BS: Can you prove a negative?

Subject: BS: Can you prove a negative?
From: GUEST,Ed
Date: 12 Sep 03 - 05:14 PM

The United Nations has given Iran a deadline to prove that it isn't trying to develop nuclear weapons. (See this BBC story, for example).

This strikes me as being somewhat unfair.

If you accused me of being a paedophile, and challenged me to prove that I wasn't, I think I'd have great difficulty in findind 'proof' of my innocence. In fact, I don't see how I could.

An extreme example I know, but seriously, can you prove a negative?

Subject: RE: BS: Can you prove a negative?
From: TIA
Date: 12 Sep 03 - 05:26 PM

Nope. See here for people smarter than me explaining it in just this context. We just went through this with Iraq.

It's the NY Times - you'll have to sign in, but it costs nothing

Subject: RE: BS: Can you prove a negative?
From: GUEST,Martin Gibson
Date: 12 Sep 03 - 05:38 PM

OK, I accuse you of being a paedophile, and will consider you one until you can prove otherwise.

I had always heard that you might be a paedophile.

Life isn't always fair.

Subject: RE: BS: Can you prove a negative?
From: Amos
Date: 12 Sep 03 - 05:39 PM

It depends on the proposition and the system about which it is made. The reason is that the absolute "not-ness" of a condition must be tested against all possible configurations of space and time where the test condition might exist.

I can prove that my house is not painted yellow at a particular point in time, but not that it will never be. I cannot prove that I am not dirty-minded. For a large system such as a nation, a negative proposition pretty well leads to an unbounded set of test cases (infinite proving required to be conclusive). In general a negative requirement involves a huge number of possible conditions in which "the system under consideration is NOT doing X" that it becomes practically impossible. It is much, much easier to prove something conclusively if it is framed as a positive statement.



A

Subject: RE: BS: Can you prove a negative?
From: McGrath of Harlow
Date: 12 Sep 03 - 05:42 PM

Maybe a firm promise that the USA and the UK will not invade Iran might be a good way of encouraging Iran to confirm that it had abandoned any plans to acquire nuclear weapons. Except who would expect anyone to believe a promise like that?

And when does Israel get required to get rid of the hundreds of nuclear weapons it is said to have stockpiled? (To say nothing of the Big Boys, notably the USA - but of course that is totally different. After all it is inconceivable that the USA could ever use nuclear weapons, especially against cities...)

Subject: RE: BS: Can you prove a negative?
From: Bobert
Date: 12 Sep 03 - 07:20 PM

Here we go again....

Georgie Porgie Blair gave Saddam the same puzzle to solve...

Now me and Wes Ginny slide rule have been workin' on this fir the last year and still ain't got squat fir an answer...

Bobert

Subject: RE: BS: Can you prove a negative?
From: Bill D
Date: 12 Sep 03 - 07:48 PM

well, we proved Iraq didn't have big booooomy weapons here, nor there..nor over there, either....not even under here.....but we were sure they had thought about it once, so we can never be sure they don't, huh? *shaking my head*   I guess we'd better go invade Iran next! You know all them folks think alike over there!

North Korea?, who brags about having nukes, and rattles them 3 times a week? Oh, we'll speak firmly to THEM! China? We won't even speak harshly to them...where would we get cheap shoes?

I have a funny feeling that we'd BETTER change administrations next year...

Subject: RE: BS: Can you prove a negative?
From: McGrath of Harlow
Date: 12 Sep 03 - 08:10 PM

Regime change in Washington, please!

Subject: RE: BS: Can you prove a negative?
From: LadyJean
Date: 12 Sep 03 - 11:27 PM

If Descartes idea, "I think therefore I am" is true, then George W. Bush does not exist.


(He doesn't think, therefore he isn't?)

Subject: RE: BS: Can you prove a negative?
From: Bill D
Date: 12 Sep 03 - 11:36 PM

no, sadly...flawed thinking still allows existance.
What we need him to be saying 14 months from now is "Gee, I thought I had it all figured out, but I guess you CAN'T fool all the people all the time"

Subject: RE: BS: Can you prove a negative?
From: mousethief
Date: 13 Sep 03 - 12:16 AM

what Bill D said.

