#### Pete Svarrior

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##### Re: Is it possible to prove a negative?
« Reply #40 on: December 28, 2013, 07:19:46 PM »
Assuming there is no evidence is not an assumption of falsehood.  It is assuming that it is true that there is not evidence.
Correct, but also irrelevant.

If we are not speculating then we must assume

#### Rama Set

##### Re: Is it possible to prove a negative?
« Reply #41 on: December 28, 2013, 08:25:32 PM »
Assuming there is no evidence is not an assumption of falsehood.  It is assuming that it is true that there is not evidence.
Correct, but also irrelevant.

It is relevant, because saying, "I have looked and there is no evidence" is an assertion that in and of itself carries a BOP.

#### Pete Svarrior

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##### Re: Is it possible to prove a negative?
« Reply #42 on: December 28, 2013, 08:31:35 PM »
It is relevant, because saying, "I have looked and there is no evidence" is an assertion that in and of itself carries a BOP.
How is it relevant to the subject of "Is it possible to prove a negative?"?

If we are not speculating then we must assume

#### Rama Set

##### Re: Is it possible to prove a negative?
« Reply #43 on: December 28, 2013, 08:41:18 PM »
It is relevant, because saying, "I have looked and there is no evidence" is an assertion that in and of itself carries a BOP.
How is it relevant to the subject of "Is it possible to prove a negative?"?

This thread was started because Tom said, "I have looked and there is no evidence for the controls in this gravity experiment.  Prove me wrong." (more or less).  He claimed he was being critical of a the contention that there is evidence for the controls in this experiment, but he was not being critical, he was asserting the negative viewpoint.  This thread was essentially to determine whether or not Tom had a burden of proof.

#### markjo

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##### Re: Is it possible to prove a negative?
« Reply #44 on: December 28, 2013, 11:08:43 PM »
Assertions of any and all sorts deal with things that are true (or presumed to be true), not things that are false.
I assert that your premise is false.
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Science is what happens when preconception meets verification.

Ignorance more frequently begets confidence than does knowledge. -- Charles Darwin

If you can't demonstrate it, then you shouldn't believe it.

#### Pete Svarrior

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##### Re: Is it possible to prove a negative?
« Reply #45 on: December 28, 2013, 11:27:24 PM »
Feel free to. It won't make you any less wrong.

If we are not speculating then we must assume

#### markjo

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##### Re: Is it possible to prove a negative?
« Reply #46 on: December 28, 2013, 11:49:04 PM »
Feel free to. It won't make you any less wrong.
And attacking a straw man won't make you right.
Abandon hope all ye who press enter here.

Science is what happens when preconception meets verification.

Ignorance more frequently begets confidence than does knowledge. -- Charles Darwin

If you can't demonstrate it, then you shouldn't believe it.

#### Pete Svarrior

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##### Re: Is it possible to prove a negative?
« Reply #47 on: December 28, 2013, 11:54:08 PM »
And attacking a straw man won't make you right.
You're right, I shouldn't waste my time attacking your straw man. Now, if you'd like to add something to this discussion, feel free to, but otherwise, please stop attempting to derail this thread.

If we are not speculating then we must assume

#### markjo

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##### Re: Is it possible to prove a negative?
« Reply #48 on: December 29, 2013, 12:50:03 AM »
And attacking a straw man won't make you right.
You're right, I shouldn't waste my time attacking your straw man. Now, if you'd like to add something to this discussion, feel free to, but otherwise, please stop attempting to derail this thread.
I'm sorry if you are unable to understand that it is possible to assert a negative claim and therefore incur a burden to support that negative claim.
Abandon hope all ye who press enter here.

Science is what happens when preconception meets verification.

Ignorance more frequently begets confidence than does knowledge. -- Charles Darwin

If you can't demonstrate it, then you shouldn't believe it.

#### Pete Svarrior

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##### Re: Is it possible to prove a negative?
« Reply #49 on: December 29, 2013, 12:47:06 PM »
I'm sorry if you are unable to understand that it is possible to assert a negative claim and therefore incur a burden to support that negative claim.
Yes, it's difficult to understand how you could use a word to mean its opposite without committing an error of some sort. So far, you have not succeeded.

