Can one prove a being doesn't exist?

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Can one prove a being doesn't exist?

Postby webgrunt » Fri Nov 14, 2014 12:58 pm UTC

I'm not sure, but it seems to me that you can't prove a being doesn't exist.

Someone argued that you can, and said "for example, a male human who isn't male doesn't exist."

To me, this seems like semantics. I can see where this argument would work in math, but for an object or being, it's like saying "something that doesn't exist doesn't exist, therefore I've proven that something doesn't exist." You haven't proved something doesn't exist, you've defined something that doesn't exist. Is that the same as proof? In math maybe, but for objects or beings, it doesn't seem to make sense.

But I'm pretty sure I'm missing something. Can anyone help me understand this better?

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Re: Can one prove a being doesn't exist?

Postby PeteP » Fri Nov 14, 2014 2:15 pm UTC

You are right, if the definition isn't self contradictory you can't prove it doesn't exist. You can show that something doesn't exist at a specific place (if it's something which existence would be noticeable with existing sensory equipment) but we can hardly run an exhaustive search of the universe.
If you take laws of physics as a given, you can also show that something wouldn't work as described if physical laws hold (say a magma eating creature which is made of burnable material). Though technically they aren't proven either, they just fit extensive observations so that isn't really a proof.
Aside from that you can just argue why something is unlikely or that we have no reason to think it exists.

Well I suppose you could define a being to be so gigantic that we would notice it's existence. A galaxy sized being which glowed brightly in everchanging colors would be hard to miss, except that it could just be outside of the observable galaxy.
Or say the Megakraken at the Center of our galaxy. It's countless arms touch every sun in our galaxy to leech from their energy. Define the arms in a way that we would notice them.
But in that case I have defined where it is and defining something to be somewhere obserable and then showing it isn't there works in most cases.

Anyway proving a negative is often impossible, which is why we usually expect positive proof of somethings existence.

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Re: Can one prove a being doesn't exist?

Postby TheGrammarBolshevik » Sun Nov 16, 2014 8:23 am UTC

This is more a question of epistemology than a logic problem, and it might belong better in the "Serious Business" forum.

That being said, there are a few distinctions worth making here.

First, we need to know what, exactly is meant by "proof." In one sense, a proof is a deduction from certain assumptions that are considered rock-solid. Almost by definition, "proofs" in this sense are only found in mathematics - an assumption on any other subject isn't deemed "rock-solid" in the right kind of way to figure in a proof.

"Proof" is also used to refer to a conclusive demonstration, but one which might (a) not be deductive and (b) might depend on assumptions that are not "rock-solid" in the sense of the previous paragraph. For example, we might say "Holmes proved that Moriarty is the murderer" even though it's metaphysically possible that Moriarty isn't the murderer, even given the evidence. ("Metaphysically possible" means, roughly, "Might be possible if the laws of physics were different." So a perpetual motion machine is presumably metaphysically possible, while a male human who isn't male is presumably metaphysically impossible.)

Second, we need to know what kinds of "being" you have in mind. You draw a distinction between "objects or beings" on the one hand and things that we talk about in math on the other. I'm not sure it's right to exclude mathematical entities (e.g. numbers, sets) from the realm of objects and beings, but I think we can set that aside. I think what you might be getting at is the distinction between concrete objects and abstract objects. How to draw this line isn't precisely clear. One way of characterizing concrete objects is that they are either mental or physical (or both) - so I am a concrete object (mental and physical), a rock is a concrete object (physical), and God, if there were such a thing, would be a concrete object (mental). Another way of characterizing concrete objects is that they're the sort of thing that can play a role in causation. The examples I just gave work this same on this characterization: I am concrete (I can throw a rock), a rock is concrete (same), and God is concrete (since God can do anything that's metaphysically possible). And numbers, most people think, would be abstract objects.

Now, in the first sense of "proof," I think it's right to say that you can't prove that a concrete object can't exist. PeteP has already given much of the reason for this: You can't run an exhaustive search of the universe (let alone of whatever realm solely mental beings like God might reside in), and things like the laws of physics aren't "rock-solid" in the way that the first sense of "proof" requires. Indeed, as I mentioned above, the first sense more or less rules out any proof about anything that isn't mathematical, so our hopes of proving the non-existence of concrete objects are sunk.

However, it's worth pointing out that most of these reasons (apart from the "exhaustive search" one, which isn't really limited to the first sense of "proof") don't have anything special to do with proving that a being doesn't exist. That is, it would be equally difficult, by this standard, to prove that a concrete being does exist. For example, it's very clear that I have hands. But this is clear because of things like my sense experiences, and my sense experiences aren't "rock solid" in the way that's supposed to be involved in mathematical proof - I dream all kinds of nonsensical things all the time, after all. Don't get me wrong: I think there are very good reasons for believing that I have hands. But those reasons aren't a "proof," in the first sense.

