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Meditation 1029
Proving the negative

by: John Tyrrell

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I've probably addressed this in an earlier article on the site, but it bears repeating. The claim "You can't prove a negative" is false.

It is a claim that is regularly put forth by some non-believers in discussions with believers when asked to back up their disbelief by proving there is no god. And they use the canned response "You can't prove a negative."

Unfortunately, the claim has been popularized by the magician, James Randi, who commands a great deal of respect in the skeptic community. And I respect him on most matters too. But still, on this particular issue, he is flat out wrong.

Let me give an example:

Semicolons are not used in this sentence.

You can easily prove that visually. If you don't trust your eyes, you can do it with a CTRL-F.

It is a simplistic example, but it shows that you can prove a negative. Without going to multiple examples, the key in this particular example is the possibility of an exhaustive search. If an exhaustive search is possible then a negative can, at least in theory, be disproved.

In the case of a universal claim such as "You can't prove a negative" all it takes is the one example to disprove it. But let us look at the problem another way.

Nearly* every negative statement can be restated as a positive.

Precisely zero semicolons are used in this sentence.

And of course, nearly* every positive statement can be restated as a negative.**

There is one semicolon in this sentence; it is used to make a point.

can be restated as

This sentence does not contain more than one or less than one semicolon; it's used to make a point.

or if you think both clauses should be made negative

This sentence does not contain more than one or less than one semicolon; it's not used other than to make a point.

Should we think that a little playing around with the grammatical structure of a claim miraculously changes whether it is subject to proof or not?

The point is that there is nothing special about negatives that make them provable or unprovable. Whether something is provable or not depends on what is being proved, not the logical sentence structure of the claim. In the case of God, the very definition (or lack of an agreed coherent definition) makes both the non-existence and the existence of God not provable.

If you wish a deeper but quite readable discussion from a university philosophy department of why negatives are provable, I recommend: THINKING TOOLS: YOU CAN PROVE A NEGATIVE by Steven D. Hales, Bloomsberg University. It's a pdf file which you can download or read in your browser.



* I've used "nearly" because there may be counterexamples - I can't think of one right now.

** In the following discussion, Paul Sharkey provides a simpler and more consistent way to restating negative statement as positives and positives as negatives.


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