I mean, he challenged me to prove that my mother existed, without seeing her. Obviously I couldn't.
You didn't have a phone number you could reach her with? You didn't have any memories of her? These are all sufficient evidence for her existence. And sufficient evidence is what we call "proof".
At the very least, you could tell him "I bet you a thousand dollars that I will later see my mother, when I go home" If he doesn't accept the bet, that's evidence he himself believes in the existence of your mother, as he expects to lose your bet.
His words babbling about "existence" mean nothing -- as his arguments connects to neither the present and the evidence you have now (your memories of your mother), nor the anticipated future. It's just babbling nonsense.
And sufficient evidence is what we call "proof".
Sorry, my nitpick alarm went off at this. I think it makes more sense to say, "You don't need infinite certainty, just sufficiently strong evidence, and in any case there will never be enough evidence for you to be 100% sure of anything."
Thank you (and others who have posted) for helping me with this silly argument.
:) I'll let you know how things turn out. He's quite clever at thinking on the spot.
Update:
I confronted him with many of these arguments.
He still expects that people will exist in the future.
I think I've figured it out. This is what is wrong with his belief.
Even if he's right, and people stop existing when we stop percieving them, it still won't change how we behave, or what we're expecting to happen. He expects to see his friends later, he just says he can't prove they exist at the moment. (I asked him about memories, he said that we still have memories of dead people, are they alive?)
When I think about it, it's like the tree dropping in the forest analogy. We're not anticipating different experiences. We both expect to see our mothers later. And we can both agree that we cannot percieve people when they aren't in front of us.
He's just choosing a rather complicated way to state the obvious. At least this is what I'm getting.
Am I right, guys?
There is a sense of "prove" which implies certainty. If your friend is using this sense he is right- you cannot be certain that people stop existing when you stop perceiving them. In fact, he is not being nearly skeptical enough. You can't be certain people people exist when you're perceiving them either! Your senses could be lying to you- in fact people often dream or hallucinate people who aren't really there.
But what we're doing when we say something exists is making a model to explain our sense perceptions. There are models consistent with our senses that do not involve people existing-- but they are bad models. Believing that all of reality is structured around your perception and that things come into and out of existence based on whether or not you sense them is not a very good model of the world. In fact it is a backwards and totally unhelpful model of the world. The point in saying "My mother exists" is to explain why you have all these sense perceptions: her image, the sound of her voice, memories of her, etc. The best way to explain and predict these perceptions is by thinking of your mother as an independently existing entity... "I saw my mother at 5:00 because that is when she gets home from work I didn't see her before then because she was at work." (note, one feature of hallucinations is that they usually don't lend themselves to being modeled as externally existing entities). And this isn't just true of people: it is true of all your beliefs.
Yes you are right, these are flaws in his argument.
I have trouble even expressing his position coherently. Is he really saying that objects in the universe blink out of existence when you are not perceiving them? If that is the case, how is state in those objects (such as the thoughts in your friend's head) maintained when they do not exist?
Maybe its as if there is a meta-universe with some notion of working memory that stores the objects while they are not existing. Of course this is very question begging, isn't the storage itself what we mean by existence?
Also the objects state isn't simply maintained, it advances in ways that are logically consistent with what you know about the object. Like your friend has maybe read another chapter of the book before you see him again. So its as if we have to have computation over this set of working memory, to work out what would be happening in them to keep them consistent with your model of reality. I personally would call this computation "existence" so it might be be advantageous if your friend goes down this track.
At this point he may well acknowledge that objects exist in some sort of separate or parallel universe when outside your perceptions. If you can trick him into taking this position you'll have him dead to rights.
That's probably the right answer. Still:
"Your see your nose in your peripheral vision whenever you have your eyes open. Does this perception cease to exist when you stop noticing it?"
You could also ask him what he would expect to happen if he were to close his eyes (or turn around), and you were to smack him on the head. Sure, you hitting him would be real in your "existence", but would he expect not to feel pain in his? That kinda goes along with floating beliefs vs. testable hypotheses; it is at least something to work with. And then, you could make it even more solipsistic by asking what happens if you both close your eyes before you smack him!
