# Do you only know that you exist? **URL:** \ **Category:** Great Debates\ **Created:** [April 4, 2009, 6:40am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955 "2009-04-04T06:40:15Z")\ **Posts on this page:** 13\ **Page:** 4
**Author:** ![Frank\_Saxon](https://avatars.discourse-cdn.com/v4/letter/f/f17d59/32.png) [@Frank\_Saxon](https://boards.straightdope.com/u/Frank_Saxon)\ **Post date:** [April 9, 2009, 10:58am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/61 "2009-04-09T10:58:27Z")
Common sense should of course be leading in day to day activities. The next time I see a truck coming at me at great speed, I will choose to acknowledge its existence, or I might think myself in intensive care. You see, the truck doesn’t care whether I am a solipsist or not. On a more theoretical level though… The premise that we can’t trust our senses is wrong. If we can’t trust our senses, then we can’t trust our brain either. After all, the information coming from our senses is registered and processed in the brain. Why would the processing of sensory data be of any less value than the processing of logical data? The paradox exists only because we feel that our thought is of a higher level than our senses, which is false. On the flip side we could ponder what would happen if our sensitory data is correct, but our perception is wrong (actually a much more likely scenario). In that case, we will never know what hit us. ---
**Author:** ![begbert2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/begbert2/32/3357_2.png) [@begbert2](https://boards.straightdope.com/u/begbert2)\ **Post date:** [April 9, 2009, 4:11pm UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/62 "2009-04-09T16:11:35Z")
> [@Frank\_Saxon](#): > > Common sense should of course be leading in day to day activities. The next time I see a truck coming at me at great speed, I will choose to acknowledge its existence, or I might think myself in intensive care. > You see, the truck doesn’t care whether I am a solipsist or not. > > On a more theoretical level though… > > The premise that we can’t trust our senses is wrong. > If we can’t trust our senses, then we can’t trust our brain either. After all, the information coming from our senses is registered and processed in the brain. > > Why would the processing of sensory data be of any less value than the processing of logical data? > > The paradox exists only because we feel that our thought is of a higher level than our senses, which is false. > On the flip side we could ponder what would happen if our sensitory data is correct, but our perception is wrong (actually a much more likely scenario). > In that case, we will never know what hit us. Sensory data is meaningless if separated from our method of perceiving and interpreting it , so there is no functional difference between the signals coming into our brain omitting the truck, and our brains’ interpretation of the signals omitting the truck. Either way, we won’t know what hit us. 🙂 And why should the untrustworthiness of our thought processes contradict the premise that we can’t trust our senses? It’s like they say when somebody wonders whether a person is stupid or merely mistaken: why can’t it be both? ---
**Author:** ![Gabba\_Gabba\_Hey](https://avatars.discourse-cdn.com/v4/letter/g/ba8739/32.png) [@Gabba\_Gabba\_Hey](https://boards.straightdope.com/u/Gabba_Gabba_Hey)\ **Post date:** [April 10, 2009, 5:04am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/63 "2009-04-10T05:04:06Z")
> [@Half\_Man\_Half\_Wit](#): > > This appears contradictory – if there truly is nothing to think about without receiving any input, then you can’t hallucinate your own world in a solipsistic manner, since there exists nothing else to give you any input; if, on the other hand, you are able to create the hallucination of the world from nothing, then you get something to think about without ever having received sensory input. So either there must exist something besides you, or you must be able to think without ever receiving any stimuli; and in both cases, it seems to me, you know the appearance of other things. OK, I think you’re right about that. Even if existence caused illusions, you could say that you also know some_thing_ (in this case the act of existing) is causing the stimuli. Of course, now I’m wondering if you can know more than two things…:smack: I’m not sure I agree with you on knowing something that is basically imagined. An earlier poster (can’t remember who) made a good point in that the first step in this argument should be to define what it means to “know” something. ---
