# 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:** 20\ **Page:** 2
**Author:** ![Indistinguishable](https://avatars.discourse-cdn.com/v4/letter/i/90ced4/32.png) [@Indistinguishable](https://boards.straightdope.com/u/Indistinguishable)\ **Post date:** [April 5, 2009, 3:30am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/21 "2009-04-05T03:30:55Z")
> [@The\_Tao\_s\_Revenge](#): > > Consider the color **blue**. Now what if your brain had an odd quirk and **blue** looked **red** to you and red looked blue to you. Meaning anything you saw that was **red** was really **blue** to everyone else, and **blue** was really **blue** to everyone. Swapped just like that. Seems like that last “ **blue** ” should be changed to “ **red** ”, no? Anyway, my response to this sort of worry would be to say that it is meaningless to ask whether my “private” sensation of blue is the same as yours; there is no custom in our language-defining behavior which would give sense to such an investigation. So there is no question as to whether there is an undetectable mismatch between my color sensations and everyone else’s, any more than there is some question as to whether, say, we’ve all collectively been misled as to the definition of the word “dog”, the word actually referring to a small species of tree. [Hm, maybe that’s not the best analogy, but it’s what came to mind]. The fact that I, in my public behavior, make such color judgements as conform with everyone else is, in itself, all there is to my qualia matching theirs. I would say I find some support for this view in Wittgenstein’s so-called “private language argument(s)”, but then, everyone feels they find some support for their view in there, whatever their view is… ---
**Author:** ![Indistinguishable](https://avatars.discourse-cdn.com/v4/letter/i/90ced4/32.png) [@Indistinguishable](https://boards.straightdope.com/u/Indistinguishable)\ **Post date:** [April 5, 2009, 3:40am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/22 "2009-04-05T03:40:33Z")
> [@Gabba\_Gabba\_Hey](#): > > I have only a vague knowledge of Descartes but I’m well aware he came up with this and that there’s no way to truly know whether the external world is real. What I’m arguing is that “I think therefore I am” is the _only_ thing you can truly know. That’s why I brought up the stuff about mathematics, causality, etc… Yes, that was also Descartes’ point with it; maximum skepticism, not just about empirical matters, but about anything and everything possible. But no problem; I didn’t mean to attack you for having an idea independently (heck, everyone _should_ have these thoughts on their own at some point), but merely to help guide you towards what kind of commentary you might want to look for if you’d like to see what ideas others have had on the subject. (In fact, don’t get me wrong, I am not at all recommending that you should read the Descartes; in the next chapter, it gets weak, and after that, it goes totally off the rails. I am just pointing out that, should you wish to look at it, there have been oodles of commentary written in response to this idea from every which perspective over the past several centuries.) Anyway, as far as my own commentary goes, I’d still like to know what your response to the question I posed in [post #4](http://boards.straightdope.com/sdmb/showpost.php?p=11004993&postcount=4) is? ---
**Author:** ![Dallas\_Jones](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dallas_jones/32/3277_2.png) [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)\ **Post date:** [April 5, 2009, 3:56am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/23 "2009-04-05T03:56:09Z")
You should read the 2 short stories They, and All you Zombies by R. A. Heinlein. Then you will see that even you, and this board, exist only to entertain me. If I cease to be interested, you all cease to exist. Anyway, they are a couple good stories. ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [April 5, 2009, 6:30am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/24 "2009-04-05T06:30:09Z")
I _am_ a solipsist. . . . but nobody agrees with me. ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [April 5, 2009, 12:46pm UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/25 "2009-04-05T12:46:24Z")
The voices tell me I’m all alone… ---
