# Can't Prove a Negitive?

**URL:** <https://boards.straightdope.com/t/cant-prove-a-negitive/152654>\
**Category:** Great Debates\
**Created:** [February 4, 2003, 4:48am UTC](https://boards.straightdope.com/t/cant-prove-a-negitive/152654 "2003-02-04T04:48:38Z")\
**Posts on this page:** 7\
**Page:** 2

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**Author:** ![Liberal](https://avatars.discourse-cdn.com/v4/letter/l/848f3c/32.png) [@Liberal](https://boards.straightdope.com/u/Liberal)\
**Post date:** [February 4, 2003, 6:47pm UTC](https://boards.straightdope.com/t/cant-prove-a-negitive/152654/21 "2003-02-04T18:47:19Z")

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You can’t prove that I can’t prove that you can’t prove a negative. 😃

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**Author:** ![Iamthat](https://avatars.discourse-cdn.com/v4/letter/i/c6cbf5/32.png) [@Iamthat](https://boards.straightdope.com/u/Iamthat)\
**Post date:** [February 4, 2003, 6:57pm UTC](https://boards.straightdope.com/t/cant-prove-a-negitive/152654/22 "2003-02-04T18:57:32Z")

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\*\* ultrafilter\*\*

> [@](#):
>
> You can prove that something doesn’t exist by showing that its supposed properties are logically inconsistent.

You can’t prove my perceptions are consistent with yours.

You can’t prove what’s blue to you isn’t red to me.

(in another thread erislover said, The existence of a red rose in the dark has meaning but no existence, which I disagreed with.)

You can’t prove a red rose doesn’t exist in the dark?

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**Author:** ![Bippy\_the\_Beardless](https://avatars.discourse-cdn.com/v4/letter/b/ac8455/32.png) [@Bippy\_the\_Beardless](https://boards.straightdope.com/u/Bippy_the_Beardless)\
**Post date:** [February 4, 2003, 7:06pm UTC](https://boards.straightdope.com/t/cant-prove-a-negitive/152654/23 "2003-02-04T19:06:41Z")

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“You can’t prove a negative” is a short snappy and somewhat wrong way of saying  
“You can only prove something doesn’t exist, if you can define some attributes of the ‘something’ and can conduct an exhaustive search”  
.

So you can prove that the Loch Ness Monster does not exist, because the loch ness monster has attributes we can search for (size = big) and a limited area in which it can be found (Loch Ness) but it would require you to drain the Loch Ness through a sufficiently fine filter. We would then find all objects within Loch Ness of size greater than the filter size, and if we find no monsters in the filter we can say Loch Ness Monster != exist…

Of couse the work involved is far tto great to be practical, so instead the converse of proving that Loch Ness Monster does exist, and assuming it doesn’t exist until proof is forthcoming is more attractive.

On the other hand proving god does not exist is impossible since the parameters placed on gods existance are too fuzzy to allow an exhaustive search (maybe he is riding on a Neutreno somewhere near Alpha Centuri.  
Cheers, Bippy

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**Author:** ![Liberal](https://avatars.discourse-cdn.com/v4/letter/l/848f3c/32.png) [@Liberal](https://boards.straightdope.com/u/Liberal)\
**Post date:** [February 4, 2003, 7:08pm UTC](https://boards.straightdope.com/t/cant-prove-a-negitive/152654/24 "2003-02-04T19:08:06Z")

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That depends on who does the placing, I reckon.

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**Author:** ![Apos](https://avatars.discourse-cdn.com/v4/letter/a/838e76/32.png) [@Apos](https://boards.straightdope.com/u/Apos)\
**Post date:** [February 4, 2003, 7:30pm UTC](https://boards.straightdope.com/t/cant-prove-a-negitive/152654/25 "2003-02-04T19:30:50Z")

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Perhaps people should replace the thoughtless “you can’t prove a negative” with “How can WE distinguish your claim of X existing from it not existing?”

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**Author:** ![Iamthat](https://avatars.discourse-cdn.com/v4/letter/i/c6cbf5/32.png) [@Iamthat](https://boards.straightdope.com/u/Iamthat)\
**Post date:** [February 4, 2003, 8:14pm UTC](https://boards.straightdope.com/t/cant-prove-a-negitive/152654/26 "2003-02-04T20:14:57Z")

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X exists.

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**Author:** ![Liberal](https://avatars.discourse-cdn.com/v4/letter/l/848f3c/32.png) [@Liberal](https://boards.straightdope.com/u/Liberal)\
**Post date:** [February 4, 2003, 8:24pm UTC](https://boards.straightdope.com/t/cant-prove-a-negitive/152654/27 "2003-02-04T20:24:35Z")

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> [@](#):
>
> \*Originally posted by Apos \*  
> \*\*Perhaps people should replace the thoughtless “you can’t prove a negative” with “How can WE distinguish your claim of X existing from it not existing?” \*\*

That’s an excellent suggestion!

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