njhartsh

I think yguy is unfortunately correct that "most atheists," or at least a very large number of us, believe that "proving a negative is impossible."

But every one of them (and yguy too) is mistaken. It is NOT impossible to prove a negative. Here are some fairly easily-proven negative statements:

• There exists no rational number whose square is equal to two.
  
• There exists no highest prime number.
  
• Married bachelors do not exist.

You can be more confident of the above three statements (and many others besides) than you can be that there is in fact a computer monitor in front of you.

Finally, here's a, well, relevant use of the same logical step as the above:

I've seen vast numbers of theists attack one or another of Epicurus' premises above, but I've never seen anyone question what the obvious rational conclusion from logical contradiction has to be.

Richard Carrier, a better philosopher than I, makes this same all-too-important point here.

Let's put the "You can't prove a negative" fallacy to sleep!

- Nathan

Pyrrho

I agree with you. I'll even go further: Most people can prove there are no real live elephants in their room with them, right now as they read this, with as much certainty as they can know that they are sitting in front of a monitor reading this post.

However, what you say will be forgotten by most within a short time, and we can all expect that we will hear "you can't prove a negative" probably before the end of the month.

And, of course, Epicurus is one of the greatest, and most under appreciated, philosophers who ever lived.

http://www.atomic-swerve.net/tpg

http://www.epicurus.net/

Tau

You have a point there, njhartsh. So here's a suggestion for a new and improved version of "Proving a negative is impossible":

It is impossible to prove the universal disexistence of a physical object defined in a way that is not self-contradictory.

This should eliminate the errors you pointed out. The first two are eliminated as they speak of abstract concepts and not physical objects. The third is eliminated as it is a self-contradictory definition. Your error, Pyrrho, is also eliminated, as it is not a universal negative.

I'll admit that I haven't seen "Proving a negative is impossible" used much, but I think the above version should work just as well in at least some of the arguments.

Thomas Metcalf

Originally posted by Tau :

We're almost there. It is impossible to prove the universal nonexistence of a would-be contingent physical object defined in a way that is not self-contradictory. It is possible to prove the nonexistence of some would-be necessary physical objects, like the necessary machine that turns the sky green for one hour every day. We know this exists nowhere (in fact, it's impossible), but it's not self-contradictory.

theophilus

The correct form is, of course, "you cannot prove a universal negative." This statement is unassailable for the reason that no one has universal knowledge.

Your examples are not arguments, they are merely statements which are true by definition, i.e., married bachelors is a contradiction.

There is no logical contradiction in your reference because ignorance does not constitute contradiction. The reference is an example of a false dilema; it defines a problem and limits the solutions in such a way to force the desired conclusion.
God is not bound to work according to our understanding of the way things ought to be. The fact that you may be ignorant of his purposes does not mean that he does not have them and has good reason for doing things the way he does.

theophilus

Ah, but there's the rub; they can have absolutely no confidence that either "proof" is accurate since both are based on sensory experience which is notoriously unreliable.

Thomas Metcalf

Originally posted by theophilus :

Do you think it's possible that married bachelors exist? If your answer is "yes," then my next question is, do you consider yourself to have a competent command of the English language?

Therefore, they don't exist. It makes sense to me.

Tau

Ah, missed that one. Thanks for the correction.

Still, "It is impossible to prove a universal negative," sounds so much nicer. A shame it's incorrect.

njhartsh

And I've conclusively demonstrated that statement to be false, your semantic quibbling notwithstanding.

But innumberable "universal negatives" can be proved without any "knowledge" (save mere axiomatic definitions) at all; and therefore your point is not "unassailable" but immaterial.

I had hoped you would notice that I linked to arguments that conclusively prove the first two of my example universal negatives. What an interesting notion of "proof" you must have, if Pythagoras's impeccable mathematical logic does not qualify.

Proof "by definition" isn't proof? Pray tell, then, how in the world could we ever prove anything? Ever?

A rather irrelevant attack on the substance of the Argument from Evil, which obviously has nothing to do with my point.

Let's take the following argument:

P1. If there were a god, there would be no sdfoiewr in the world.
P2. There is ample sdfoiewr in the world.
----------------------------
C. There is no god.

I have no interest, on this thread, in addressing whether P1 and P2 are correct. I merely quoted Epicurus to show that the above form of argument is clearly valid--and that this is yet another example (presuming that P1 and P2 are true) of a perfectly legitimate proof of a universal negative.

You will be the first person (atheist or theist) I have seen, if you go there, who challenges not only P1 and/or P2 but the validity of deducing C from them. Surely you can't be serious.

- Nathan, by definition

Starseyer

There is a logical fallacy called appeal to ignorance. It relies on the lack of evidence found by an undefined group of people or people who have not conducted a careful systematic (scientific) search for evidence. It goes like this:

All through history people have tried to prove the existance of god(s). No one has definately suceeded. Therefore god(s) do not exist.

Or . . .

Atheists have claimed that there is no God but are unable to prove he doesn't exist. Therefore there is a God.

It wouldn't be a fallacy if there were a qualified group of people (who would they be, anyway?) who performed a systematic search for God (or evidence of god). But since god(s) is a supernatural entity anyway, what would a scientific search prove? God can't be proven or disproven no matter what. As as I see it that makes of the concept of God rather useless.

"Claims that cannot be tested, assertions immune to disproof are veridically worthless, whatever value they they may have in inspiring us or in exciting our sence of wonder." -Carl Sagan, The Demon Haunted World