Subject: RE: BS: Can you prove a negative?
From: GUEST,sorefingers
Date: 13 Sep 03 - 02:39 AM

The answer is you can't but most people cannot comprehend they are being abused in that way.

The logical answer is always since 'Mr X is a Y' where he isn't and never was, is simply false so the question presupposes the conclusion, therefore the answer 'it is false that Mr X ... and this question is LOADED etc' disposes of the assumption.

Subject: RE: BS: Can you prove a negative?
From: gnomad
Date: 13 Sep 03 - 08:49 AM

I'm sure you cannot prove a negative (but I cannot prove it).

Subject: RE: BS: Can you prove a negative?
From: Amos
Date: 13 Sep 03 - 01:20 PM

Here's one that requires little proving: The Bush Presidency has not been good for this country...


A

Subject: RE: BS: Can you prove a negative?
From: Little Hawk
Date: 13 Sep 03 - 06:24 PM

I don't think it would be too hard to prove that George Bush and Tony Blair are not always honest. Just consult the record.

The powers that be are merely seeking a handy excuse to enlarge their existing overseas empire and move into Iran. And...they are seeking through a series of calculated news stories to gradually influence the American public and the British public into supporting such a move.

Iran is no real danger to Britain or America. Britain and America are a mortal danger to Iran. Same old story. The British have done this before in the Middle East, but the USA is a relative newcomer. They have, in fact, taken over from the defunct British Empire, and are playing the same old game under a new flag. The British are going along for the ride...it's better than having no empire at all. You might say that Britain is now to the USA what Greece was to Rome in Caesar's time.

- LH

Subject: RE: BS: Can you prove a negative?
From: McGrath of Harlow
Date: 13 Sep 03 - 06:58 PM

Actually I think Blair's idea might be that people will look at the Americans and the British in Iraq, and get impressed that the British troops are better at this stuff than the Americans. Not that good, but better.

Basically two reasons for that - long practice in doing this kind of thing on the ground, and the kind of professionalism you expect from mercenaries.

Subject: RE: BS: Can you prove a negative?
From: GUEST,Nick
Date: 13 Sep 03 - 10:34 PM

Would it not be twice as hard to prove a double negetive?

Subject: RE: BS: Can you prove a negative?
From: gnu
Date: 14 Sep 03 - 05:07 AM

No.

Subject: RE: BS: Can you prove a negative?
From: GUEST,Wolfgang
Date: 14 Sep 03 - 09:52 AM

Of course you can. Each time you prove that an integer is a prime number you prove a negative.
The way this question more recently has been discussed is in terms of whether the search space is finite or not.
Amos has posted a wonderful example in which the search space is finite at this moment in time but infinite when you consider all future moments in time. The obvious solution is to think of an example in which the search space is also finite if you look at all future times. Prime numbers are just one such example. There are many more such examples in mathematics.

Wolfgang

Subject: RE: BS: Can you prove a negative?
From: GUEST,Wolfgang
Date: 14 Sep 03 - 10:48 AM

Tony Pasquarello (1984): "There dawns a sneaking suspicion that the impossibility of proving a negative might be one of the universally accepted platitudes that unfortunately just happens to be false."

One of my first homework assignements in my first university course in mathematics was to prove that there is no largest prime number. The response 'You can't prove a negative' wouldn't have been rewarded with any point.

Wolfgang

Subject: RE: BS: Can you prove a negative?
From: Peter T.
Date: 14 Sep 03 - 11:20 AM

McGrath is right on this one. If the United States pledged under no circumstances to invade Iran and confronted Israel over its nuclear weapons program, something might come of it. The invasion of Iraq proved to everyone that the only real preventative to American invasion is nuclear weapons. That is one reason why I opposed it: no one with any sense believed Irag had nuclear weapons, and the other weapons it might have had were trivial, part of the stupid carelessness in the use of the phrase "weapons of mass destruction" (the thing that killed Dr. Kelly was this stupid phrase). It was bound to escalate the demand for nuclear weapons. The Pakistanis and the North Koreans are on record as taking this lesson to heart. Part of one's despair at the American administration is this terrible, terrible stupidity that will drive us into a new escalation race.

yours,

Peter T.