In the second sense of "proof," I think there are lots of examples where we can prove that something doesn't exist. For example, we can prove that there is no Prime Minister of the United States by consulting authoritative resources on how the United States is governed. Or, following PeteP's example, we can prove that there's no magma-eating creature made out of paper. Or, to continue a previous example, Holmes might prove that a death was an accident, and thus prove that there is no murderer.

One other thing: I'm not sure I buy that the mathematical examples, where we can use the first sense of "proof," are examples of, as you put it, "defin[ing] something that doesn't exist." There's an apparent sense in which I'm just playing a word game if I say something like "A male human who isn't male doesn't exist." But it's at least not obvious that the same thing is going on with, for example, the proof that a greatest prime number does not exist.
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Re: Can one prove a being doesn't exist?

Postby CorruptUser » Mon Nov 17, 2014 4:35 pm UTC

The Loch Ness monster can be proved not to exist. A behemoth of a creature would have a behemoth appetite. If there is not enough fish in Loch Ness to support the monster, it must not exist. Furthermore, the lake must support a BREEDING population, which at bare minimum would be a hundred of these supposed creatures. So yeah, sometimes we can prove a negative.

But what this sort of question is usually used for is 'can we prove god doesn't exist'. We can't disprove the supernatural. But we don't have to. If the supernatural exists it will provide its own evidence. If not, we don't say "it doesn't exist", we just say "we have no evidence it exists". If it doesn't provide evidence it's effectively the same as not having any affect on our universe. And the more fantastic (as in, a fantasy) the story the more concrete the proof must be.

In the classic example, Alice can tell Bob she went to see a movie, and Bob will likely believe her because movies exist. If he asks for proof, Alice could provide a ticket stub or some such. While not concrete proof, it's probable that she's telling the truth. If Alice says that on the way to the movie theatre she encountered a flying unicorn which traveled to Narnia to slay the Jaberwokkie, we'd think Alice was insane because none of those things exist. Even if Alice provided a video recording, it's more likely that the video was faked than Alice was telling the truth, so we dismiss her story as a joke. The more extraordinary the claim, the more extraordinary the evidence required.

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Re: Can one prove a being doesn't exist?

Postby stoppedcaring » Mon Nov 17, 2014 4:49 pm UTC

In one sense -- a very loose sense, but a legitimate sense nonetheless -- everything that can be conceived does exist, even things which are inherently self-contradictory like square circles and non-male cisgender males. Simply by virtue of their being discussed, the mental state associated with their definition exists, and therefore they "exist" in that very limited sense.

What we can say for sure is that such a thing as a square circle, despite existing in concept, is inconsistent with the observed properties of geometry. We can even say it is inconsistent with logic itself. This doesn't make it disappear as a mentally-defined concept, but it's this inconsistency that we're really after.

The concept of the Loch Ness Monster certainly exists, and its properties are variously defined in the minds of many believers. The concept, however, is inconsistent with the constraints of biology, ecology, and population. So we can say "there is no Monster in Loch Ness", not because we have proven that the Loch Ness Monster doesn't exist, but because we have shown beyond reasonable doubt that the concept is inconsistent with our observations.

So in order to effectively prove that something doesn't "exist" in the vernacular sense, we just have to show an inconsistency between that concept and something observable.

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Re: Can one prove a being doesn't exist?

Postby quantropy » Mon Nov 17, 2014 5:06 pm UTC

Immanuel Kant wrote:Existence is not a predicate

You get into trouble when you treat existence as a property of a 'thing' which it can either have or not have. To say 'X does not exist' means you have to be really really sure what you mean by X.

e.g. Santa Claus is a being who brings you presents at Christmas. Well you get presents, so obviously Santa Claus exists. No, Santa Claus lives at the North pole. So if a being who lived 2 miles from the North pole and brought everyone in the world presents, that wouldn't be Santa Claus? Or if an arctic explorer sends you presents, is that person Santa Claus? You just get into a neverending attempt to try to define what you mean by 'Santa Claus'

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Re: Can one prove a being doesn't exist?

Postby stoppedcaring » Mon Nov 17, 2014 7:40 pm UTC

quantropy wrote:
Immanuel Kant wrote:Existence is not a predicate

You get into trouble when you treat existence as a property of a 'thing' which it can either have or not have. To say 'X does not exist' means you have to be really really sure what you mean by X.

This very statement highlights what you're saying -- the "thing" is the existence of the concept itself. You can't define something without the definition existing.

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Re: Can one prove a being doesn't exist?

Postby TheGrammarBolshevik » Mon Nov 17, 2014 8:50 pm UTC

CorruptUser wrote:But what this sort of question is usually used for is 'can we prove god doesn't exist'. We can't disprove the supernatural. But we don't have to. If the supernatural exists it will provide its own evidence. If not, we don't say "it doesn't exist", we just say "we have no evidence it exists".

