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gnosis
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 Posted: Thu Sep 18, 2008 8:35 pm Post subject: Is this logically correct? |
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(Posted from another forum):
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Originally posted by AKA_gnosis
No, I am asserting that something has not been shown conclusively to exist, and therefore must be assumed not to exist until evidence shows otherwise.
As Alvin Plantinga has pointed out, the unqualified principle that you are endorsing here – the principle that any positive existential claim must be assumed false unless there is conclusive evidence to the contrary is going to commit you to contradictions.
Let’s accept for the sake of argument that there is no conclusive evidence that God exists. Let’s also accept for the sake of argument that there is no conclusive evidence that God does not exist.
From your principle it follows that we must assume
(1) God does not exist.
But now consider the following positive existential claim: There is a human being who was not created by God. That’s also a positive existential claim. So your principle commits us to assuming that it’s false. So your principle commits us to the following:
(2) It is not the case that there is a human being who was not created by God.
Now (2) is logically equivalent to
(3) All human beings were created by God.
Now, for a certain technical reason, we need to add the following to generate a contradiction (but it’s an unobjectionable premise):
(4) There are human beings.
Now the conjunction of (3) and (4) entails
(5) There is a human being that was created by God.
But (5) obviously entails
(6) God exists
So your principle commits us to making assumptions that entail both (1) and (6). But (1) and (6) are contradictory. So by reductio ad absurdum, your principle is false.
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(Sorry reposted in the correct section)
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Eyedunno
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| Posted: Thu Sep 18, 2008 8:44 pm Post subject: |
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GODDAMMIT! Whoever moved this thread made me lose my reply.  What, am I supposed to copy everything I type in any new thread or thread that's full of trolls? Shit.
ANYWAY,
Assuming that "any positive existential claim must be assumed false unless there is conclusive evidence to the contrary", yeah, it sounds right to me.
However, we can't assume it true without evidence either, and the burden of proof seems to be on this person, so the ball is in his or her court.
Also, remember that fantastic claims require fantastic evidence. As Hume put it, a miracle (being something that contradicts the bulk of our day-to-day experiences) may be reasonably discounted unless any possibility of its being false is even more miraculous.
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WashMDJD
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| Posted: Thu Sep 18, 2008 9:21 pm Post subject: Re: Is this logically correct? |
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| gnosis wrote: | (Posted from another forum):
| Quote: |
Originally posted by AKA_gnosis
No, I am asserting that something has not been shown conclusively to exist, and therefore must be assumed not to exist until evidence shows otherwise.
As Alvin Plantinga has pointed out, the unqualified principle that you are endorsing here – the principle that any positive existential claim must be assumed false unless there is conclusive evidence to the contrary is going to commit you to contradictions.
Let’s accept for the sake of argument that there is no conclusive evidence that God exists. Let’s also accept for the sake of argument that there is no conclusive evidence that God does not exist.
From your principle it follows that we must assume
(1) God does not exist.
But now consider the following positive existential claim: There is a human being who was not created by God. That’s also a positive existential claim. So your principle commits us to assuming that it’s false. So your principle commits us to the following:
(2) It is not the case that there is a human being who was not created by God.
Now (2) is logically equivalent to
(3) All human beings were created by God.
Now, for a certain technical reason, we need to add the following to generate a contradiction (but it’s an unobjectionable premise):
(4) There are human beings.
Now the conjunction of (3) and (4) entails
(5) There is a human being that was created by God.
But (5) obviously entails
(6) God exists
So your principle commits us to making assumptions that entail both (1) and (6). But (1) and (6) are contradictory. So by reductio ad absurdum, your principle is false.
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(Sorry reposted in the correct section) |
My response would be that the claim identified by the person making this argument "There is a human being who was not created by God" is misidentified as a positive existential claim. I think, rather, that is is actually two claims conjoined. The claims are "It is the case that this human being exists" and "It is not the case that this being was created by God." The first claim is a positive existential claim. The person making the claim that the entity in question exists should be required to show cause to believe it to be so, or else have his claim dismissed. The second claim is a negative existential claim - and is the default position until evidence can be shown for the truth of that claim. In other words, the sentence is two claims - one is an existential claim about the person and the other is an existential claim about a characteristic of that person.
Evidence will be required to show the existence of the person, but no evidence will be required to show the nonexistence of some trait of the person (like not being created by God). We need no additional proof to believe that Terrence exists beyond seeing him. We need no evidence to believe that Johnny did not have a daydream about playing basketball later this afternoon. The absence of a trait is a negative existential question for which no evidence is needed.
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Intellecta prius quam sint, contempta reliquas."
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("...that my gifts here set forth for you with faithful solicitude, may not by you be contempuously discarded before they have been understood.")
