Proving a Negative

1. Double negatives
    Just as with someone who says, "I haven't done no crime!". Do they mean:

    a.  There is no crime that they haven't committed?
    b.  That they have done no crime? I.e. They have committed no crime.
    c.  That they haven't done a crime? I.e. They haven't committed a crime.
    d.  That they have done crime? I.e. What they have done, was a crime.

    So too with "You can't prove a negative". Do they mean (for example):

    a.  You can't prove that pigs can't fly. (Or even; You can't prove that flying pigs don't exist.)
    b.  You can prove that pigs can't fly.
    c.  You can't prove that pigs can fly.
    d.  You can prove that pigs can fly.

    In the first case (the suspected criminal), it's generally interpretations b or c, which the claimant means with their double negative.

    Claims b and c (in each example), mean the same thing, as do a and d.

    When people use a double negative, It is important to get them to clarify which of the three interpretations (b, c or d) do they mean. Double negatives are ambiguous.

2. Unfalsifiable
    If something is unprovable, then it is untestable and unscientific.

    When someone says, "You cannot prove ..." then they are warning me that what follows is probably unfalsifiable and unscientific.

    E.g. You can't prove that God exists. Or, you can't prove that God doesn't exist.

    Questions of religion or the supernatural are not scientific. Science is about the natural, the provable, the repeatable, the testable, the evidence.

3. Examples of provable negatives
    Here are five negative claims which are provable.
    I.e. You can prove that...:

        2 + 2 ≠ 5
        Sir Isaac Newton did not watch television.
        Kangaroos do not exist on the moon.
        I am not the smartest person in the world. (That should be self-evident)
        Automobiles did not exist in the 16th century.

    These are just a few exceptions to the "rule" that you can't prove a negative.

"The exception proves that the rule is wrong. That is the principle of science. If there is an exception to any rule, and if it can be proved by observation, that rule is wrong." – Richard Feynman, according to The Meaning of it All, 1999 ­­­

4. Can you prove that?
    The claim, "You can't prove a negative" is itself, a negative.

    Can you prove that you can't prove a negative?

    If you can, then you've contradicted your claim and the claim is false.
    If you can't, then the claim is meaningless and unfalsifiable.

    A negative claim which is not provable; "You cannot prove a negative".


5. "Universal, existential negative"
 If it is impossible to prove an existential universal negative then it is equally impossible to prove an existential universal affirmative. I.e. If it is impossible to prove that something does not exist somewhere in the universe, then it is equally impossible to prove that the same something does exist somewhere in the universe.

    For every negative claim which is impossible to prove then the opposite claim is also impossible to prove.
    If it is impossible to prove that pigs can't fly then it is impossible to prove that pigs can fly.
    If it is impossible to prove that God doesn't exist then it is impossible to prove that God does exist.

To highlight the lengths that some people will go to hold onto their "you can't prove a negative" myth, I came across this: (my bolding)

"You can't prove a negative" This Error is propagating across the internet, because of this article. People are beginning to say "ha you can prove SOME negatives so this rule doesn't hold". Actually "You can't prove a negative" is actually common short hand for “you can’t prove a universal negative,” or better "existential negative". In other words, you cannot prove that some hypothetical does not exist, anywhere in the universe, because that would require that you be able to look everywhere at the same moment. And, of course, if the hypothetical something, in question is claimed to be invisible and undetectable by any means, in principle, it gets even sillier to attempt to disprove that hypothetical's existence. e.g. God or telepathy etc.Stewgreen2 (talk) 10:11, 7 May 2013 (UTC)

http://en.wikipedia.org/wiki/Talk:Evidence_of_absence

If Stewgreen2 thinks this proves that one can't prove a universal,existential negative then he should consider the following:
The obvious response to this is; you cannot prove that some hypothetical does  not  exist, anywhere in the universe, because that would require that you be able to look everywhere at the same moment. And, of course, if the hypothetical something, in question is claimed to be invisible and undetectable by any means, in principle, it gets even sillier to attempt to dis prove that hypothetical's existence. e.g. God or telepathy etc.


6. A real life proof

The Michaelson/Morley experiment showed how a claim that luminiferous aether, “an invisible and infinite material with no interaction with physical objects”, was proven to not exist. The generalisations that one can't prove a negative, or that one can't prove universal or absolute non-existence [of something], have been disproven. They are false statements. 

I need only one example to disprove the generalisations, just as a single black swan refutes the assumption that all swans are white.