If you accept "If the supernatural exists it will provide its own evidence" and "The supernatural hasn't (and won't) provide its own evidence," then "It doesn't exist" follows by modus tollens. I don't know where this idea of reserving judgment comes from, especially since you haven't provided any sort of argument for it.

quantropy wrote:e.g. Santa Claus is a being who brings you presents at Christmas. Well you get presents, so obviously Santa Claus exists. No, Santa Claus lives at the North pole. So if a being who lived 2 miles from the North pole and brought everyone in the world presents, that wouldn't be Santa Claus? Or if an arctic explorer sends you presents, is that person Santa Claus? You just get into a neverending attempt to try to define what you mean by 'Santa Claus'

It seems to me that one should reject the idea that "Santa Claus" means the same thing as some description. That is, "Santa Claus exists" doesn't mean "A being who brings you presents exists," nor does it mean "A being near the North Pole who brings you presents exists," nor could any other modification of the description capture the meaning of "Santa Claus exists." (And note, by the way, that "A being who brings you presents" isn't even a definite description, so it's already a poor candidate to give the meaning of a name - what if there are two people who bring you presents?)

It is interesting, though, that Santa Claus comes up in Kripke's original causal theory of names. He notices something along the lines of: There was a real person named Saint Nicholas, and references to "Santa Claus" ultimately trace back to this person. But it still seems wrong to say things like "Santa Claus was a real person, who attended the Council of Nicaea." So perhaps "Santa Claus" is a tough example.

But I think there are lots of other examples that don't suffer from this weirdness. For example, there's nothing strange about saying "Jesus was a real person, but he was just an ordinary person who lived and died and stayed dead; no miracles or divinity or anything like that." So "Jesus" doesn't mean the same thing as the definite descriptions that Christians would associate with that name. And saying "Jesus didn't exist" is something different than saying that a definite description like "the Son of God" fails to refer.

quantropy wrote:
Immanuel Kant wrote:Existence is not a predicate

A minor historical note: Kant did not say that existence is not a predicate. He said that it is not "a real predicate, i.e., a concept of something that could add to the concept of a thing" (A598/B626). So the point is that, e.g., the concept of a dog is the same concept as the concept of an existing dog. This is a narrower point than to deny that there is a such a predicate as existence.

stoppedcaring wrote:This very statement highlights what you're saying -- the "thing" is the existence of the concept itself.

There's a prima facie distinction to be made between a thing and the concept of a thing. If you want to say that a thing can somehow be its own concept, you're probably going to have to say a lot more.
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Re: Can one prove a being doesn't exist?

Postby CorruptUser » Mon Nov 17, 2014 9:03 pm UTC

No, 'it doesn't exist' doesn't strictly follow. It's Russell's Teapot; we don't know there isn't a teapot out there in between the Earth and Mars, but we have absolutely no reason to suspect that there is one so either provide evidence or stop claiming you 'know' it's there. That's why Dawkins (or was it Hitchens?) claims he's a 6.9 on the Atheist Kinsey scale.

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Re: Can one prove a being doesn't exist?

Postby TheGrammarBolshevik » Mon Nov 17, 2014 9:17 pm UTC

Yes, it strictly follows by modus tollens from the premises that I indicated. This is a matter of basic deductive logic, and nothing that fucking Richard Dawkins says is going to change that.

Perhaps what's really going on is that you don't actually believe that "If the supernatural exists it will provide its own evidence." Or perhaps what's going on is that you have some very weird (albeit Internet-popular) ideas about what it takes to know something. For example, you say we don't know that there isn't a teapot between Earth and Mars. I say that anyone who thinks that is either seriously uninformed about astronomy, or has a contrived notion of what it is to know something.

But once you commit yourself to a strong premise like "If there are supernatural things, there is evidence for supernatural things," and another strong premise like "There isn't evidence for supernatural things," there isn't room for Dawkinsing around about what conclusions follow.
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Re: Can one prove a being doesn't exist?

Postby CorruptUser » Mon Nov 17, 2014 10:34 pm UTC

Prove to me you aren't a brain in a vat whose nerves are connected to some mad scientists' device, being fed a false reality.

You can't. That hypothesis is unfalsifiable. That doesn't mean it's necessarily wrong, just that it's absolutely useless as a theory because it predicts nothing.

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Re: Can one prove a being doesn't exist?

Postby TheGrammarBolshevik » Mon Nov 17, 2014 10:35 pm UTC

CorruptUser wrote:Prove to me you aren't a brain in a vat whose nerves are connected to some mad scientists' device, being fed a false reality.

Is there some reason you're asking me to do this?
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Re: Can one prove a being doesn't exist?

Postby CorruptUser » Mon Nov 17, 2014 10:41 pm UTC

Because I'm not the one claiming you can disprove the unfalsifiable.