**Author:** ![WhyNot](https://avatars.discourse-cdn.com/v4/letter/w/c77e96/32.png) [@WhyNot](https://boards.straightdope.com/u/WhyNot)\ **Post date:** [April 5, 2009, 1:10pm UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/26 "2009-04-05T13:10:52Z")
> [@Gabba\_Gabba\_Hey](#): > > I probably didn’t explain my position as well as I should have , so let me try again. I’m in no way claiming I created cogito ergo sum\*. I have only a vague knowledge of Descartes but I’m well aware he came up with this and that there’s no way to truly know whether the external world is real. What I’m arguing is that “I think therefore I am” is the _only_ thing you can truly know. That’s why I brought up the stuff about mathematics, causality, etc… Put another way, do you know anything (logically speaking) other than that you exist? > > \*: In my defense, however, I am the creator of the First Discount Church of God: the only religion which promises eternal salvation for the low, low price of $9.95. Please don’t feel bad that you didn’t come up with this first. I hate it when people jump all over a person for that. True, this is not an original thought in the history of mankind, but it is an interesting and large bit of philosophy to come up with on your own, and you shouldn’t be undercut for your efforts simply because others did so as well. Secondly, it might be worth remembering that, scientifically speaking, we can never prove anything; we can merely \*disprove \*hypotheses. We can be pretty damn sure the sun will rise tomorrow, we can be almost certain this glass will shatter if I drop it, we can be nearly positive that gravity is a constant, but we can never prove so. All we can do is say that, so far, any experiments with the hypothesis in favor of gravity have been borne out and all hypotheses that objects will float when you let go of them (on Earth, not in water or on other planets) have not borne that out. We have disproven that things always float when you let go of them on Earth, but we can never prove that things won’t ever float. It’s terribly unlikely that they ever will, based on how many “experiments” we perform every day where things don’t float, but things are never proven in the affirmative, only the negative. So, beyond the solipsistic reasoning, there’s a larger scientific logic that says you can never prove anything to be, you can only prove it isn’t. In other words, yes, I agree. I only know that I exist (and, to be honest, I’m a little uncertain about that sometimes). But my life, or that which I interpret to be as my life, feels better to me as if I act as if other people and creatures exist. To paraphrase the Man in The Shack, aka, The Ruler of the Universe (a character in Douglas Adams’ _The Restaurant at the End of the Universe_) “I only know that I exist. I am my own universe of my eyes and my ears. . . It merely pleases me to behave in a certain way to what appears to be a cat. What else do you do?” ---
**Author:** ![Tibby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tibby/32/17030_2.png) [@Tibby](https://boards.straightdope.com/u/Tibby)\ **Post date:** [April 5, 2009, 5:39pm UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/27 "2009-04-05T17:39:31Z")
I’m sorry Gabba Gabba Hey, but the evidence taken in toto does not warrant the conclusion that solipsism is correct—at best it merely introduces a healthy dose of skeptisim. At the very least, solipsism is a false philosophical theory, perhaps even necessarily foundationless in theory and fact. But, of course, the coup de grâce to both solipsism and Cartesian dualism is a package of arguments, often called the “private language argument”…they…uh…oh fiddle sticks… _…Stranger, Indistinguishable, Nemo, Tao’s, WhyNot_, et al…do you guys mind if I spill the beans? The big kahuna’s starting to catch on, and I for one am growing weary keeping this inveracity alive. I really think the jig’s up. So, if you don’t mind… …_Gabba Gabba Hey_, you exist. And, in fact, you’re the only one who does exist. We’re just here to keep you from going a little bonkers being all alone in this vast Universe…_Well, there I go again—the lies come easy after a while_— unless you consider an enclosed space extending a few miles past the farthest place you’ve traveled to be a vast universe (did you ever examine those celestial bodies in the sky, closely?—just dots of Eggshell White Glidden paint splattered on black muslin. A guy named Ralph (well, technically another faux-guy of your own mental construction) paints all those Hubble photos. Things were ok in the beginning. Not too many faux-beings cluttering things up. We (by “we”, I mean “you”…your mind…your brain on bugs) just had to fabricate “mom”, then a few other “family” members, neighborhood “friends”, grade school teachers…”Billy”, that bully who used to pull down your pants and make you sing “I’m a LIttle Tea Pot” in front of the girl’s locker room. Not too hard to keep track of—and kind of fun…But, then you had to grow up, didn’t you? The good-hearted, uni-dimensional “people” (and “pets”…you didn’t think ol’ _Bosco_ was real, did you?) of your childhood just weren’t enough to keep you occupied. You had to add more and more, stranger and stranger pseudo-people to your mental menagerie. I mean, we thought you were pushing the envelope a little with that chick with the Ben Wa balls and her toothless mongoose… but Paris Hilton?..Michael Jackson?..Paulie Shore? Dude! C’mon, what were you thinking!?! Indeed, my cohorts in crime and I have known all along that we’re simply constructs of your warped little mind—and, yes, it does kind of suck being mere bit players in the theater of your hyper-active imagination. So, I for one hereby tender my resignation. More will follow. Soon, you’ll know exactly what it means to be alone in the Universe. But, please, don’t blame us; you’ve got no one to blame…but yourself. ---
**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 5, 2009, 6:46pm UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/28 "2009-04-05T18:46:36Z")
> [@Gabba\_Gabba\_Hey](#): > > He still disagrees, so I ask, can you sort this out, Cecil? Is my premise correct? Or should I just cut back on the weed? > > -Your pal Mike I don’t think that your premise is correct at all. I believe that the best refutation of what you claim was the one written by St. Thomas Aquinas. The actual argument as written by Aquinas is too long to be posted here, but I’ll offer the [a summary of the relevant portion](http://www.saintwiki.com/index.php?title=Chesterton:_Aquinas%2C_Chapter_VI) as written by Chesterton. > [@](#): > > Even those who appreciate the metaphysical depth of Thomism in other matters have expressed surprise that he does not deal at all with what many now think the main metaphysical question; whether we can prove that the primary act of recognition of any reality is real. 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 suppose it is true in a sense that a man can be a fundamental sceptic, but he cannot be anything else: certainly not even a defender of fundamental scepticism. If a man feels that all the movements of his own mind are meaningless, then his mind is meaningless, and he is meaningless; and it does not mean anything to attempt to discover his meaning. Most fundamental sceptics appear to survive, because they are not consistently sceptical and not at all fundamental. They will first deny everything and then admit something, if for the sake of argument–or often rather of attack without argument. I saw an almost startling example of this essential frivolity in a professor of final scepticism, in a paper the other day. A man wrote to say that he accepted nothing but Solipsism, and added that he had often wondered it was not a more common philosophy. Now Solipsism simply means that a man believes in his own existence, but not in anybody or anything else. And it never struck this simple sophist, that if his philosophy was true, there obviously were no other philosophers to profess it. > > To this question “Is there anything?” St. Thomas begins by answering “Yes”; if he began by answering “No”, it would not be the beginning, but the end. That is what some of us call common sense. Either there is no philosophy, no philosophers, no thinkers, no thought, no anything; or else there is a real bridge between the mind and reality. But he is actually less exacting than many thinkers, much less so than most rationalist and materialist thinkers, as to what that first step involves; he is content, as we shall see, to say that it involves the recognition of Ens or Being as something definitely beyond ourselves. Ens is Ens: Eggs are eggs, and it is not tenable that all eggs were found in a mare’s nest. > > Needless to say, I am not so silly as to suggest that all the writings of St. Thomas are simple and straightforward; in the sense of being easy to understand. There are passages I do not in the least understand myself; there are passages that puzzle much more learned and logical philosophers than I am; there are passages about which the greatest Thomists still differ and dispute. But that is a question of a thing being hard to read or understand: not hard to accept when understood. That is a mere matter of “The Cat sat on the Mat” being written in Chinese characters: or “Mary had a Little Lamb” in Egyptian hieroglyphics. The only point I am stressing here is that Aquinas is almost always on the side of simplicity, and supports the ordinary man’s acceptance of ordinary truisms. For instance, one of the most obscure passages, in my very inadequate judgment, is that in which he explains how the mind is certain of an external object and not merely of an impression of that object; and yet apparently reaches it through a concept, though not merely through an impression. But the only point here is that he does explain that the mind is certain of an external object. It is enough for this purpose that his conclusion is what is called the conclusion of common sense; that it is his purpose to justify common sense; even though he justifies it in a passage which happens to be one of rather uncommon subtlety. The problem of later philosophers is that their conclusion is as dark as their demonstration; or that they bring out a result of which the result is chaos. ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [April 5, 2009, 10:54pm UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/29 "2009-04-05T22:54:07Z")