There is also the possibility of getting to understand what he thinks about other forms of sensation. You could bring up echolocation, blind people, using magnetic fields to sense, IR vision (can the soldier see you if they are looking at your heat signature through a building in pitch black? Would either of you exist in one another's world?)... the list can be long, but it all boils down to there being evidence that you existed that whole time. If you can reach out and touch someone; with hands, or with phones, or with innernets. If they can upload images on facebook, even when they left your country, and you can see pictures of them. Then you are not being honest of your meaning of 'existence' when you say "they don't exist to me".
Taboo "exists". Does the physical world contain things you don't see? Also, lack of absolute certainty doesn't imply confidence in absence, one shouldn't demand unavailable kind of proof and take its absence as evidence.
What Nesov and ArisKatsaris said.
Also, there's no crisp line saying images on the retina can constitute "proof" but memories cannot. Both are indirect evidence, the difference is in degree not in kind. Especially if you know yourself to have poor eyesight but reliable memory.
Your friend is an amateur. I don't have proof that people exist even when I can observe them directly in front of me.
(I do have really really really strong evidence, though. And when they leave and I'm left with mere really really strong evidence, that's still good enough for me too.)
How does his belief pay rent (http://lesswrong.com/lw/i3/making_beliefs_pay_rent_in_anticipated_experiences/)? Try to figure out how his predictions about the world differ from yours. If they don't, his extra belief isn't paying any rent; if they do, then you'll have an obvious test to see who's correct.
How could you come into contact with them again if you were in different universes? If your universe constantly communicates with theirs in order to know when to combine (when you begin to occupy adjacent corresponding space), in what sense do you occupy 'different universes'? How do you know there isn't just a wall that appears whenever you can't measure it - and how do you know it's there if you can't by definition measure it? (Note: only ask him these questions if you want to get back at him for confusing you.)
Also The Simple Truth, that one's good too.
Edit: I'm pretty sure the relevant bit is
Inspector Darwin looks at the two arguers, both apparently unwilling to give up their positions. “Listen,” Darwin says, more kindly now, “I have a simple notion for resolving your dispute. You say,” says Darwin, pointing to Mark, “that people’s beliefs alter their personal realities. And you fervently believe,” his finger swivels to point at Autrey, “that Mark’s beliefs can’t alter reality. So let Mark believe really hard that he can fly, and then step off a cliff. Mark shall see himself fly away like a bird, and Autrey shall see him plummet down and go splat, and you shall both be happy.”
We all pause, considering this.
“It sounds reasonable…” Mark says finally.
“There’s a cliff right there,” observes Inspector Darwin.
Autrey is wearing a look of intense concentration. Finally he shouts: “Wait! If that were true, we would all have long since departed into our own private universes, in which case the other people here are only figments of your imagination – there’s no point in trying to prove anything to us -”
A long dwindling scream comes from the nearby cliff, followed by a dull and lonely splat. Inspector Darwin flips his clipboard to the page that shows the current gene pool and pencils in a slightly lower frequency for Mark’s alleles.
(Emphasis mine.)
The presence of memories in your mind is evidence about things you can no longer see. When someone leaves your presence, you are left with a memory of them having existed. This should be very convincing evidence to you; it is quite rare to have clear memories of people that don't exist. On the other hand, if you try to communicate this evidence to other people, it's less convincing to them, because you might miscommunicate, or lie, and these are much more common than false memories.
Of course, it is possible that the person you remember having existed, stepped into an incinerator or otherwise stopped existing while you weren't looking. But focusing on sufficiently-rare exceptions is a mistake; you can't ever have 100-point-0 certainty about anything (that would require a literally-infinite amount of evidence), but 99-and-some-more-nines percent certainty really is sufficient. Emphasizing the difference between these two levels of certainty is usually an instance of the fallacy of gray.
As for the "personal worlds" stuff - we do in fact all occupy the same world, and talking about peoples' individual worlds is just a confused way of talking about the contents of different peoples' heads.
Others have linked some relevant articles, but I think the one that most directly addresses your question is Belief in the Implied Invisible. (I tried to expand it in the context of Tree Falls in a Forest ...)
Long story short, in order to have a model that says the person stops existing when unobserved, you immensely complicate your description of the world, because you would have to throw out all kinds of regularities you rely on, like conservation of mass.
You can certainly get away with simply positing the concept of "my reality" like your friend does, and say someone stops existing in that sense, but it's unclear what would be the point of doing so, since the concept is (as far as I can tell) precisely identical to "I don't detect that person", so you already have an expression for it.