**Author:** ![Gabba\_Gabba\_Hey](https://avatars.discourse-cdn.com/v4/letter/g/ba8739/32.png) [@Gabba\_Gabba\_Hey](https://boards.straightdope.com/u/Gabba_Gabba_Hey)\ **Post date:** [April 10, 2009, 5:57am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/64 "2009-04-10T05:57:40Z")
> [@begbert2](#): > > It doesn’t, at all, because math and logic _are_ made up. Seriously. How many ‘fours’ do you see wandering the earth? Not collections of four items - not symbols that _represent_ “four” - but the abstract concept ‘four’ itself? Whoops, I said it: it’s abstract. It’s nothing but an idea, which has the mind as its native environment. > > So it doesn’t matter if you just made them up. All that matters is that you know their definitions, which are just ideas. From the definitions, the entire systems based on them follow. > > Which is not to say you can’t make errors and be wrong about your conclusions, but errors like that can be determined and ousted by sheer mental examination, which is possible form a solipsistic perspecive, so I don’t see how it’s a significant problem. (Assuming time is actually passing, anyway, but even if it’s not, the fact that you don’t know something doesn’t mean it’s not _knowable_.) Like I said in the above post to Half Man Half Wit, I should have defined “knowing” something first. To me, you know something only when you can prove it in the “real world.” I don’t know an idea because I could always change it, making it into another idea. Technically, nobody really knows how to speak English, because they could always encounter a slang word they’d never heard before. But, like I said, it depends on how you define “know.” ---
**Author:** ![begbert2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/begbert2/32/3357_2.png) [@begbert2](https://boards.straightdope.com/u/begbert2)\ **Post date:** [April 10, 2009, 6:08pm UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/65 "2009-04-10T18:08:34Z")
> [@Gabba\_Gabba\_Hey](#): > > Like I said in the above post to Half Man Half Wit, I should have defined “knowing” something first. To me, you know something only when you can prove it in the “real world.” I don’t know an idea because I could always change it, making it into another idea. Technically, nobody really knows how to speak English, because they could always encounter a slang word they’d never heard before. But, like I said, it depends on how you define “know.” The lovely thing about purely abstract systems like math is that if you can prove them anywhere, you can prove them in “the real world” too - because all the steps of the proof are portable. The definitions of “2”, “4”, etc don’t change whether you’re operating in your head, in a mirage, in a simulation, or the real world - so the proofs based on these definitions work equally well too. Of course, a relevent question is, is the abstract system in question _relevent_ to the world in question. Sometimes the answer is no - but that doesn’t make the mathematical system invalid, or even necessarily slow us down from using it! Take, for example, the formula for calculating the circumferance of a circle. C = 2_pi_r. Well, this is all well and good in abstract geometry, where circles are perfectly round. But in the real world, _no_ circles are truly perfectly round. Which _technically_ makes the circumferance formula inapplicable to the “real world”. (Of course, the error of the circumferance formula decreases as the near-circle gets closer and closer to an _actual_ circle, so we use the formula anyway and live with the errors.) So yeah, sometimes purely abstract systems don’t mesh well with reality - but that doesn’t stop them from being true in those realities, and even useful in some cases. ---
**Author:** ![Alan\_Smithee](https://avatars.discourse-cdn.com/v4/letter/a/2acd7d/32.png) [@Alan\_Smithee](https://boards.straightdope.com/u/Alan_Smithee)\ **Post date:** [April 11, 2009, 3:51am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/66 "2009-04-11T03:51:04Z")
Here’s another paradox in your system. Suppose you are correct that you can only know one thing, namely that you exist. If you have good reason to believe that you can only know one thing and believe it correctly then by most definitions you know a second thing: _that you can only know one thing._ In which case, it is false. QED. You might object that knowing that you can only know one thing is a trivial case that doesn’t really count as knew knowledge. But you have people here who don’t believe that you can know only one thing. If you are correct then you know something they don’t in a meaningful sense, so the proposition _You can only know one thing_ is a non-trivial object of knowledge. And again, necessarily false. ---