Regarding that whole solipsism deal – how are the entity that thinks (and therefore is) and the entity that gives rise to the outside world/creates its appearance identified? There’s a big hidden assumption in that: namely, that every conscious entity entails an unconscious one, and that both of them are, in fact, parts of one and the same being, which isn’t really a given once you neglect the existence of anything exterior to your own consciousness. In other words, there’s something that thinks – myself – and then there’s something that shows me an ‘outside world’ – yet, speaking from experience, it’s not something subject to my will, no matter how hard I try and make constipated faces. So how can that be said to be _me_, as well? One could postulate a more fundamental entity, part of which would be my consciousness, and part of which would be whatever it is that gives the appearance of an outside world to my consciousness, but that’s a definition that would pretty well be met by the universe, or whatever else you’d like to call the totality of being. So it seems to me that there’s more than we can know of than just our own existence – I do get all that data from what appears to be an outside world, and I don’t generate it voluntarily; so either there’s something external that generates this data, or I am just part of a greater whole, both of which necessitate the existence of something different from myself. ---
**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 6, 2009, 1:29am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/30 "2009-04-06T01:29:21Z")
> [@Indistinguishable](#): > > As one first objection to the particular position you’ve settled at, let me ask you this: you reject such reasoning as would establish 2 + 2 = 4 because you might only be dreaming that such reasoning is accurate, and will realize some error within it upon awakening. Well, isn’t it equally possible that you are only dreaming that “Logically speaking, if I don’t exist, there’s no one to think about the question.”, and when you wake, you’ll see some fallacy in this reasoning? What’s the distinction between these two cases? Just read your most recent post and, don’t worry, I didn’t take it personal. In fact I’d buy you a beer if I knew that you existed. Or the beer. Or…aw fuck it… In regards to the question above, I think there is a difference. Remember, in my original statement I said “If you _think_ about it, you only know you exist.” By thinking I, of course, mean logical thinking. If I wake and find logic different, I need to differentiate between the two. I’ll call them “Waking Logic” and “Dream Logic.” According to Waking Logic, I’m wrong. But when I said “If you think about it…” I was referring to Dream Logic. I just didn’t have the foresight to say “If you think about it in Dream Logic…” Later! ---
**Author:** ![The\_Tao\_s\_Revenge](https://avatars.discourse-cdn.com/v4/letter/t/73ab20/32.png) [@The\_Tao\_s\_Revenge](https://boards.straightdope.com/u/The_Tao_s_Revenge)\ **Post date:** [April 6, 2009, 3:37am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/31 "2009-04-06T03:37:16Z")
> [@Indistinguishable](#): > > Seems like that last “ **blue** ” should be changed to “ **red** ”, no? Yea I frelled up the edit request. By then I just gave up and went to bed. > [@](#): > > Anyway, my response to this sort of worry would be to say that it is meaningless to ask whether my “private” sensation of blue is the same as yours; there is no custom in our language-defining behavior which would give sense to such an investigation. So there is no question as to whether there is an undetectable mismatch between my color sensations and everyone else’s, any more than there is some question as to whether, say, we’ve all collectively been misled as to the definition of the word “dog”, the word actually referring to a small species of tree. [Hm, maybe that’s not the best analogy, but it’s what came to mind]. The fact that I, in my public behavior, make such color judgements as conform with everyone else is, in