Also your sig is wrong; orange rhymes with melange and phalange and of course Blorenge.
Last edited by CorruptUser on Mon Nov 17, 2014 10:45 pm UTC, edited 2 times in total.

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Re: Can one prove a being doesn't exist?

Postby TheGrammarBolshevik » Mon Nov 17, 2014 10:44 pm UTC

Neither am I. Perhaps you should look more carefully at what, exactly, I am claiming in the passages that you are objecting to.
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Re: Can one prove a being doesn't exist?

Postby The Great Hippo » Tue Nov 18, 2014 1:32 am UTC

CorruptUser wrote:Because I'm not the one claiming you can disprove the unfalsifiable.
'There's a teapot between Earth and Mars' is actually falsifiable, just not functionally so. After all, there's a limited space between Earth and Mars! Which means it is within the bounds of possibility to examine all of that space for the teapot. Also, I don't know much about logic, but I'm pretty sure that it does follow that if you 1) Presume the supernatural provides its own evidence, 2) Note there is no evidence of the supernatural provided, then this is sufficient evidence to disprove the supernatural.

To put it another way: Santa Claus visits every house on Christmas. Santa Claus didn't visit your house on Christmas. Either 1) Your initial statement was wrong, or 2) Santa Claus doesn't exist. If visiting every house on Christmas is part of Santa Claus' definition, then Santa Claus must not exist.

If providing evidence of itself is part of the definition of the supernatural -- and no such evidence exists -- then we can presume to know the supernatural doesn't exist.

(However, I see no reason to presume the supernatural must provide evidence of itself. That seems... very arbitrary.)
CorruptUser wrote:Also your sig is wrong; orange rhymes with melange and phalange and of course Blorenge.
The signature is wrong, but not for the reason you think: The claim is that the word 'nothing' rhymes with 'orange'.

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Re: Can one prove a being doesn't exist?

Postby CorruptUser » Tue Nov 18, 2014 2:06 am UTC

You can always move the goalposts into unfalsifiable territory. Just make the teapot progressively smaller until it's too small to even be detected at the subatomic level. Just declare that there is some sort of alien power cloaking the teapot, only detectable by stuff you haven't invented yet. It doesn't mean there are no invisible teapots being masked by aliens, only that it's effectively a nonsense claim to make with no evidence.

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Re: Can one prove a being doesn't exist?

Postby The Great Hippo » Tue Nov 18, 2014 2:31 am UTC

CorruptUser wrote:You can always move the goalposts into unfalsifiable territory. Just make the teapot progressively smaller until it's too small to even be detected at the subatomic level. Just declare that there is some sort of alien power cloaking the teapot, only detectable by stuff you haven't invented yet. It doesn't mean there are no invisible teapots being masked by aliens, only that it's effectively a nonsense claim to make with no evidence.
Right, but you weren't talking about subatomic teapots, or teapots being cloaked with alien technology. You were just talking about teapots in space. The claim 'There is a teapot somewhere between Earth and Mars' is falsifiable; the claim 'There is a teapot somewhere between Earth and Mars that cannot be detected by any of our instruments' is not.

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Re: Can one prove a being doesn't exist?

Postby Forest Goose » Tue Nov 18, 2014 6:42 am UTC

CorruptUser wrote:You can always move the goalposts into unfalsifiable territory. Just make the teapot progressively smaller until it's too small to even be detected at the subatomic level. Just declare that there is some sort of alien power cloaking the teapot, only detectable by stuff you haven't invented yet. It doesn't mean there are no invisible teapots being masked by aliens, only that it's effectively a nonsense claim to make with no evidence.


If you have to make a single fixed claim of that nature, it is still falsifiable unless you are claiming that it can never be detected. If I theoretically show that there should be a particle such that X, even if we can't detect at that scale now, we may be able to later - the Higgs is an example of that, as are countless others. So, if the claim is "There is a teapot cloaked by aliens" and the alien cloak can be presumed to be defeated at some point of technological sophistication, then it is falsifiable, we just can't carry out the experiment right now (we, realistically, couldn't search everywhere from here to mars for a teapot either, so being technically out of reach isn't an issue).

If you mean, instead, that the statement keeps shifting as evidence rules the current one out; then, yes, that is not falsifiable, but that's not a single statement either, that's being disingenuous. (that's not to say that a lot of people don't do this)
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Re: Can one prove a being doesn't exist?

Postby morriswalters » Tue Nov 18, 2014 12:56 pm UTC

The Great Hippo wrote:The signature is wrong, but not for the reason you think: The claim is that the word 'nothing' rhymes with 'orange'.
I am sad that the language I was taught turns out to be wrong. I was taught that Nothing and not even were somehow related through structure. Oh well back to school. Sigh.

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Re: Can one prove a being doesn't exist?