**Author:** ![dropzone](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dropzone/32/7515_2.png) [@dropzone](https://boards.straightdope.com/u/dropzone)\ **Post date:** [April 11, 2009, 5:33am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/67 "2009-04-11T05:33:49Z")
Do I really have to slog through the whole thread to comment? Yeah, since it’s GD? SCREW THAT! 😉 It’s all how you operate. Me? I operate as if my perceptions are (mostly) real (an ongoing case of clinical depression leaves a backdoor). Regarding others? I’ve learned that my world is less confusing if I accept them as real, except the obvious bullshit (ie: orbs, poisonous contrails). What others believe? Let them explain it and maybe I’ll listen, at least until I can find a search engine. But I will try to go along, because it’s polite. IOW, anybody who tries to prove he exists should try to accept that, if he has it together enough to ask, there might be something to it. IOOW, Dayam! I was a college freshman 36 years ago, but the children of my peers are still asking the same stupid questions! To quote the bygone antidrug ad, “Why do you think they call it dope?” ---
**Author:** ![Kozmik](https://avatars.discourse-cdn.com/v4/letter/k/8dc957/32.png) [@Kozmik](https://boards.straightdope.com/u/Kozmik)\ **Post date:** [April 11, 2009, 7:39am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/68 "2009-04-11T07:39:07Z")
I know I exist and I know someone else (hypothetically) exists. I’m me. I’m the guy who will ask such questions as: what if you take it too seriously and “pretend” (notice ‘air-quotes’) that it, whatever it is and whatever is is, isn’t, whatever, eh… ok? 😕 … five years later (what is time?)😕😕 hmmmm…(what does hmmmm mean?) [gasp](http://www.youtube.com/watch?v=rJ-QGLlniLM) :eek::eek::eek: ---
**Author:** ![ITR\_champion](https://avatars.discourse-cdn.com/v4/letter/i/c67d28/32.png) [@ITR\_champion](https://boards.straightdope.com/u/ITR_champion)\ **Post date:** [April 11, 2009, 8:34am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/69 "2009-04-11T08:34:47Z")
> [@Gabba\_Gabba\_Hey](#): > > Two things: > > Point Number One: “The answer is that St. Thomas recognised instantly, what so many modern sceptics have begun to suspect rather laboriously; that a man must _either_ answer that question in the affirmative, or else never answer any question, never ask any question, never even exist intellectually, to answer or to ask.” I put “either” in italics to point out that Aquinas admits there is a choice between the two. He still can’t prove one over the other. We “assume” the exterior world is real, because to do otherwise leads to intellectual paralysis, at best a kind of mental masturbation.\* Chesterton says we should go by common sense, but didn’t common sense tell us that the Earth is flat, that a plague was punishment from the gods, or that George W. Bush was a competent, capable leader? The argument can be taken too far, but isn’t it good to stop every once in a while and remind yourself that the things you “know” are only assumptions? If you don’t believe me, check out the movie Rashomon. If you still don’t believe me, ask the guys who went to prison on rape charges through the eyewitness testimony of the victims and were later exonerated by DNA evidence. > > Point Number Two: POINT NUMBER ONE WAS NEVER MY MAIN ARGUMENT!!! OK, sorry to yell, but I really wanna know if I’m right or wrong. My whole argument boils down to this: if I am right, no matter how much you study/read/learn you only know _one_ fact - that you exist. I’m not saying only I exist, but that I only know one fact. I’ve heard the whole solipsism thing before. Anyone who has taken a freshman philosophy class has. But I’ve never heard it described as “You only know one thing” (which I, personally, think would sound cool on a T-shirt). That’s why I was hoping the SD’ers could help. If you know more than one thing, what it it? Can you prove that mathematics is correct without an external world? What about logic? Anything? Folks, please