itself, all there is to my qualia matching theirs. > > I would say I find some support for this view in Wittgenstein’s so-called “private language argument(s)”, but then, everyone feels they find some support for their view in there, whatever their view is… Sounds like the document is an ink blot test. Sounds interesting though. The point I was trying to make though is we have to take on faith that the data our senses give us is accurate. I find it to be the sane practical assumption to make. At the same time recognizing people’s experiences are a subjective interpretation of their sensual data. consider the blindmen and a elephant [Blind men and an elephant - Wikipedia](http://en.wikipedia.org/wiki/Blind_men_and_an_elephant) 6 blind men are asked to feel and describe an elephant. One just grabs the trunk, one just grabs a leg, one just a tail, one an ear, one a tusk, and one grabs the body. The trunk grabber describes the elephant as a tree branch. The leg grabber describes the elephant as piller. The tail grabber says an elephant is like a rope. The ear grabber describes the elephant as a fan. The tusk grabber says the elephant is like a pipe, and the one who felt the body says the elephant is like a wall. The blind men start arguing because they all have different contradictory ideas about what an elephant is, and felt the elephant themselves and know for sure so the others must be wrong. Finally a wise man explains to them that they’re all right. They just explored different features of an elephant. I also remember hearing another story about a hat. I think it was an African story. One side of the hat was green, and the other red. A mean was wearing it walking along cause arguments about what color the hat was. The people who say the red side said it was red, unlike those delusional heathens who say it was green. ---
**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 6, 2009, 4:03am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/32 "2009-04-06T04:03:17Z")
> [@ITR\_champion](#): > > I don’t think that your premise is correct at all. I believe that the best refutation of what you claim was the one written by St. Thomas Aquinas. The actual argument as written by Aquinas is too long to be posted here, but I’ll offer the [a summary of the relevant portion](http://www.saintwiki.com/index.php?title=Chesterton:_Aquinas%2C_Chapter_VI) as written by Chesterton. 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! \*:which, through rigorous testing, I have determined is far inferior to the physical kind. Ahem. ---
**Author:** ![Indistinguishable](https://avatars.discourse-cdn.com/v4/letter/i/90ced4/32.png) [@Indistinguishable](https://boards.straightdope.com/u/Indistinguishable)\ **Post date:** [April 6, 2009, 4:06am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/33 "2009-04-06T04:06:21Z")
> [@Gabba\_Gabba\_Hey](#): > > In regards to the question above, I think there is a difference. Remember, in my original statement I said “If you _think_ about it, you only know you exist.” By thinking I, of course, mean logical thinking. If I wake and find logic different, I need to differentiate between the two. I’ll call them “Waking Logic” and “Dream Logic.” According to Waking Logic, I’m wrong. But when I said “If you think about it…” I was referring to Dream Logic. I just didn’t have the foresight to say “If you think about it in Dream Logic…” So you _know_ that you exist, because you can demonstrate so from Dream Logic (by which I mean, whatever logic is currently in your head)? Well, presumably, you can also demonstrate that 2 + 2 = 4 from Dream Logic as well. So, is it not the case that you analogously _know_ that 2 + 2 = 4? ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [April 6, 2009, 8:29am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/34 "2009-04-06T08:29:47Z")
> [@Gabba\_Gabba\_Hey](#): > > 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? Well, you know how a lot of things seem to be – how red looks, how skin feels, things like that. That you don’t (and can’t) know whether that’s how those things actually are, or even whether or not they are at all, doesn’t to me seem to contradict your subjective experiences of the outside world being knowledge. After all, it’s true that things seem as they seem, regardless of whether or not they actually are as they seem; so you know, at least, the way things seem. I’m still not quite convinced by whole solipsism thing itself, by the way – if I start with ‘I think, therefore I am’, then I have established my own existence. However, I have also established the existence of something that creates the appearance of an outer world for my benefit, since the I that’s thought the