If we are not speculating then we must assume

#### Rama Set

##### Re: Is it possible to prove a negative?
« Reply #50 on: December 29, 2013, 01:48:23 PM »
I'm sorry if you are unable to understand that it is possible to assert a negative claim and therefore incur a burden to support that negative claim.
Yes, it's difficult to understand how you could use a word to mean its opposite without committing an error of some sort. So far, you have not succeeded.

No one is doing that.

#### Pete Svarrior

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##### Re: Is it possible to prove a negative?
« Reply #51 on: December 29, 2013, 03:16:21 PM »
No one is doing that.
Markjo is, by trying to "assert a negative". Again, assertions deal with truths, not falsities. I've already presented evidence to that fact, so unless you'd like to counter it with something credible, I'm going to consider this settled.

If we are not speculating then we must assume

#### bj1234

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##### Re: Is it possible to prove a negative?
« Reply #52 on: December 29, 2013, 03:50:02 PM »

Proving a negative

When the assertion to prove is a negative claim, the burden takes the form of a negative proof, proof of impossibility, or mere evidence of absence. If this negative assertion is in response to a claim made by another party in a debate, asserting the falsehood of the positive claim shifts the burden of proof from the party making the first claim to the one asserting its falsehood, as the agnostic position that "I don't believe that X is true" is different to the explicit denial "I believe that X is false".[8]

So please take a look at the bolded section.
This is exactly what has happened in the other thread.

I believe that I have already shown that negative assertions exist.  Something that seems to have been overlooked.

You also seem to be missing definition #3 on your page too

3  To maintain or defend, as a cause or a claim, by words or measures; to vindicate a claim or title to; as, to assert our rights and liberties.

This does not say anything about the claim being a positive or negative claim.  Just a claim.
« Last Edit: December 29, 2013, 03:52:26 PM by bj1234 »

#### markjo

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##### Re: Is it possible to prove a negative?
« Reply #53 on: December 29, 2013, 05:03:51 PM »
No one is doing that.
Markjo is, by trying to "assert a negative". Again, assertions deal with truths, not falsities. I've already presented evidence to that fact, so unless you'd like to counter it with something credible, I'm going to consider this settled.
I think that you are confusing the concepts of positive/negative and true/false.  They are not the same.
Abandon hope all ye who press enter here.

Science is what happens when preconception meets verification.

Ignorance more frequently begets confidence than does knowledge. -- Charles Darwin

If you can't demonstrate it, then you shouldn't believe it.

#### Pete Svarrior

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##### Re: Is it possible to prove a negative?
« Reply #54 on: December 29, 2013, 05:38:52 PM »
I think that you are confusing the concepts of positive/negative and true/false.  They are not the same.
If you ignore context, sure. If you don't, well...

If we are not speculating then we must assume

#### garygreen

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##### Re: Is it possible to prove a negative?
« Reply #55 on: December 29, 2013, 05:41:08 PM »
Again, assertions deal with truths, not falsities.

I might be misunderstanding what you've been saying in this thread.  To the extent that, for instance, 'Not P' means 'P is false,' we can assert falsities.  This is true for many logical systems (but not all), and it's definitely true of propositional logic.  I dunno anything about programming languages, so I'm out of my depth there; but, I take you to be saying that one cannot assert 'Not P' (or something to that effect) as a premise in propositional logic.

Is that an accurate interpretation?
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#### Pete Svarrior

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##### Re: Is it possible to prove a negative?
« Reply #56 on: December 29, 2013, 05:53:37 PM »
I might be misunderstanding what you've been saying in this thread.  To the extent that, for instance, 'Not P' means 'P is false,' we can assert falsities.  This is true for many logical systems (but not all), and it's definitely true of propositional logic.  I dunno anything about programming languages, so I'm out of my depth there; but, I take you to be saying that one cannot assert 'Not P' (or something to that effect) as a premise in propositional logic.