give me an answer! I think that the three paragraphs I chose may not have been quite sufficient to illustrate what Chesterton was trying to say about Aquinas. Chesterton’s point was this. First, there is a body of philosophical conclusions that the “man in the street” would recognize as “common sense”. Second, that all the major modern philosophers have reached conclusions that contradict some part of this “common sense”. Third, that Thomas Aquinas was the philosopher who would most closely agree with common sense. However, Aquinas does not argue from common sense. He does not say that certain conclusions must be true because they are part of common sense. Aquinas argued from rational assumptions, using logical deductions. Chesterton’s only point is that the logical conclusions that Aquinas arrives at are common sensical. (I know it’s not a word, but it should be.) As for what Aquinas’ argument actually is, I’m afraid that I can’t say. I’ve only read small portions of the _Summa Theologica_, and while I’d like to go deeper at some point, I know that it’s rough going. Based on the summaries I’ve read, it sounds as if Aquinas’ argument may be somewhat similar to the one that **Half Man Half Wit** is using here, namely starting from the knowledge of the self, one knows that there is a state of existence, and we can expand outwards from there. But really, my only point in posting was to inform you that Aquinas had tackled the issue. I can’t claim to successfully lead you beyond that. ---
**Author:** ![ITR\_champion](https://avatars.discourse-cdn.com/v4/letter/i/c67d28/32.png) [@ITR\_champion](https://boards.straightdope.com/u/ITR_champion)\ **Post date:** [April 11, 2009, 9:16am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/70 "2009-04-11T09:16:36Z")
> [@Revenant\_Threshold](#): > > It’s my personal opinion that we can’t even be sure we exist, so that may very well colour my responses. As far as I can tell, if my reading of Chesterton’s summary is correct, Aquinas offers no refutation at all for that particular premise. Aquinas points out that if we cannot be sure that our recognition of reality is correct, then we can make no further premises or guesses; that it’s a philosophical dead end, and if we accept it, we can’t then say anything else at all about reality. And I would agree. But that’s not a refutation; it’s not saying that it isn’t the case, it’s saying that should it be the case, here are the results of that - not pleasant results if we care about philosophical inquiry, certainly, but they are _results_, of a possibility. > > When he goes on to point out why exactly Aquinas believes this view to be false, he suggests it is because Aquinas is one for selecting the “obvious” answer, the result of common sense, and of simplicity. Reality is as we percieve it because that’s the more clear way of thinking - to drag in Occam, it’s not multiplying entities unnecessarily. The problem with using that in this particular line of theory of course is that we are postulating the existence of the intial (and every other) entity in the first place. If Chesterton’s analysis is correct (and my reading of it is, also), then Aquinas is using the conclusions to support his premise. Trying to elaborate a bit further, I don’t think that the argument rests on simplicity or clarity. Rather, it rests only on the existence of a valid set of rules that constitute logic. Now is the existence of such a set of rules in question? **Gabba Gabba Hey** has gone so far as to question the validity of basic arithmetic in the exterior world. But it’s telling that in his original post, he started by saying “_If you really think about it_, the only thing you truly know is that you exist.” (Emphasis mine.) So right there, he has admitted that there is such a thing as thought. Moreover, he also seems to acknowledge that some thoughts are valid and other thoughts are not valid. If we can all agree on that much, then let’s consider what happens if we pursue **Gabba Gabba Hey** ’s line of reasoning. As it happens, this was a topic that Chesterton took on himself in a chapter of _Orthodoxy_ called [The Suicide of Thought](http://www.ccel.org/ccel/chesterton/orthodoxy.vi.html). The conclusion is summarized in the title. If a person insists on being so totally so totally reductive–as **Gabba** is–then eventually the line of reasoning recoils and destroys itself. How could he even know that he only knows of his own existence, if he won’t accept some thoughts as absolutely valid? ---