thought appears to perceive that outer world. Now, it’s commonly assumed that this ‘builder’ is just an expression of the 'thinker’s subconscious – that the thinker feeds itself that outside appearance while in some way making itself unaware of this, while making itself unaware of making itself unaware, and so on and on --, but it’s nowhere been established that the thinker even has a subconscious; and even if it has one, it’s not clear to me how both are supposed to be, in some way, the ‘same thing’. If there’s a conscious part that does all the thinking, that makes decisions, does anything that you are, in short, conscious of; and if there’s an unconscious part that gives rise to all the phenomena of the outside world, possibly even to external constraints and compulsions on the conscious part; and if the conscious part can make no decisions that affect the unconscious part’s doing whatever it does, i.e. if the unconscious part is not subject to conscious will (and to a certain extent, even if the unconscious part obeys the conscious will – it might be aware of the thinker’s thoughts, and grant a wish, for example) – then I don’t see how both can be said to be the same in any way. ---
**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 6, 2009, 11:04am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/35 "2009-04-06T11:04:27Z")
> [@Indistinguishable](#): > > So you _know_ that you exist, because you can demonstrate so from Dream Logic (by which I mean, whatever logic is currently in your head)? Well, presumably, you can also demonstrate that 2 + 2 = 4 from Dream Logic as well. So, is it not the case that you analogously _know_ that 2 + 2 = 4? No, because I still don’t know that the external world is real. Dream Logic (i.e. conventional logic) says that that which performs an action must exist in at least some form. I don’t need access to the “real” world to prove it because it’s true by definition. If I say, imagine there’s a boy named Billy who is seven years old, you will never be able to disprove that Billy is seven. It’s true because we agreed upon it. That’s why I was careful to say “_If you think about it…_” By entering into the argument, I’m forcing you to use conventional logic. Ain’t I a stinker? ---
**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 6, 2009, 12:20pm UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/36 "2009-04-06T12:20:49Z")
> [@Half\_Man\_Half\_Wit](#): > > Well, you know how a lot of things seem to be – how red looks, how skin feels, things like that. You know how things _seem_ to be, but you still don’t know whether they’re real or illusion. You could argue you know you experience sensations (sights, smells, etc…), but, to me, that just sounds like another way of saying you know you exist. In order to know _anything_, you must be receiving input with which to reach a conclusion. If you didn’t have any input, you’d be a vegetable, unaware of your own existence, because there’s nothing for you to think about. Saying you know you experience sensations is the same as saying you know you experience sensations which proves you exist. > [@Half\_Man\_Half\_Wit](#): > > I’m still not quite convinced by whole solipsism thing itself, by the way – if I start with ‘I think, therefore I am’, then I have established my own existence. However, I have also established the existence of something that creates the appearance of an outer world for my benefit, since the I that’s thought the thought appears to perceive that outer world. Not really. The sensations you experience could be illusions coming from your own subconscious (though I don’t know how), or they could be external but still not real (aliens have put your brain in a jar, and are feeding them to you), or _maybe they just exist._ Maybe the universe is just a big ball of illusions. You don’t know that anything or anyone is creating them, because they could exist independently. ---
**Author:** ![Indistinguishable](https://avatars.discourse-cdn.com/v4/letter/i/90ced4/32.png) [@Indistinguishable](https://boards.straightdope.com/u/Indistinguishable)\ **Post date:** [April 6, 2009, 5:22pm UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/37 "2009-04-06T17:22:47Z")
> [@Gabba\_Gabba\_Hey](#): > > No, because I still don’t know that the external world is real. Dream Logic (i.e. conventional logic) says that that which performs an action must exist in at least some form. I don’t need access to the “real” world to prove it because it’s true by definition. If I say, imagine there’s a boy named Billy who is seven years old, you will never be able to disprove that Billy is seven. It’s true because we agreed upon it. That’s why I was careful to say “_If you think about it…_” By entering into the argument, I’m forcing you to use conventional logic. Ain’t I a stinker? If you think about it, 2 + 2 = 4, no? It’s true because we agreed upon it when we defined arithmetic, same as fictional Billy’s fictional age being seven. What’s the external world got to do with it? (I also have, separately from this, stuff to say about the external world, which I’ll write it up later. But I want to make it clear that my argument that you know 2 + 2 = 4 to the same extent that you know you exist is independent of whatever I may say later on about “the external world”.) ---