Is that an accurate interpretation?
That is accurate both for propositional logic and programming, but they still deal with positive claims in one way or another. You positively state something that is provable - ¬P falls into that category. However, in non-mathematical arguments, it is fairly easy to prove ∃ (you show that something exists, bam, done), and essentially impossible to prove ¬∃, because you'd then have to somehow exhaust the domain of the debate (which is often impossible to even define, and even more often simply inaccessible to the parties discussing). It is exactly because of the vagueness and inaccessibility of the domain that this sort of logic falls short. Can you prove that there exist no handkerchiefs in my pockets? You can't, and it would be unfair for me to request that. You can't access my pockets, you don't even know if I'm wearing clothes right now, so you can't possibly exhaust the domain of "all the things in my pockets".

Yes, it sometimes is possible to prove a negative, usually by proving another claim that implies said negative (e.g. if I can prove that my name is Frank, that implies that my name is not John, or, in propositional logic, any invocation of modus tollens), but it is often impossible when no such implication can be made. As people have already pointed out in this thread, absence of evidence is not evidence of absence, so if I do not provide you with any information about the contents of my pockets, my handkerchief hypothesis is unfalsifiable. Of course, that causes problems of its own, but you certainly can't disprove it.
« Last Edit: December 29, 2013, 05:57:40 PM by pizaaplanet »

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#### garygreen

• 3211
##### Re: Is it possible to prove a negative?
« Reply #57 on: December 29, 2013, 08:10:07 PM »
That is accurate both for propositional logic and programming, but they still deal with positive claims in one way or another. You positively state something that is provable - ¬P falls into that category.

I agree in the sense that the validity of a proof relies on the relationship between true premises.  In that regard we're always talking about true assertions and not false ones.  But the premises may contain negations, and negations are logically equivalent to 'false' in propositional logic.

Maybe I'm still misunderstanding you, but I'm saying that 'Not P' and 'P is false' are logically equivalent.  One can assert that P is false by asserting 'Not P' with no problems.  It seems like you're saying that one cannot assert that something is false in propositional logic.

I think this 'negative/positive' label is what's causing the confusion.  I dunno what it means to positively or negatively state something, and I think that the distinction is entirely superfluous.  Assertions are assertions.  They may contain negations.

However, in non-mathematical arguments, it is fairly easy to prove ∃ (you show that something exists, bam, done), and essentially impossible to prove ¬∃, because you'd then have to somehow exhaust the domain of the debate (which is often impossible to even define, and even more often simply inaccessible to the parties discussing). It is exactly because of the vagueness and inaccessibility of the domain that this sort of logic falls short. Can you prove that there exist no handkerchiefs in my pockets? You can't, and it would be unfair for me to request that. You can't access my pockets, you don't even know if I'm wearing clothes right now, so you can't possibly exhaust the domain of "all the things in my pockets".

If the domain is truly inaccessible or inexhaustible, then I agree with you.  But that's a question of soundness, not validity.  I totally agree that there is much room for debate about the truth of the premises in any of these discussions.  But those debates can be resolved, and those domains can be restricted.

That I personally cannot verify the contents of your pocket does not mean that it's impossible to prove that it contains no handkerchiefs.

P1.  If PP's pocket contains a kerchief, then I will find a kerchief when I reach my hand into PP's pocket.
P2.  I find no kerchief when I reach my hand into PP's pocket.
C: PP's pocket does not contain a kerchief.

I agree that I cannot resolve the truth of the premises from my current location, and we could probably debate/modify them to make them more accurate/specific/whatever.  But the truth value of the conclusion is logically provable.

Yes, it sometimes is possible to prove a negative, usually by proving another claim that implies said negative (e.g. if I can prove that my name is Frank, that implies that my name is not John, or, in propositional logic, any invocation of modus tollens), but it is often impossible when no such implication can be made. As people have already pointed out in this thread, absence of evidence is not evidence of absence, so if I do not provide you with any information about the contents of my pockets, my handkerchief hypothesis is unfalsifiable. Of course, that causes problems of its own, but you certainly can't disprove it.

Same as above, basically.  It might be difficult or impossible to resolve the truth of a particular premise, but that doesn't make the conclusion unprovable.  It's often simply a matter of modifying a premise or formulating the proof in a different way.
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#### Pete Svarrior

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##### Re: Is it possible to prove a negative?
« Reply #58 on: December 29, 2013, 09:09:42 PM »
Ah. If that's the perspective you want to take, then yes, pretty much everything is logically (dis)provable. I interpreted the topic to have a more practical aim.