“You can’t prove a negative.”
People who are searching for excuses to believe silly things frequently make this statement. A theist makes a positive assertion, and then declines to provide a basis for it. You deny their assertion (rightly so, what with no basis and all), but your denial is deemed invalid because it is impossible to prove a denial.
There is so very much wrong with this situation, it will take a while to wade through it.
The rules of logic and science indicate that there must be some kind of basis (either in substance or in thought) for an assertion or else it must be denied. An assertion, without evidence, is not accepted as true. That is the default position, the position that defines what critical thought is. Critical thought means not believing things you are told unless there is evidence to back it up. And without critical thought, logic and science are abandoned, and this is the only kind of productive thought humanity has ever come up with. To reject critical thought is to turn one’s back on thinking and embrace the Dark Ages. That’s the answer to this statement in theory.
However, in practice, there is usually a lot more happening with the person who makes such a proclamation. The person who makes this kind of statement has a great many fundamental misunderstandings about the nature of logic, science, and productive thought.
First, many people who believe in God do not realize that in every discussion about theism, their assertion is implicit: God exists. They do not need to say it. Every argument they make is under the assumption that the statement “God exists” is true. The fact that they identify themselves as believers is enough to serve as an assertion that a deity or deities exists. No assertion is being made by an atheist (at least not a smart atheist). The word “god” hasn’t even been defined and the nature of belief in that god has not been described; these must take place before any substantial discussion about the nature of God can begin. Atheists have no reason to provide these descriptions – without any beliefs about God, they have no reason to do so. It must be presumed that this onus rests upon the theist. The mere mention of one’s belief in God serves as an assertion that God exists.
Secondly, a person who rejects an assertion does not need to provide any justification for it. The evidence has to be provided by the party making the assertion. The person rejecting the assertion needs to provide nothing at all. Many theists try to escape this basic fact of life by declaring (in opposition to common sense) that their assertions need to be justified only to themselves in their personal experience. Simply put, that what is true for others might not be true for themselves. But this is madness – this also turns its back on productive thinking. This idea is called “solipsism,” and it refers to the notion that every person lives in his own reality, and what is true in his or her life might not be true for others. This is an old idea and it was shown to be ridiculous many centuries ago. Think about it – if it solipsism really was real, there wouldn’t be any books, schools, learning, or science. And people would never be able to communicate effectively.
Thirdly, the statement that “you cannot prove a negative” is simply false. On the surface, it seems to be true: if Person A says “I think God exists” and Person B says “I don’t think God exists,” it’s pretty clear that Person B is going to have a hard time proving that there isn’t a God. However, if you look a little closer, it actually depends on the nature of the negative statement being made. Here are some negative statements that can be proven very easily:
The ancient Egyptians did not watch Seinfeld
The tsetse fly is not native to North America
Clearly, it’s possible to prove a negative statement. The real problem here is clearly the nature of the positive statement being refuted. When a person asserts that God exists, he does not specify the nature of God – that is, is God small, large, blue, red? And where is he? Of course it is not possible to prove that God does not exist, if “God” is a thing that has no definition, no characteristics, and no location. In fact, you can prove just about any kind of negative you can think of – except for (surprise!) the non-existence of mystical beings. When you get right down to it, the statement “you cannot prove a negative” is really just a different way of saying “You can’t prove me wrong because I don’t even know what I’m talking about.”
Logical statements have to abide by certain rules and restrictions. In order for a statement to be logical, it must be falsifiable, which means that it has to be presented in such a way that it could be proven incorrect. A statement is not logical if it cannot be tested to make sure it is true. The existence of God is not a logical question at all, and is therefore nonsensical. Of course you can’t prove that God doesn’t exist – no one even knows what God is supposed to be.