In the study of epistemology, one will easily run across the Latin phrase "onus probandi," that is translated as burden of proof.

An understanding of the burden of proof is a necessity before beginning any argument, debate, or defense of a particular topic. Without knowing where to draw the line for defense, and the prosecution will end up frustrated and lost in a completely useless discussion. Take the example below, posed by none other than Betrand Russell:

Nobody can prove that there is not between the Earth and Mars a china teapot revolving in an elliptical orbit, but nobody thinks this sufficiently likely to be taken account in daily practice.

Russell employed the use of a reductio ad absurdium to show just how impossible it was to disprove god, and likewise demonstrate how little impact that was to his daily life. Russell was not saying that there could not be a god, just that the likelihood that there was, was not meaningful enough to merit any change to daily activity.

The analogies abound in similarity to Russell's Teapot (as it has been coined). An entire branch of "religion" has been invented called "Pastafarianism," which teaches that the Flying Spaghetti Monster created the universe--a stab at the belief in a god.

Which brings us back to the Latin phrase I mentioned earlier, the burden of proof. What is the burden of proof?

In a courtroom, the burden of proof is the concept extended by the phrase "innocent, until proven guilty," a man on trial will incur no punishment until he is proven guilty. The defense does not even need to make a peep to defend, if the prosecution is unable to levy a convincing argument.

Philosophically and logically, the phrase is of a slightly different slant, but nonetheless just as impactful. A claim is only as good as the evidence to back it. A claim with no backing evidence can be dismissed without counter argument. This prevents wild fabrications from holding the same factual status as actual facts. This is why any normal person scoffs at the idea that the Earth is flat, or we are all secretly being lied to by the government, and the president is actually an alien from another planet. This is why conspiracy theories are just that: wild imaginations with no real evidence.

But why do they need evidence? Isn't it the job of each individual to weigh the pros and cons of such a claim and determine if it is true? Yes and no. Logically, it is perfectly acceptable to be a skeptic and respond by rejecting a claim before it is proven true.

For example, suppose I told you that I had a cat that could change colors--like a chameleon. He is a brown tabby and can change his fur to that of purple and green, almost like a fiber optic.

If supposing you thought me a reasonable person (not insane or prone to schizophrenia or something), you might humor me and believe my claim. However, you would be prudent and so would our mutual friend (we'll call him Bob) if you refused to believe it until I showed you.

Such is the stance of a skeptic. Logically, it is right and often best to accept a claim on reasonable evidence, and refuse to believe claims that are:

1. Extraordinary and unbelievable
2. Unfounded
3. Patterned after hoaxes
4. Unfalsifiable
5. Without meaning or substance to them
6. Already having been disproved by another known fact (direct contradiction)

Examples of each might include:

1. The moon is made out of cheese and NASA has covered it up!
2. Gravity is really just a giant contraption inside the Earth that creates an electromagnetic pull.
3. A Nigerian prince just called me and gave me a million dollars.
4. Elephants run through my house all the time; they are just too fast for anyone to see or hear them.
5. Rectangles are evil.
6. The Earth is the center of the universe.

So, when a claim is made, the party making it has to convince the hearer of the claim. Each hearer may have a different level of acceptance of the claim, but the party making claim should still be the one to convince them.

In my instance above, in order to prove to you that my cat could change colors, I might show you a picture and you would be convinced, but Bob might still not be. If I showed him the cat in person, he might still not believe, but think it was some kind of prank we were pulling on him. Bob would be warranted in his position.

Here is what we (as thinking, rational people) want to avoid... ...we don't want to:

• believe just because someone told us to
• believe without evidence
• believe it because we like the belief
• assume it is true until otherwise proven false
  • (This is the logical fallacy of "argument from ignorance." It's essentially saying because I can't prove it false, then it must be true--because I can't prove that aliens made our entire universe five minutes ago, then they must have done it.)

Hopefully that clears up some about the burden of proof, and why it is on theists' shoulders to prove a god's existence: they have made the claim that a god exists. It is reasonable to assume that there is no god (not that there cannot be a god) until proven otherwise. Like Russell was saying, if it can't be proven to be true, then it has little impact on his daily life.