Postby Cres » Tue Nov 18, 2014 3:57 pm UTC

The deductive form of the Problem of Evil is a proof that God does not exist. Formal proof helpfully available here for those of a mathematical persuasion: http://plato.stanford.edu/entries/evil/validity.html

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Re: Can one prove a being doesn't exist?

Postby stoppedcaring » Tue Nov 18, 2014 4:14 pm UTC

The Great Hippo wrote:I'm pretty sure that it does follow that if you 1) Presume the supernatural provides its own evidence, 2) Note there is no evidence of the supernatural provided, then this is sufficient evidence to disprove the supernatural.

To put it another way: Santa Claus visits every house on Christmas. Santa Claus didn't visit your house on Christmas. Either 1) Your initial statement was wrong, or 2) Santa Claus doesn't exist. If visiting every house on Christmas is part of Santa Claus' definition, then Santa Claus must not exist.

If providing evidence of itself is part of the definition of the supernatural -- and no such evidence exists -- then we can presume to know the supernatural doesn't exist.

(However, I see no reason to presume the supernatural must provide evidence of itself. That seems... very arbitrary.)

And therein lies the rub.

However, this CAN be used to rule out specifically-defined conceptions of the supernatural. For example, studies showing that prayer has no effect on recovery rates of heart disease obviously doesn't rule out all god-concepts -- how could it? -- but it certainly rules out the concept of a God which can be reliably depended upon to aid the recovery of heart disease patients in response to specific prayer. Modern science does not rule out the existence of a creator, but it definitely rules out the existence of a (non-deceitful) creator who created the universe 6000 years ago and then killed everybody in a global flood 4000 years ago. And so forth.

If a definition is unfalsifiable, it is probably not a very good definition.

Cres wrote:The deductive form of the Problem of Evil is a proof that God does not exist. Formal proof helpfully available here for those of a mathematical persuasion: http://plato.stanford.edu/entries/evil/validity.html

This merely shows that a certain conception of God -- specifically, a God whose properties would compel him/her/it to prevent forms of suffering which persist -- cannot exist.

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Re: Can one prove a being doesn't exist?

Postby Cres » Tue Nov 18, 2014 4:24 pm UTC

stoppedcaring wrote:
Cres wrote:The deductive form of the Problem of Evil is a proof that God does not exist. Formal proof helpfully available here for those of a mathematical persuasion: http://plato.stanford.edu/entries/evil/validity.html

This merely shows that a certain conception of God -- specifically, a God whose properties would compel him/her/it to prevent forms of suffering which persist -- cannot exist.


Which, conveniently, is the conception of God endorsed by all major monotheistic religions, and all of their sophisticated apologists.

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Re: Can one prove a being doesn't exist?

Postby PeteP » Tue Nov 18, 2014 4:31 pm UTC

Cres wrote:The deductive form of the Problem of Evil is a proof that God does not exist. Formal proof helpfully available here for those of a mathematical persuasion: http://plato.stanford.edu/entries/evil/validity.html

Or rather that a god with narrowly defined properties doesn't exist.
However take omnibenevolence away from a being and I doubt people would stop calling a being God. Believers of an omnipotent god of course like ascribing it to their god: So show them an omnipotent being which created the world and sometimes interferes if it's in the mood but which is just kinda nice. Do you really think everybody who listed OB as a property of their god won't call it a god?.

The problem with a mathematical proof about the existence of supernatural beings based on the traits ascribed to it is that people don't tend give precise descriptions which have to be fulfilled exactly, even if sounds that way.
Take TGB applying modus tollens to CorruptUsers statements in this thread. It's Logically completly valid if CU intended it as an absolute necessary property of supernatural beings, but I doubt he did.
People tend to list common traits or traits they expect alongside things they consider essential to the definition. Some people might describe dragons as four legged. But if there is a giant, flying and fire breathing lizard which likes to collect treasures they probably will be willing to call it a dragon even if it only has two legs.

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Re: Can one prove a being doesn't exist?

Postby stoppedcaring » Tue Nov 18, 2014 4:38 pm UTC

Cres wrote:
stoppedcaring wrote:
Cres wrote:The deductive form of the Problem of Evil is a proof that God does not exist. Formal proof helpfully available here for those of a mathematical persuasion: http://plato.stanford.edu/entries/evil/validity.html

This merely shows that a certain conception of God -- specifically, a God whose properties would compel him/her/it to prevent forms of suffering which persist -- cannot exist.


Which, conveniently, is the conception of God endorsed by all major monotheistic religions, and all of their sophisticated apologists.

Eh, as Pete points out, that's not necessarily the case. The typical conception of God endorsed by mainstream evangelicalism, for example, is a being whose compulsion to an abstract sense of justice/mercy/master-plan (which is somehow both defined by God and yet not?) preempts the compulsion to prevent suffering.

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Re: Can one prove a being doesn't exist?

Postby Cres » Tue Nov 18, 2014 4:39 pm UTC

PeteP wrote:Or rather that a god with narrowly defined properties doesn't exist.