"Mes amis, si j'avance, suivez-moi! Si je recule, tuez-moi! Si je meurs, vengez-moi!" --Henri de la Rochejaquelein |
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gnosis
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| Posted: Thu Sep 18, 2008 10:07 pm Post subject: |
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Thanks Wash.
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Eyedunno
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| Posted: Thu Sep 18, 2008 10:14 pm Post subject: |
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For the record, I still think the problem is with "something has not been shown conclusively to exist, and therefore must be assumed not to exist until evidence shows otherwise", and my prediction involves the theist, pwnage, gnosis, and the theist not being on the receiving end of said pwnage. 
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gnosis
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| Posted: Thu Sep 18, 2008 10:25 pm Post subject: |
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| Eyedunno wrote: | | For the record, I still think the problem is with "something has not been shown conclusively to exist, and therefore must be assumed not to exist until evidence shows otherwise", and my prediction involves the theist, pwnage, gnosis, and the theist not being on the receiving end of said pwnage. |
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Eyedunno
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WashMDJD
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| Posted: Thu Sep 18, 2008 10:47 pm Post subject: |
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I agree, but I'm not sure that's the way that Gnosis meant the statement that is being labeld as an argument from ignorance. I didn't read Gnosis as suggesting that "If no evidence for the truth of a positive existential proposition has been given, then the proposition is false" is a rule of logic. I read Gnosis as suggesting that it was a rule of practical reasoning.
Ultimately, in the absence of evidence, we must retreat to the position of agnosticism (if it seems that evidence could never be provided, even in theory) or to simply saying that the truth content of the claim is unknown. But as a practical matter, that answer does one a not a whit of good. We rightfully look on the fellow who claims that grasshoppers mentally beam telepathic messages of love into his brain with a bit of worry, even though no evidence is forthcoming about the truth of his positive existential claim. Can we prove his claim false? No. Can he prove his claim true? No. But that doesn't stop even the most skeptical amongst us from coming to the firm conviction that the fellow probably needs some medication.
EDIT: I didn't notice earlier, but I think you probably meant that point as well, Eyedunno, since the website you linked to contained the same information - sorry. D'oh!
| Eyedunno's linked website wrote: |
IV. Non-fallacious uses of the ad ignorantiam: in science, the law courts, and some specific other situations, one must, for practical reasons, assume that something is false unless it is proved true and vice-versa. |
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"Ne mea dona tibi studio disposta fideli,
Intellecta prius quam sint, contempta reliquas."
-Lucretius, De rerum natura
("...that my gifts here set forth for you with faithful solicitude, may not by you be contempuously discarded before they have been understood.")
"Mes amis, si j'avance, suivez-moi! Si je recule, tuez-moi! Si je meurs, vengez-moi!" --Henri de la Rochejaquelein |
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gnosis
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| Posted: Thu Sep 18, 2008 10:53 pm Post subject: |
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Thanks for the link Eye, interesting stuff. I don't know much about logic but I have been trying to educate myself more.
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Eyedunno
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| Posted: Thu Sep 18, 2008 11:24 pm Post subject: |
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Yeah, I was under the impression that they were strictly arguing logic.
But from a practical perspective, things are more complicated. If I say there's a street in front of my friend's house (I didn't say my house, cuz I pasted that picture of a fallen tree a few days ago  ), it's not reasonable to assume that that statement is false. Even though you don't have evidence that it's true, you probably won't assume it's false or suspend judgement on it, since odds are the majority of houses you've seen have streets in front of them, and thus you will probably assume I'm telling the truth, and I would hold that you are being reasonable in doing so.
I like to use this example (statements numbered for convenience):
1) I bought a car yesterday.
2) The car is orange.
3) The car is a Ferrari.
4) The car can fly.
5) Only I can see the car.
In fact, none of these statements are true, but in most circumstances (assuming I'm not known as a pathological liar or something) most people would not suspend belief on statement #1. Orange cars are somewhat rare, but still not completely out of the ordinary, so statement #2 would probably pass without much controversy.
When we get to statement #3, most people will start to doubt it. Ferraris are expensive, produced in low numbers (a few thousand per year), and prospective buyers often wait years to get one. By statement #4, you can be pretty sure I'm bullshitting you, cuz, I mean, a flying car? It may not be impossible, but I don't think any have been produced, least of all by Ferrari.
And finally, statement #5 sounds like an excuse for me not providing evidence. That doesn't mean it is just an excuse, but given how unbelievable the stuff above it is, you're pretty safe discounting it as such, and discounting my flying Ferrari along with it.
So I once again point to Hume (specifically "Of Miracles" from An Enquiry Concerning Human Understanding).
Edit: Here it is.
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