Is your friend, by any chance, an infant?
Actually, I just thought of a definitive experiment that rules out this hypothesis. It's called Peek-a-Boo.
I think The Simple Truth, from the Map and Territory sequence has the answer to your question. It addresses this exact argument, in fact.
Oh, ok. In that case, I'll try to break the problem down a bit. What does "separate universes" mean, exactly? Your friend seems to be saying that people leave "your universe" when you can't see them, but in what sense are they actually leaving your plane of existence? Also, what is different about "your" universe versus someone else's? And how is it that two or more universes can "communicate" and overlap when the people in them can see each other? And does it have to be eyesight? What about talking to someone on the phone?
For these reasons and many others that I neglected to list, I don't think the idea that everyone occupies their own universe is at all coherent. It's grammatically correct, but the concept just doesn't make sense.
Adding to that, I think the concepts are identical in all their meaning and implications, leaving there to be no actual difference that can be made.
If what the friend says is true, there's also no reason why the presence of the mother is proof of her existence, for we could easily entertain solipsism.
Whoever thumbed up my comment about not understanding.... Why?
XD If someone doesn't understand something, I'm not going to slap them on the back and tell them "Good job."
It is not because you don't understand. It's because you took action based on that understanding that was useful. It both got you more explanation due to Tetronian's willingness to explain and also provided some evidence about how obvious the concept is for people in general.
I don't just vote on stuff as a way to reward social or intellectual impressiveness.
I mean, he challenged me to prove that my mother existed, without seeing her. Obviously I couldn't.
Beliefs pay rent in anticipated experience. Your belief that your mother exists means that you would expect to see her if you went to wherever she lives or whatever. So he wants proof? Bring him to her. Can't be done in class though.
Of course he might well have meant something entirely different by "exist" than I assumed above, but the ordinary interpretation of "my mother exists" (when she's not in the speaker's presence) is something like, "I have a model in my head saying that we'll see my mother if we go to [location]".
If he means something else though, then you'll simply have to ask what that something else is.
There is no flaw in his argument. He's given to a very aggressive skepticism.
The question I would pose is what grounds would you havefor adhering to the conjecture posed. If you accept his argument, what about your behavior should change? Can we derive any knowledge from his conjecture? If "no" and "nothing", then it's a valid question why we should believe it. If he persists, point to David Lewis and linguistic assent (outlined, wuite entertainingly, in "Elusive Knowledge"): that he can consider your view and his completely equivalent insofar as either of you have knkwkedge of any kind,.
Also, excuse my drunkenness.
Also, excuse my drunkenness.
I thought you were just making typos. This is surprisingly clear for the writings of someone inebriated.
I mean, he challenged me to prove that my mother existed, without seeing her. Obviously I couldn't.
You could, if you have sufficient sharp ears. Or smell sense. The point is, if you accept current physical law, even if your mother is space-like separated from you, there'll come a time when your future cones will interact, and in that case, provided you have sufficient sharp instruments, you could prove her existence. You could even entangle your matter with her, thereby reaching non-locality (or creating another universe, if you prefer realism). The only way to physically separate yourself from your mother is to make her cross an event horizon (cosmological or otherwise): in that case, no more physical interaction can occur and she will be gone for good.
Otherwise, as others have noted, the only way left is solipsism.
Celia Green writes:
Since old-fashioned philosophy has been to so large an extent forgotten, perhaps I may summarise its principal findings, which were all related to what we may call the principle of total uncertainty. It is impossible to be sure that what we are looking at is really there, impossible to be sure that our apparent memory of even the most recent event is not a delusion, impossible to be certain that the object we leave in a room is identically the same when we return and not merely a precise reproduction of the one we left, and impossible to be sure that anything is ever causally related to anything else, no matter how many times they are perceived in close conjunction.
This principle of uncertainty gave rise to a famous philosophical dilemma, known as the Problem of Knowledge. The problem in question was to distinguish some kind of knowledge or of mental activity to which the principle of uncertainty did not apply. A considerable amount of thought was expended over a long period on attempts, frequently convoluted and never entirely conclusive, to delineate such an area of knowledge. This might have led people to suspect that there was in fact no such area...