**Author:** ![Grumman](https://avatars.discourse-cdn.com/v4/letter/g/43a26b/32.png) [@Grumman](https://boards.straightdope.com/u/Grumman)\ **Post date:** [April 11, 2009, 9:58am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/71 "2009-04-11T09:58:51Z")
> [@begbert2](#): > > It doesn’t, at all, because math and logic _are_ made up. Seriously. How many ‘fours’ do you see wandering the earth? Not collections of four items - not symbols that _represent_ “four” - but the abstract concept ‘four’ itself? Whoops, I said it: it’s abstract. It’s nothing but an idea, which has the mind as its native environment. It’s an attribute (of a group of things) rather than a thing itself, but that doesn’t mean it’s made up. ---
**Author:** ![flonks](https://avatars.discourse-cdn.com/v4/letter/f/3ab097/32.png) [@flonks](https://boards.straightdope.com/u/flonks)\ **Post date:** [April 11, 2009, 6:48pm UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/72 "2009-04-11T18:48:17Z")
According to [this paper](http://www.simulation-argument.com/simulation.pdf), we might all live in a simulation … ---
**Author:** ![Revenant\_Threshold](https://avatars.discourse-cdn.com/v4/letter/r/f1d935/32.png) [@Revenant\_Threshold](https://boards.straightdope.com/u/Revenant_Threshold)\ **Post date:** [April 11, 2009, 8:02pm UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/73 "2009-04-11T20:02:44Z")
> [@ITR\_champion](#): > > Trying to elaborate a bit further, I don’t think that the argument rests on simplicity or clarity. Rather, it rests only on the existence of a valid set of rules that constitute logic. Now is the existence of such a set of rules in question? **Gabba Gabba Hey** has gone so far as to question the validity of basic arithmetic in the exterior world. But it’s telling that in his original post, he started by saying “_If you really think about it_, the only thing you truly know is that you exist.” (Emphasis mine.) So right there, he has admitted that there is such a thing as thought. Moreover, he also seems to acknowledge that some thoughts are valid and other thoughts are not valid. I don’t think that’s particularly telling; i’m not a huge fan of wording “gotchas”, since generally we’re not exactly hugely accurate when we use language. I would prefer to use “with the appearance of thought, the only thing…” and even that i’d question, since while it was true for me once it not longer is (i’ve already had that appearance, after all) and for others it may take shorter or longer to catch onto the idea. I do question the existence of basic rules of logic, both that they exist at all and that they exist as we know them. We can’t know they exist, because if they don’t, then it’s quite possible our tools to know this will return incorrect results. You can’t measure the accuracy of a ruler with the ruler itself. > [@](#): > > If we can all agree on that much, then let’s consider what happens if we pursue **Gabba Gabba Hey** ’s line of reasoning. As it happens, this was a topic that Chesterton took on himself in a chapter of _Orthodoxy_ called [The Suicide of Thought](http://www.ccel.org/ccel/chesterton/orthodoxy.vi.html). The conclusion is summarized in the title. If a person insists on being so totally so totally reductive–as **Gabba** is–then eventually the line of reasoning recoils and destroys itself. How could he even know that he only knows of his own existence, if he won’t accept some thoughts as absolutely valid? The line of reasoning doesn’t destroy itself - rather, it may destroy itself, but like everything else, we simply do not know. I don’t believe we know we exist, again either totally or as we believe ourselves to be. To take one example, you believe in free will, I believe, whilst I do not; one of us is incorrect in our knowledge of ourselves, if our understanding of logic is correct or is wrong but happens to return that result anyway. I accept no thoughts as absolutely valid. To the extent that I accept relative validity, it is because it appears at least to keep up with appearances, but as shown, appearances vary wildly between different people (if there are different people, or people at all ;)), so even that is entirely personal, if there is a me for it to be personal for. Everything is questionable; there are no certainties, except of course that there might be. [Previous page](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955.md?page=3)