Burden of proof
Burden of proof is the position, in argumentation theory, that the individual making a claim that something is true is required to support the claim with evidence or sound argument sufficient to warrant acceptance of the claim by the other party. If the claimant cannot provide sufficient evidence, the other party is allowed to disregard the claim without having to disprove it.
The primary reason why this is important is that the person who is making a claim tends to be the one who has access to the information and evidence. That person is thus the one in the best position to prove it, not the person who's just hearing about it.
While each individual is free to set their own standards of evidence, there are rules and accepted conventions which determine the evidenciary standards in courts of law, formal debates and other settings.
Some familiar examples:
- In the United States legal system, the burden of proof in most criminal trials is on the prosecution (claimant) to prove to a judge or jury that the defendant is guilty (the claim) beyond a reasonable doubt, because there is a presumption of innocence (thus presuming the claim to be false) going into the proceedings.
- Again in the United States, in most civil trials the burden of proof is on the plaintiff (claimant) merely to "tip the scales" in their favor, so that their claim is "more likely true than not" (also known as preponderance of the evidence or balance of probabilities). In this case, there is much more "symmetry" between the two sides of the case, and yet in the unlikely case of a "tie" — complete parity between the two cases presented — judgment must be in favor of the defendent.
Other legal burdens of proof include air of reality, probable cause and clear and convincing evidence. Other non-legal notions of burden of proof include benefit of the doubt and tie goes to the runner.
When asked to support the claim that a god exists, it's not unusual for an apologist to respond with "You can't prove God doesn't exist", or similar statements. Essentially, this is an attempt to shift the burden of proof (a logical fallacy).
A rephrasing of "I believe that god exists" into "I don't believe that god does not exist" is also an attempt to dodge the burden of proof - the proposed equivocation seeks to convert a claim acceptance to a claim rejection, but the two are not logically equivalent. "I don't believe that god does not exist" can be (and often is) a position held by atheists, and says nothing about how the person stands on the claim "god exists".