Subject: RE: BS: Can you prove a negative?
From: Amos
Date: 14 Sep 03 - 11:22 AM

It is perfectly possible to prove some negatives, as WG has pointed out -- as I said further up it depends on the nature of the proposition being "proved". But in general, in engineering circles, the principle is to form requirements in positive terms to make testable propositions out of them.

A

Subject: RE: BS: Can you prove a negative?
From: Amos
Date: 14 Sep 03 - 01:16 PM

Wolfgang:

Can you describe the approach you took in plain language?

A

Subject: RE: BS: Can you prove a negative?
From: McGrath of Harlow
Date: 14 Sep 03 - 04:02 PM

As Wolfgang pointed out, if the search space is limited and searchable, proving a negative is quite possible. You can prove there is no tiger in the living room without much difficulty. Proving there is no tiger in the whole country is a lot harder, but in principle possible, because it would at least in theory be poossoble to conduct a thorough search. Proving that there never was a tiger in the country is impossible, because in principle you cannot search the past.

In legal situations the presumption of innocence until proved guilty applies. Until recently it was recognised that to require people to prove their innocence of a charge was a clear indication of the exitence of an essentially tyrannical and opppressive regime.

Myself, I'd say that that is still the case, and I very much regret the lurch in that direction by a number of regimes which, however imperfect, used to draw the line at that kind of thing.

Subject: RE: BS: Can you prove a negative?
From: GUEST,Wolfgang
Date: 14 Sep 03 - 04:52 PM

Amos, I'm not completely sure what you mean with your question but if it is what I think you mean the proof goes roughly like that:

Imagine there is a largest prime number (idea: start with an assumption and if you can show that this assumption leads to a contradiction the assumption must be wrong). Then the number of prime numbers must be finite. You multiply all of them and add one. The resulting number is not dividable by any of the prime numbers on you list, therefore it must be a new prime number which contradicts your assumption.

Wolfgang

Subject: RE: BS: Can you prove a negative?
From: McGrath of Harlow
Date: 14 Sep 03 - 05:22 PM

Of course numnbers as such don't exist in the sense that tigers do.

Subject: RE: BS: Can you prove a negative?
From: Don Firth
Date: 15 Sep 03 - 02:30 PM

It may be different in mathematics, but—

On the original question:—    No. Demanding that one prove a negative is on the formal list of logical fallacies. The matter has been argued since Aristotle's time, and it always comes out the same. It's called the Fallacy of the Appeal to Ignorance (Proving a Negative). The rule is "an argument that asserts a claim is true because no one can prove it is untrue attempts to shift the burden of proof from the claimant to the opponent."

The way this works is I say, "What do you mean, I'm fishing through the bowl of mixed nuts and picking out all the cashews? I'm not the one who's doing it. There's an invisible gremlin (or tiger, if you insist) in this room, and he's doing it." You say, "That's crazy! There's no such thing as an invisible gremlin." I say, "Oh, yeah? Prove there isn't!"

Unfair. And illogical. Now, I could try to claim that your statement "There's no such thing as an invisible gremlin" is an assertion and that you have to prove it, but since I'm the one who brought up the gremlin in the first place, it falls to me to supply the proof. Basic freshman logic, Philosophy 115.

Our system of jurisprudence is based on this. You are innocent until proven guilty. If you are accused of a crime, it is the responsibility of the accuser to supply the proof. You are not required to prove your innocence.

Anyone who wants to engage in spirited discussion and not wind up throwing a lot of logical gutterballs ought to spend some time with this page:   http://chuma.cas.usf.edu/~pinsky/logicguide.htm. [I tried to put the URL in a link, but for some reason, Mudcat's "Preview" told me it was a "forbidden HTML tag" and woundn't display it, so you'll have to crank it by hand.] Good stuff, and fairly concise. Print it out. Keep it handy.