Not just "narrowly defined". Exactly defined. That's the point. My point is not about which definition of God you prefer, (although, again, if you read any academic philosophy of religion, the 3 omni definition is one most theists would endorse). My point is that you can prove that something (namely, 3-omni-God) does not exist, without relying on a definition that is internally inconsistent (3-omni-God would be consistent with a world where we had observed no instances of pointless suffering).

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Re: Can one prove a being doesn't exist?

Postby stoppedcaring » Tue Nov 18, 2014 5:29 pm UTC

But as Weinersmith points out, most people are not terribly bothered by a concept of God which sacrifices one or more of the omnis, so in practice the Problem of Evil disproves only an edifice.

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Re: Can one prove a being doesn't exist?

Postby TheGrammarBolshevik » Tue Nov 18, 2014 6:18 pm UTC

Cres wrote:The deductive form of the Problem of Evil is a proof that God does not exist. Formal proof helpfully available here for those of a mathematical persuasion: http://plato.stanford.edu/entries/evil/validity.html

Nb. This is, at best, a proof in the detective's sense, not in the mathematician's sense, since it relies on an empirical premise.
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Re: Can one prove a being doesn't exist?

Postby cphite » Tue Nov 18, 2014 10:32 pm UTC

CorruptUser wrote:The Loch Ness monster can be proved not to exist. A behemoth of a creature would have a behemoth appetite. If there is not enough fish in Loch Ness to support the monster, it must not exist. Furthermore, the lake must support a BREEDING population, which at bare minimum would be a hundred of these supposed creatures. So yeah, sometimes we can prove a negative.


The Loch Ness monster is supposedly (according to the most common speculation) somewhere around 2,500 lbs - which is big but less than half the mass of an average elephant. Loch Ness is 23 miles long, about a mile wide, and very deep; and filled with numerous large fish and even some mammals like seals, otters, etc. Plenty of room (and food) for a number of such creatures... We have no way of knowing how long the creature lives, or how often it multiplies - so setting a bare minimum population of one hundred is pure speculation.

But what this sort of question is usually used for is 'can we prove god doesn't exist'. We can't disprove the supernatural. But we don't have to. If the supernatural exists it will provide its own evidence. If not, we don't say "it doesn't exist", we just say "we have no evidence it exists". If it doesn't provide evidence it's effectively the same as not having any affect on our universe. And the more fantastic (as in, a fantasy) the story the more concrete the proof must be.


If the supernatural exists then it isn't subject to what we consider to be rules for our universe in the first place. So, god(s) could exist and assert whatever level of control he/she/they desire over us - ranging between no control and absolute control - without ever producing evidence that we humans can detect, or at least recognize.

In the classic example, Alice can tell Bob she went to see a movie, and Bob will likely believe her because movies exist. If he asks for proof, Alice could provide a ticket stub or some such. While not concrete proof, it's probable that she's telling the truth. If Alice says that on the way to the movie theatre she encountered a flying unicorn which traveled to Narnia to slay the Jaberwokkie, we'd think Alice was insane because none of those things exist. Even if Alice provided a video recording, it's more likely that the video was faked than Alice was telling the truth, so we dismiss her story as a joke. The more extraordinary the claim, the more extraordinary the evidence required.


Like claiming that the universe we think we see around us is real, rather than an elaborate simulation being run in some larger universe, despite the odds being strongly in favor of the latter.

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Re: Can one prove a being doesn't exist?

Postby stoppedcaring » Wed Nov 19, 2014 6:03 pm UTC

cphite wrote:The Loch Ness monster is supposedly (according to the most common speculation) somewhere around 2,500 lbs - which is big but less than half the mass of an average elephant. Loch Ness is 23 miles long, about a mile wide, and very deep; and filled with numerous large fish and even some mammals like seals, otters, etc. Plenty of room (and food) for a number of such creatures... We have no way of knowing how long the creature lives, or how often it multiplies - so setting a bare minimum population of one hundred is pure speculation.

If we define it more specifically, we can draw more specific conclusions. For example, if we restrict "Nessie" to a descendant of plesiosaurs, that allows us to place certain constraints on population, the likelihood of fossil evidence, and so forth. Similarly, if we say Nessie is a biological creature which is not the descendant of any other species on Earth, then we can make predictions about how "she" got here, which we can also test for consistency with observation.

If the supernatural exists then it isn't subject to what we consider to be rules for our universe in the first place. So, god(s) could exist and assert whatever level of control he/she/they desire over us - ranging between no control and absolute control - without ever producing evidence that we humans can detect, or at least recognize.

Yet another reason to define one's views of God/the divine/whatever based around specific claims, rather than abstract minimalist theism. It does very little good to speculate concerning supernaturalism simpliciter when there are so many distinctly-defined God-concepts to be evaluated.