This is the actual situation. In my opinion, appearances do provide a form of knowledge, but only a very superficial sort: So long as the appearance is there, you know it is there. And even then, when you reflect on an appearance, some possibility of error reenters the situation. (Husserl's long analyses of certainty and uncertainty in phenomenology may be the most insightful thing ever written on this topic.)
The comments elsewhere on this page ask you to think in terms of probability. But what justifies these probabilities? The argument for persistence of objects is that, so far in your life, they are usually still there when you look for them again; also, that the data about the world is consistent with the hypothesis that objects do persist and that it contains many other people who have experienced this. But if you examine your experiences logically, all that you really know is that so far, you have had a series of experiences consistent with this interpretation. You do not know that these appearances - of objects and of people - correspond to persistent realities with an existence independent of your perceptions, nor do you know that your experience will continue to be consistent with this hypothesis.
Nor do you know that this hypothesis is the most probable interpretation of your experience, because you don't actually know the set of all possible worlds and the conditions under which your life-experience typically occurs to a possible being. It could be that your experience is actually most characteristic of a certain type of dream experienced by 29-dimensional hyperfnords, and that across the whole multiverse it is only rarely that such experiences are veridical (that they are literally true). In that case, the rational interpretation of events would be to say that the objects and people of your experience aren't real, they don't exist when not attended to, they are just a product of your dreaming mind and you could wake up at any moment.
The comments elsewhere on this page ask you to think in terms of probability. But what justifies these probabilities? [...] But if you examine your experiences logically, all that you really know is that so far, you have had a series of experiences consistent with this interpretation. {emphasis mine}
'really know' also signifies a probability. What makes p=1 so much more important than p=.99999?
It could be that your experience is actually most characteristic of a certain type of dream experienced by 29-dimensional hyperfnords,
Everything is connected. My mother provided my existence in the first place. When she walks out of the room, she still breathes in oxygen and breathes out carbon dioxide, she still consumes food and water, releases methane, sheds skin as dust, absorbs sunlight, and consumes products. This book I hold in my hand, it required the existence of a bookbinder, of a writer, of an editor, an accountant, a tax man, a delivery man, a construction worker, a copyright official, and on and on. These people poured their existence into that object, just as all of my ancestors going back a billion years poured their existence into me. Right now, me typing this on a screen, requires all of them, everything, all connected, all pouring into this moment. Without those people, without those worlds and physical laws, without even you, without your questions and thoughts, I wouldn't be here, doing this; I would be someone else, or nothing at all.
I am, therefore you are.
He does not understand the difference between map and territory. He thinks that he thinks that existence in the territory depends on existence in his map.
Oh, ok. In that case, I'll try to break the problem down a bit. What does "separate universes" mean, exactly? Your friend seems to be saying that people leave "your universe" when you can't see them, but in what sense are they actually leaving your plane of existence? Also, what is different about "your" universe versus someone else's? And how is it that two or more universes can "communicate" and overlap when the people in them can see each other? And does it have to be eyesight? What about talking to someone on the phone?
For these reasons and many others that I neglected to list, I don't think the idea that everyone occupies their own universe is at all coherent. It's grammatically correct, but the concept just doesn't make sense.
Adding to that, I think the concepts are identical in all their meaning and implications, leaving there to be no actual difference that can be made.
If what the friend says is true, there's also no reason why the presence of the mother is proof of her existence, for we could easily entertain solipsism.
So I have a friend who I sit next to in class, and we talk about philosophy. Well today, he brought up that when people leave your presense, and you can't observe them any longer, you no longer have proof they exist.
Well I pointed out that it would violate the conservation of mass law, right?
So then, with a bit more prodding, I figured out that by "no longer exist", he means they exist in their world, but they no longer exist in mine. So basically you can't prove that anyone exists unless they're directly in front of you.
I'm really not certain how to go about answering this question. I mean, he challenged me to prove that my mother existed, without seeing her. Obviously I couldn't.
Is he right? Or is there some flaw in his argument, some fallacy that I'm missing?
I went through a few of the Sequences, and the closest article I could find was about not believing in the invisible. But in this case, he doesn't literally (I think) believe they just vanish, he believes they enter alternate universes that are selected when I come in contact them again.
My mind is boggled. I also apologize if this is dumb question, and it's common knowledge or has already been answered, and to my credit, I did make an attempt to figure out the answer before bothering you all. Thanks.