Don Firth

Subject: RE: BS: Can you prove a negative?
From: McGrath of Harlow
Date: 15 Sep 03 - 02:35 PM

That invisible gremlin has been messing with you, Don. It worked fine for me.Here

Subject: RE: BS: Can you prove a negative?
From: Don Firth
Date: 15 Sep 03 - 02:43 PM

Hmm. Strange. I just upgraded my computer and installed Windows XP, and even though it's reputed to be more stable, it's been doing some weird stuff lately. Maybe there is an invisible gremlin lurking near my CPU. But at this point, it's only a hypothetical gremlin. It's existence remains to be proven. Thanks for posting the link.

Don Firth

Subject: RE: BS: Can you prove a negative?
From: wysiwyg
Date: 15 Sep 03 - 02:50 PM

Can you prove a negative?

Can you prove you can't? :~)

~S~

Subject: RE: BS: Can you prove a negative?
From: Amos
Date: 15 Sep 03 - 03:20 PM

OR that you're not a weisenheimer?


A

Subject: RE: BS: Can you prove a negative?
From: Amos
Date: 15 Sep 03 - 03:56 PM

Don:


Appeal    to Ignorance (Proving a Negative): an argument that asserts a claim is true    because no one can prove it is wrong; this shifts the burden of proof to the    audience or opponent rather than the claimant

This is correctly listed as a form of fallacy. BUT it does not address the question of this thread which asks whether or not it is possible to prove a negative. The fal;;acy described here is demanding that one disprove an assertion when it should be the asserter's burden to prove it.

That's different/


A

Subject: RE: BS: Can you prove a negative?
From: Don Firth
Date: 15 Sep 03 - 05:21 PM

Granted, it is sometimes possible to prove a negative. But it is not logically required of the respondent.

As I pondered rummaging around in another country and trying to locate the egg on their faces, it occurs to me that this might be equivalent to the matter addressed in the Fourth Amendment to the U. S. Constitution: unreasonable search and seizure. Who's going to decide whether or not there is probable cause? The U. N. Security Council? Or George W. Bush and Company?

Oh, crap!!! Here we go again!

By the way, not to be a nasty old pinch-penny, but since the American taxpayer is having to buy the last round, who's going to pick up the tab for this one?

Don (heavy sigh) Firth

Subject: RE: BS: Can you prove a negative?
From: Mr Red
Date: 15 Sep 03 - 05:22 PM

NO

but you can negative a prove............

disprove.

Subject: RE: BS: Can you prove a negative?
From: McGrath of Harlow
Date: 15 Sep 03 - 05:44 PM

And you can disprove a negative readily enough, and prove a positive.

Same thing really. "There's no tiger in this room." But there was... And the tiger proved that by eating the man who doubted it's presence.

Subject: RE: BS: Can you prove a negative?
From: McGrath of Harlow
Date: 15 Sep 03 - 05:45 PM

And you can disprove a negative readily enough, and prove a positive.

Same thing really. "There's no tiger in this room." But there was... And the tiger proved that by eating the man who doubted its presence.

Subject: RE: BS: Can you prove a negative?
From: Amos
Date: 15 Sep 03 - 06:49 PM

Well, we hadn't gotten around to securing those rights for the people of Iraq yet, Don...since they haven't adopted a constitution, and they also insists on misapplying their right to bear arms.


A

Subject: RE: BS: Can you prove a negative?
From: Don Firth
Date: 15 Sep 03 - 07:06 PM

Hmm. . . . Got a point, I guess. (Another deep sigh).

Don Firth

Subject: RE: BS: Can you prove a negative?
From: The Fooles Troupe
Date: 16 Sep 03 - 03:02 AM

But best of to try to disprove something

remember the old dilemma

"Have you stopped beating your wife yet?"


:-)

Robin

Subject: RE: BS: Can you prove a negative?
From: GUEST,sorefingers
Date: 16 Sep 03 - 08:16 PM

Prove that in your kitchen you do not have the means to make meth?

Is another example

Subject: RE: BS: Can you prove a negative?
From: Mr Red
Date: 17 Sep 03 - 04:34 PM

My Kitchen is a total Meth. Except when I stop eating then it is just a Mess.