Absolute-vs-relative epistemology comes into play here as well. Extraordinary claims require extraordinary evidence to be accepted as "true", but they require a somewhat lesser standard to be accepted as "useful", and an even lower standard to be accepted as "reasonably probable". It would take extraordinary evidence to prove beyond reasonable doubt that I am not a brain in a vat, but it is very useful to assume that I am not a brain in a vat.

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Re: Can one prove a being doesn't exist?

Postby Autolykos » Wed Nov 19, 2014 8:43 pm UTC

Absolute-vs-relative epistemology comes into play here as well. Extraordinary claims require extraordinary evidence to be accepted as "true", but they require a somewhat lesser standard to be accepted as "useful", and an even lower standard to be accepted as "reasonably probable".

This probably comes a lot closer to the actual level of belief found among (sane, adult) religious people. It's not a direct belief in the existence of god (even if they claim to do so), but more a belief in belief: "I think it is good to believe, therefor I want to believe, therefor I believe I believe."
Elizer says it way more eloquently than I can: http://lesswrong.com/lw/i4/belief_in_belief/

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Re: Can one prove a being doesn't exist?

Postby stoppedcaring » Wed Nov 19, 2014 10:16 pm UTC

Even though we talk about things as being "true", that's never strictly the case. Logic, the scientific method, and so on aren't "true" in the absolute fundamentalist-inerrancy definition; they're "true" in the sense of being consistently useful and predictive.

Autolykos wrote:It's not a direct belief in the existence of god (even if they claim to do so), but more a belief in belief: "I think it is good to believe, therefor I want to believe, therefor I believe I believe."

It's a spectrum.

"Do you believe Jesus rose from the dead?"

Some people will say "Yes, because the Bible said so, and it's good to trust the Bible completely." Some will say "Yes, because otherwise where did Christianity come from?" Some will say "Yes, but I don't know it for sure; it's just what I've chosen to base my worldview on." Some will say, "No, but I think it could have happened that way." Some will say, "No, and I'm sure there would be more evidence if it had happened." Some will say, "No, and I'm sure there would be more evidence of Jesus's existence if he had ever existed at all."

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Re: Can one prove a being doesn't exist?

Postby TheGrammarBolshevik » Wed Nov 19, 2014 10:47 pm UTC

I don't know what you mean by a "fundamentalist-inerrancy" definition of truth. Truth isn't ordinarily taken to imply that something is known with certainty, or even that it's known at all. For example, "Snow is white" is a true sentence. It's true because of the color of snow - not because I've looked at snow and seen what color it is. Or if I throw a coin into a dark room, either "The coin is heads up" or "The coin is tails up" or "The coin did not land on either face" is true - the truth of any such sentence doesn't require me to have any knowledge of how the coin landed.
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Re: Can one prove a being doesn't exist?

Postby stoppedcaring » Wed Nov 19, 2014 10:53 pm UTC

TheGrammarBolshevik wrote:I don't know what you mean by a "fundamentalist-inerrancy" definition of truth. Truth isn't ordinarily taken to imply that something is known with certainty, or even that it's known at all. For example, "Snow is white" is a true sentence. It's true because of the color of snow - not because I've looked at snow and seen what color it is. Or if I throw a coin into a dark room, either "The coin is heads up" or "The coin is tails up" or "The coin did not land on either face" is true - the truth of any such sentence doesn't require me to have any knowledge of how the coin landed.

Eh, the truth of all those statements -- statements which are true by definition -- depends on the truth of logical axioms, which ultimately are only taken to be true because they are useful and reliable but cannot ultimately be proven.

The "fundamentalist-inerrancy" definition of truth is the sort that would claim an ultimate source of propositional truth is necessary for any meaning to exist.

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Re: Can one prove a being doesn't exist?

Postby TheGrammarBolshevik » Wed Nov 19, 2014 11:07 pm UTC

No, none of those statements is "true by definition." This should be especially obvious in the case of the coin - how can it be "true by definition," as opposed to true by particular physical circumstance, that a coin falls in a given way? (But also in the other example: what definition of "snow" or "white" is there which, in itself, makes "Snow is white" true?)

Nor is there any obvious sense in which "The coin is face up" depends on the truth of logical axioms. Which logical axioms, exactly, make that sentence true? Further, what does this have to do with whether the sentence is true, regardless of what anyone knows about it, which is what I was talking about? You seem to think that if X can't be proved, and Y depends on the truth of X, then Y depends on proof in order to be true. But no such inference follows.

Nor is it at all clear that logical axioms are "taken to be true because they are useful and reliable."

I feel compelled to ask: What is your basis for saying any of this? Because you are speaking as if the things that you are saying are obvious truths that anyone acquainted with the subject would accept. When in fact the things you are saying are, across the board, either obviously false or extremely controversial among philosophers. It is, of course, acceptable to disagree with philosophical consensus. But it's to be expected that you give an argument when doing so, rather than presenting your views with the confidence of an expert.
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Re: Can one prove a being doesn't exist?

