Can You Prove A Negative?

In my conversations on the existence of God with atheists and skeptics, I've heard this one more than once, "You can't prove a negative" and they therefore think they have nothing to prove, no work to do. Easy peasy, right?. I remember watching a debate on the existence of God, and during the Q&A, some poor undergrad started off by saying, "I just wanna start off by saying that you can't prove a negative. My question for Dr. Craig is..."

What is a negative? In this case,we would say it is the absence of something, or anything with a ~ symbol. So ~God would be unprovable, ~fairies would be unprovable, ~unicorns would be unprovable, etc.

Now, what is atheism? Classically, traditionally, it means that God does not exist. Now if this same atheist says its impossible to prove a negative, then what they're really saying is that its impossible to prove atheism. Yet they're atheists. Yet they can't, by definition, defend themselves. They must therefore remain silent. Then we would never hear a defense for atheism, and it could be easier for people to be Christians. So this slogan, that you can't prove a negative, works against the atheist who torts this out.

This could be advantageous when talking to agnostic. If they say you can't prove a negative, then they have permanently shut the door that could persuade them that Christianity is not true (~Christianity). That's a good thing for us Christians. That means we can always keep trying until they are convinced. They're just waiting to be convinced!

But as it turns out, we can prove a negative. If we can show something to be internally incoherent, we can dismiss the idea. For example, square circles. Do square circles exist? If you cannot prove a negative, then you cannot say no. But the very idea of a square circle is internally incoherent. A circle must, by definition, have no sides. A square, by definition, must have four sides. So the idea of a square circle means that it must have four sides and no sides simultaneously. That is a contradiction. It therefore does not exist. One more example. A two-horned unicorn. Is that possible? A unicorn must, by definition, have one horn (UNI). Therefore, there are no TWO horned UNIcorns. I have proved a negative.

Now, let us take the proposition "I can prove a negative". The negation of that is "I cannot (~) prove a negative". Since the proposition "I cannot prove a negative" is itself a negative statement, it therefore cannot be proven. So why believe it? The proponent of this proposition must therefore remain silent.

Ok, I've been fairly negative (but I can't prove that...see what I did there?) so allow me to give this argument some slack. I think what proponent of this slogan is trying to say is that you have nothing to prove in negative epistemic claim to knowledge. In epistemology (or the study/theory of knowledge), there are positive and negative claims to knowledge. A positive claim to knowledge is "God exists", "My keys are locked in my car" "The girl I love wont love me back", or "my baby is going to be a boy". They are all claiming to know something, and therefore have a burden of proof. The negative claims to knowledge of these same propositions are "I don't know if God exists", "I don't know if my keys are in the car", "I don't know if the girl I love loves me back", and "I don't know if my baby is going to be a boy". In these second set of claims, they aren't claiming to know anything, and therefore have nothing to prove.

But statements like "God does not exist" is not a negative claim to knowledge. They are indeed saying, God does NOT exists, and this I KNOW. Same thing with keys. My keys are not in my car, and I know this because I have them in my hand. The girl I love does not love me back, and I know this because she told me so. The baby will not be a boy, and I know this because the sonogram showed its going to be a girl.

So don't be so negative.