there it is. – Richard – 2018-08-06T23:25:03.470

What do you mean by "certain?" The question you are exploring is a very good one, but the words are tricky. The most accepted wordings I know of are discussed in the SEP article on Knowledge. It uses the term "knowledge" rather than certainty, but I think that's the concept you're digging at. I like the use of the word "know" rather than "certain" because certainty is more associated with belief, and knowledge is typically given additional implications beyond belief, as is discussed in the article.

– Cort Ammon – 2018-08-07T01:20:19.097

(on the note about "depressing," I find it to be the very opposite of depressing. The way I use "certain" in my own life is intrinsically limited by language because that's how I think about it. To know that even if I am "certain" of something, it can surprise me is something I find desirable. It brings up the possibility that reality is not limited to the confines of the things I can be certain about) – Cort Ammon – 2018-08-07T01:23:16.983

@CortAmmon By "certain" I mean: I don't need to just believe at something, I know it's true and undoubtable. But what is that something? In my opinion there are many things including reality, but radical skeptics would say that the only thing absolutely certain is my ego. I don't agree with them. It seems to me that they are overrating the unknown so that what we already know lacks of certainty. E.g: We cannot be 100% certain of the existence of reality because we might live in a dream. Reality is not 100% certain just because someone created an argument based on no evidence. I don't buy it. – None – 2018-08-07T11:38:40.747

Are you looking for a bunch of people to agree with you, or are you looking to explore both sides? For example, a standard line of reasoning for skeptics is that of the Münchhausen trilemma. For a skeptic, having a logical proof that I know something which is dependent upon a self-evident truth is unsatisfying, so "I don't buy it." For other individuals, it may be acceptable that there are self-evident truths (or irreducible circular arguments, etc.) and for them, the skeptic's claims appear unfounded.

– Cort Ammon – 2018-08-07T14:15:27.583

I could put an answer together from that perspective if you feel its a direction which might satisfy your question. (I'm trying to steer it away from "What do you think," which is too opinion based for a SE question) – Cort Ammon – 2018-08-07T14:26:43.970

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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 – 2018-08-08T01:50:18.447

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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. – Frank Hubeny – 2018-08-06T19:55:11.303

"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? – David Thornley – 2018-08-06T22:50:05.220

thanks @frank-hubeny, there are many references in our philosophy like Bu-Ali Sina philosophy or Mulla Sadra's philosophy . – Hossein Vatani – 2018-08-07T00:10:49.323

@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?. – Hossein Vatani – 2018-08-07T00:32:15.863

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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?

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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.)

1Yeah 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. – None – 2018-08-07T10:42:28.220

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 – 2018-08-07T17:38:38.377