Postby Forest Goose » Thu Nov 20, 2014 4:37 am UTC

stoppedcaring wrote:Even though we talk about things as being "true", that's never strictly the case. Logic, the scientific method, and so on aren't "true" in the absolute fundamentalist-inerrancy definition; they're "true" in the sense of being consistently useful and predictive.


Logic and the Scientific Method are methods, the only way I can see to apply "true" to them is in the sense that they yield truths, everything else here seems to be about specific statements being true. At any rate, a major part of the basis for science is that it does not yield absolute truths; this is why experiments keep getting done and theories replaced, no one expects them to be true - in other words, you're not really pointing anything out that isn't immediate.

As for logic, I wholeheartedly disagree: deductive logic, by definition, moves from true statements to true statements. If you are divorcing truth from logic, then we are no longer speaking about the same truth. We can disagree on what rules are valid, but I don't believe we can disagree on Logic, in general, being verdical.

Of course it is possible to disagree with senses as an epistemic ground; so, perhaps "Snow is white" may be false, despite appearing white, because I cannot trust my senses to yield truths. I'm sure this could be argued to various degrees (and has been), but I'm not exactly sure how much bearing it has here unless something close to a skeptical position is being taken.
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Re: Can one prove a being doesn't exist?

Postby Reko » Sat Nov 22, 2014 4:23 pm UTC

Forest Goose wrote:so, perhaps "Snow is white" may be false, despite appearing white, because I cannot trust my senses to yield truths. I'm sure this could be argued to various degrees (and has been), but I'm not exactly sure how much bearing it has here unless something close to a skeptical position is being taken.


This was kind of what I was thinking when I first came across this thread. I find it easier to disprove things than it is to prove them because one instance of a falsehood can negate a whole lot of truth. For example, "all snow is white" may appear true at first, but you only need a single, non-white snowflake to prove this statement false.

So, for the OP, can you prove something doesn't exist? In all practical purposes, no you can't in my opinion. Because you would have to search or explore (or whatever) every possible instance that this being could exist and then come to a conclusion that way, and let's say that you could do this simultaneously so that you wouldn't miss anything, it is still possible that said being could exist in the future.

Does this mean that something MUST exist because you can't disprove it? No. While I can't DISprove there isn't an invisible cat in the chair next to me, based on my observations of the known world I feel confident that it is a fact that there is NOT an invisible cat on that chair.

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Re: Can one prove a being doesn't exist?

Postby phillip1882 » Mon Dec 15, 2014 9:48 pm UTC

i personally think you can prove some beings don't exist if that being's existence is self contradictory.
for example, i can't prove a horse with a spiral horn and wings doesn't exist, but i can prove that horse that's fire and ice at the same time doesn't exist. because fire and ice are opposites and such a thing would be contradictory.
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Re: Can one prove a being doesn't exist?

Postby elasto » Tue Dec 16, 2014 1:35 am UTC

phillip1882 wrote:i personally think you can prove some beings don't exist if that being's existence is self contradictory.
for example, i can't prove a horse with a spiral horn and wings doesn't exist, but i can prove that horse that's fire and ice at the same time doesn't exist. because fire and ice are opposites and such a thing would be contradictory.

Even that you can't really prove.

Imagine that our universe is actually a simulation, and there's a cube in front of the two of us which I interact with and experience as on fire and you simultaneously interact with and experience as as made of ice.

After we communicated with each other and could rule out other causes like one of us being mad or on drugs, we might conclude that the best way to describe the cube would be to say it was simultaneously fire and ice at the same time (as well as concluding our universe is actually a simulation...)

Since we can't prove that our universe is not a simulation we can't prove that the above couldn't occur.

(But we're deep into semantic and hair-splitting territory now...)

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Re: Can one prove a being doesn't exist?

Postby TheGrammarBolshevik » Tue Dec 16, 2014 4:12 am UTC

It's not clear to me that the fire/ice being is "contradictory." A paradigmatic example of a contradiction is "Such-and-such a thing is on fire and not on fire." It's contradictory because it both asserts and denies the very same thing. This is generally held to be impossible not merely as a matter of the laws of physics, but rather as a matter of the laws of logic (e.g., nothing could be both on fire and not on fire even if the laws were different). But it seems to me that, if it's even true that nothing can be both made of ice and on fire at the same time, it's true only contingently, as a matter of the laws of physics. There's no reason it couldn't be the case, say, that ice had a much higher melting point.
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Re: Can one prove a being doesn't exist?

Postby ucim » Tue Dec 16, 2014 4:28 am UTC

phillip1882 wrote:i can prove that horse that's fire and ice at the same time doesn't exist. because fire and ice are opposites and such a thing would be contradictory.
Sounds like you are pretty close to proving photons and electrons don't exist.

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