**Author:** ![Beware\_of\_Doug](https://avatars.discourse-cdn.com/v4/letter/b/278dde/32.png) [@Beware\_of\_Doug](https://boards.straightdope.com/u/Beware_of_Doug)\ **Post date:** [April 6, 2009, 6:09pm UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/38 "2009-04-06T18:09:14Z")
> [@Rigamarole](#): > > Your premise is called [solipsism](http://en.wikipedia.org/wiki/Solipsism), the idea that “I alone exist”, and it has been around since at least the time of Gorgias, who lived from 483 to 375 B.C. I am not a solipsist, in that I believe that other people really do exist and have at least some level of consciousness. I do, however, believe something similar, which is that: a) No one can be conscious enough of what _I_ am feeling or thinking to truly relate to me as an individual. b) The same is true of a small but significant minority of people. c) Such people are not necessarily superior or inferior in any intrinsic way; they’re just _different_. d) This may indeed explain much of what we call social or spectrum disorders. ---
**Author:** ![DagNation](https://avatars.discourse-cdn.com/v4/letter/d/ee7513/32.png) [@DagNation](https://boards.straightdope.com/u/DagNation)\ **Post date:** [April 7, 2009, 12:51am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/39 "2009-04-07T00:51:58Z")
The “Matrix” or “aliens have our brains in a jar” idea has not been discussed much here. Is there different a name for that? This is different in that I am not inventing my whole world, but that the world I _think_ I live in is fictional and created by an outside force. There are a few ways to go with this one: 1. There is only me and a really good computer generating everything and everybody else. 2. I and some other people really exist as brains somewhere, but most people are NPCs (shopkeepers, all the other drivers on the road, etc). 3. All people exist as wired up brains, but what we see in the mirror is an avatar, and all this face to face interaction is all happening in a virtual world. I agree that exploring this too far is a silly waste of time. If all that I experience is fictional then what is the point? It is worth taking to the point of a high level of scepticism though. What I want to know, if we are in the “Matrix”, why don’t we have magic, FTL space ships, time traveling, etc?!? I would like to go visit a vulcan, or be an elf, or fly around magically… I’m sure it would be a simple programming upgrade… Another take on it is that the universe is the computer, and I am an instance of “earthling:human” that is “experiencing” life for whatever reason the computer/universe exists. It might be trying to form a question that makes the answer “42” have meaning. Fun diversion, but I am fairly sure that we are all here. Dag ---
**Author:** ![Kozmik](https://avatars.discourse-cdn.com/v4/letter/k/8dc957/32.png) [@Kozmik](https://boards.straightdope.com/u/Kozmik)\ **Post date:** [April 7, 2009, 1:08am UTC](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955/40 "2009-04-07T01:08:47Z")
> [@Gabba\_Gabba\_Hey](#): > > No, because I still don’t know that the external world is real. Dream Logic (i.e. conventional logic) says that that which performs an action must exist in at least some form. I don’t need access to the “real” world to prove it because it’s true by definition. If I say, imagine there’s a boy named Billy who is seven years old, you will never be able to disprove that Billy is seven. It’s true because we agreed upon it. That’s why I was careful to say “_If you think about it…_” By entering into the argument, I’m forcing you to use conventional logic. Ain’t I a stinker? Betrand Russell, in [Problems of Philosophy](http://www.ditext.com/russell/rus12.html), said something similar: > [@](#): > > The other objection to this definition of truth is that it assumes the meaning of ‘coherence’ known, whereas, in fact, **‘coherence’ presupposes the truth of the laws of logic.** [Previous page](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955.md?page=1) [Next page](https://boards.straightdope.com/t/do-you-only-know-that-you-exist/491955.md?page=3)